Sensitivity Analysis of Soil Site Response Modelling in Seismic ... - ITC
Sensitivity Analysis of Soil Site Response Modelling in Seismic ... - ITC
Sensitivity Analysis of Soil Site Response Modelling in Seismic ... - ITC
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<strong>Sensitivity</strong> <strong>Analysis</strong> <strong>of</strong><br />
<strong>Soil</strong> <strong>Site</strong> <strong>Response</strong><br />
<strong>Modell<strong>in</strong>g</strong> <strong>in</strong> <strong>Seismic</strong><br />
Microzonation for<br />
Lalitpur, Nepal<br />
Umut DESTEGÜL<br />
March 2004
<strong>Sensitivity</strong> <strong>Analysis</strong> <strong>of</strong> <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong><br />
<strong>Modell<strong>in</strong>g</strong> <strong>in</strong> <strong>Seismic</strong><br />
Microzonation for<br />
Lalitpur, Nepal<br />
By<br />
Umut DESTEGÜL<br />
Thesis submitted to the International Institute for Geo-<strong>in</strong>formation Science and Earth Observation <strong>in</strong><br />
partial fulfilment <strong>of</strong> the requirements for the degree <strong>of</strong> Master <strong>of</strong> Science <strong>in</strong> Earth Resources and Environmental<br />
Geosciences.<br />
NATURAL HAZARD STUDIES<br />
Degree Assessment Board<br />
Pr<strong>of</strong> . Dr. F. D. (Freek ) van der Meer<br />
Pr<strong>of</strong>. Dr. S. B. (Salomon Bernard) Kroonenberg<br />
Dr. C. J. (Cees) van Westen<br />
Ir. S. (Siefko) Slob<br />
Dr. P. M. (Paul) van Dijk<br />
Chairman<br />
External Exam<strong>in</strong>er, Delft University<br />
First Supervisor<br />
Second Supervisor<br />
Internal Exam<strong>in</strong>er<br />
INTERNATIONAL INSTITUTE FOR GEO-INFORMATION SCIENCE AND EARTH OBSERVATION<br />
ENSCHEDE, THE NETHERLANDS<br />
II<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
Disclaimer<br />
This document describes work undertaken as part <strong>of</strong> a programme <strong>of</strong> study at the International<br />
Institute for Geo-<strong>in</strong>formation Science and Earth Observation. All views and op<strong>in</strong>ions expressed<br />
there<strong>in</strong> rema<strong>in</strong> the sole responsibility <strong>of</strong> the author, and do not necessarily represent those <strong>of</strong> the<br />
<strong>in</strong>stitute.<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal<br />
III
Acknowledgement<br />
First <strong>of</strong> all, I would like to express my gratitude to Netherlands organization for <strong>in</strong>ternational cooperation<br />
<strong>in</strong> higher education (Nuffic) that I had the opportunity to study <strong>in</strong> <strong>ITC</strong>, and experience a lot more,<br />
dur<strong>in</strong>g this 18 months period. It is pity that Turkey is no longer <strong>in</strong> the list, thus I believe many other<br />
colleagues could have benefited from this unique opportunity.<br />
Secondly, I would like to express my gratitude to my first supervisor; Mr. Westen for his guidance and<br />
support <strong>in</strong> all phases <strong>of</strong> my thesis. His cont<strong>in</strong>uous detailed reviews and suggestions on my challeng<strong>in</strong>g<br />
works, made it possible to come to an end. And, I would like to thank my second supervisor Mr. Slob.<br />
From the early beg<strong>in</strong>n<strong>in</strong>g <strong>of</strong> the thesis, he has been very k<strong>in</strong>d to spare time and contribute to very fruitful<br />
discussions on the research topic.<br />
I would like to thank to Mr. De Mann, for keep<strong>in</strong>g an eye on me and my work dur<strong>in</strong>g the fieldwork<br />
and afterwards. His guidance is very appreciated. And also, my respectful gratitude goes to Mr. Brussels,<br />
Mr. Ellis, Mr. Boerboom for not leav<strong>in</strong>g me alone with the important meet<strong>in</strong>gs <strong>in</strong> Nepal. And to<br />
my fieldwork companions, first to jump<strong>in</strong>g team; Jimmy and Tung, and second to Senani, Tung, Mazharul,<br />
and Jeewan. And my respectful thanks also goes to Mr. Ranamagar, who has opened his library<br />
and files without hesitation <strong>in</strong> Kathmandu. And to NSET and ICIMOD staff who have been very k<strong>in</strong>d<br />
to host us <strong>in</strong> many situations, especially to Mr. Dhakal who has assisted me <strong>in</strong> the field.<br />
I am very grateful to my student advisor, Mr. Voskuil for be<strong>in</strong>g there when I needed, with a great support<br />
<strong>in</strong> any subject. The endless care and support <strong>of</strong> Mrs. K<strong>in</strong>gma, led me easily through many obstacles.<br />
And, with Mr. Damen they all made me feel that I am not that far from home.<br />
Also, I would like to express my gratitude to Mr. Van Dijk, for his contributions and support on many<br />
topics from the very beg<strong>in</strong>n<strong>in</strong>g <strong>of</strong> my study <strong>in</strong> <strong>ITC</strong>.<br />
Thanks to Mr. Rossiter for his reassurances on my work and for his special conversations. And to Mr.<br />
Sporry, Mr. Alkema, Mr. Ordonez, Mr. Avouac, Mr. Ste<strong>in</strong>, Mr. Woldai for their valuable discussions<br />
and contributions.<br />
I am very grateful to my cluster friends, Maria, Marl<strong>in</strong>a, Maulida, Syarif, Pablo, Piya that they have<br />
been great supporters <strong>in</strong> many cases. And, I would like to thank to Amani for be<strong>in</strong>g my family when I<br />
am away from them. Particularly, I would like to thank to Ana for be<strong>in</strong>g my company <strong>in</strong> hardship and<br />
fun. And, to my compatriot, Derya.<br />
And most importantly, I would like to express my deepest gratitude to my parents, for their endless<br />
support and love.<br />
Lastly, to my spirit companion; Ozdem, for be<strong>in</strong>g so patient and encourag<strong>in</strong>g partner for all these time.<br />
II<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
Abstract<br />
For a proper design <strong>of</strong> earthquake-resistant structures and facilities a good estimation <strong>of</strong> the ground<br />
amplification level dur<strong>in</strong>g the expected earthquake is required. The level <strong>of</strong> shak<strong>in</strong>g is mostly described<br />
<strong>in</strong> terms <strong>of</strong> peak ground acceleration and amplification, and visualised by response spectra. In<br />
order to determ<strong>in</strong>e the ground response us<strong>in</strong>g a one-dimensional numerical approach, several <strong>in</strong>put<br />
parameters are required for each site. These <strong>in</strong>clude: soil pr<strong>of</strong>ile and bedrock level; shear strength<br />
and other geotechnical properties <strong>of</strong> the subsurface and the “design earthquake”. In most cases, many<br />
<strong>of</strong> these <strong>in</strong>put parameters are very poorly known. This study describes, through a sensitivity analysis,<br />
which <strong>of</strong> these <strong>in</strong>put parameters are the most important to know and with which accuracy <strong>in</strong> order to<br />
arrive at a proper estimation <strong>of</strong> the expected amplifications. This study <strong>in</strong>cluded also the development<br />
<strong>of</strong> a method to create a seismic microzonation map on the basis <strong>of</strong> a simplified geological subsurface<br />
GIS model. The results <strong>of</strong> this microzonation study were compared with actual borehole data and the<br />
reliability <strong>of</strong> this simplified model was determ<strong>in</strong>ed.<br />
Key words: <strong>Soil</strong> site effects, sensitivity analysis, seismic microzonation, shear wave velocity, Kathmandu<br />
Valley<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal<br />
III
Table <strong>of</strong> Contents<br />
Page<br />
Acknowledgement............................................................................................................................... ii<br />
Abstract .............................................................................................................................................. iii<br />
Table <strong>of</strong> Contents ...............................................................................................................iv<br />
List <strong>of</strong> Figures .................................................................................................................... vi<br />
List <strong>of</strong> Tables...................................................................................................................... ix<br />
List <strong>of</strong> Abbreviations............................................................................................................x<br />
1. Introduction ....................................................................................................................................1<br />
1.1. Scope <strong>of</strong> the study ....................................................................................................................1<br />
1.2. Problem Statement ...................................................................................................................4<br />
1.3. Research Objectives .................................................................................................................5<br />
1.4. Research Methodology.............................................................................................................5<br />
1.4.1. Input data..........................................................................................................................6<br />
1.4.2. Data collection................................................................................................................11<br />
1.4.3. Data organization ...........................................................................................................13<br />
1.4.4. Structure <strong>of</strong> the Thesis....................................................................................................14<br />
2. Literature Review.........................................................................................................................16<br />
2.1. Overview Of Methods For <strong>Seismic</strong> Hazard Assessment........................................................17<br />
2.1.1. <strong>Seismic</strong> Hazard Assessment ...........................................................................................17<br />
2.1.2. <strong>Seismic</strong> Microzon<strong>in</strong>g......................................................................................................22<br />
2.1.3. Ground <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong>; <strong>Soil</strong> <strong>Site</strong> Effects..............................................................24<br />
Experimental Methods ...................................................................................................................24<br />
Numerical <strong>Analysis</strong> ........................................................................................................................30<br />
Advanced methods .........................................................................................................................32<br />
Empirical and semi-empirical methods ..........................................................................................33<br />
2.1.4. <strong>Sensitivity</strong> <strong>Analysis</strong>........................................................................................................34<br />
2.2. Conclusıons ............................................................................................................................36<br />
3. Shake2000 .....................................................................................................................................38<br />
3.1. Introduction ............................................................................................................................38<br />
3.2. Background ............................................................................................................................38<br />
3.3. Program Structure...................................................................................................................41<br />
4. Study Area ....................................................................................................................................49<br />
4.1. Location..................................................................................................................................49<br />
4.2. Geology ..................................................................................................................................50<br />
4.3. <strong>Seismic</strong>ity ...............................................................................................................................54<br />
5. <strong>Seismic</strong> <strong>Response</strong> <strong>Analysis</strong> For Lalitpur, Nepal ........................................................................56<br />
5.1. Ground <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> Methodology ...........................................................................56<br />
5.1.1 Methodology 1: <strong>Modell<strong>in</strong>g</strong> based on available borehole data........................................57<br />
5.1.2 Methodology 2: Generat<strong>in</strong>g acceleration maps..............................................................74<br />
6. <strong>Sensitivity</strong> <strong>Analysis</strong>.......................................................................................................................85<br />
6.1. Methodology ..........................................................................................................................85<br />
6.2. <strong>Sensitivity</strong> to changes <strong>in</strong> Shear Wave Velocity......................................................................86<br />
6.3. <strong>Sensitivity</strong> to Input Motions...................................................................................................90<br />
IV<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
6.4. <strong>Sensitivity</strong> for Unit Weight ....................................................................................................93<br />
6.5. <strong>Sensitivity</strong> for soil thickness...................................................................................................95<br />
6.6. Conclusions on the <strong>Sensitivity</strong> <strong>Analysis</strong> ................................................................................97<br />
7. Discussion, conclusions and recommendations..........................................................................99<br />
7.1. Discussions and Recommendations .......................................................................................99<br />
7.2. General Conclusions.............................................................................................................103<br />
References ........................................................................................................................105<br />
Appendix A: Input Strong Ground Motion (3 Scenario)..................................................109<br />
Appendix B: <strong>Soil</strong> Pr<strong>of</strong>ile Information On Calculations Done In Shake2000...................112<br />
Appendix C: Generalized <strong>Soil</strong> Pr<strong>of</strong>ile Frequency Values................................................119<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal<br />
V
List <strong>of</strong> Figures<br />
Figure 1-1 The risk management cycle show<strong>in</strong>g the sequence <strong>of</strong> assessment, response and education<br />
which is essential for successful disaster reduction (Smith 2001). ..................................................1<br />
Figure 1-2 The seismic hazard map <strong>of</strong> Asia depict<strong>in</strong>g peak ground acceleration (PGA), given <strong>in</strong> units<br />
<strong>of</strong> m/s2, with a 10% chance <strong>of</strong> exceedance <strong>in</strong> 50 years. The site classification is Rock. (Zhang,<br />
Yang et al. 1992-1999).....................................................................................................................3<br />
Figure 1-3 Flowchart <strong>of</strong> the methodology used <strong>in</strong> the research. ..............................................................7<br />
Figure 1-4 A representation <strong>of</strong> the crosshole tomography method. Left borehole consists <strong>of</strong> the<br />
transmission signals and the right one has the geophones, which receives the signals transmitted<br />
from the other borehole. .................................................................................................................10<br />
Figure 1-5 The borehole names and locations that are used <strong>in</strong> the analysis...........................................14<br />
Figure 1-6 Figure show<strong>in</strong>g the contacts, data collected and metadata relation diagram........................15<br />
Figure 2-1The four steps <strong>of</strong> probabilistic seismic hazard analysis (Kramer 1996)................................18<br />
Figure 2-2 A probabilistic seismic hazard map show<strong>in</strong>g U.S. for the peak acceleration (%g) with %10<br />
probability <strong>of</strong> exceedance <strong>in</strong> 50 years (USGS 2003). ....................................................................19<br />
Figure 2-3 The illustration <strong>of</strong> the s<strong>in</strong>gle degree <strong>of</strong> freedom systems. ....................................................20<br />
Figure 2-4 The determ<strong>in</strong>istic seismic hazard assessment diagram <strong>in</strong> steps (Kramer 1996). ..................21<br />
Figure 2-5 Diagram show<strong>in</strong>g the topographic and soil site effects. <strong>Seismic</strong> waves travel through the<br />
settlements pass<strong>in</strong>g the Rock site and soil site. For both the soil site and the Rock hill top there is<br />
generally a referr<strong>in</strong>g topographic effect such as hill top, ridge and bas<strong>in</strong> effects. .........................22<br />
Figure 2-6 Two simple topographic irregularities. (a) a triangular wedge (b) approximation <strong>of</strong> real<br />
surface at rough and crest by wedges (Faccioli, 1991) ..................................................................23<br />
Figure 2-7 The microtremors are placed to an alluvial site, a Rock site and at the top <strong>of</strong> a hill. The<br />
record<strong>in</strong>gs are received and processed. Then, the amplification spectrum is plotted. The<br />
differences between the sites are expla<strong>in</strong>ed us<strong>in</strong>g the ratios and comparisons <strong>of</strong> the H/V<br />
components. This method refers to Standard Spectral Ratio <strong>of</strong> site effect estimations (Duval,<br />
1994) ..............................................................................................................................................26<br />
Figure 2-8 Figure show<strong>in</strong>g the representative situation for Poisson’s ratio on material. (Lakes 2004).27<br />
Figure 2-9 Transfer functions for (a) Standard spectral ratio (e) H/V ratio for S wave part <strong>of</strong> the<br />
earthquake records (f) Nakamura’s technique (H/V ratio <strong>of</strong> ambient vibrations). Dashed l<strong>in</strong>e<br />
represent 95% confidence limits <strong>of</strong> the mean ((Lacave, Bard et al. 2002).....................................28<br />
Figure 2-10 The <strong>in</strong>cident wave and its reflected and refracted components <strong>in</strong> two media. (Transverse<br />
waves are S-waves and longitud<strong>in</strong>al waves are the P-waves). .......................................................29<br />
Figure 2-11 Subsurface geology could be referred as one-dimensional, two-dimensional or threedimensional<br />
(Smith 2001). .............................................................................................................32<br />
Figure 2-12 Diagram show<strong>in</strong>g the cont<strong>in</strong>uum and the nodal po<strong>in</strong>ts (Kramer, 1996).............................33<br />
Figure 2-13 The diagram for the Empirical Green’s function method (Bour 1994) ..............................34<br />
Figure 3-1 An <strong>in</strong>tensity map done by rapid <strong>in</strong>strumental technique. (Wald, 1999)...............................39<br />
Figure 3-2: Diagram show<strong>in</strong>g the relationships between Shake s<strong>of</strong>tware..............................................40<br />
Figure 3-3 The ma<strong>in</strong> menu <strong>of</strong> Shake2000 s<strong>of</strong>tware. ..............................................................................42<br />
Figure 3-4 The w<strong>in</strong>dow for choos<strong>in</strong>g and fill<strong>in</strong>g <strong>in</strong> the options for Shake2000. ...................................43<br />
Figure 3-5 The first option from the earthquake response analysis for the dynamic material properties.<br />
........................................................................................................................................................44<br />
Figure 3-6 The w<strong>in</strong>dow where the soil pr<strong>of</strong>ile is implemented..............................................................44<br />
VI<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
Figure 3-7 The display <strong>of</strong> results for the analysis <strong>in</strong> table format..........................................................46<br />
Figure 4-1 Small map show<strong>in</strong>g Asia, the rectangle <strong>in</strong>dicates Nepal. Also, Lalitpur is <strong>in</strong>dicated <strong>in</strong> Nepal<br />
map.................................................................................................................................................49<br />
Figure 4-2 Study area; Lalitpur. North <strong>of</strong> Lalitpur is Kathmandu City..................................................50<br />
Figure 4-3 From south to north it can be seen, ma<strong>in</strong> frontal fault system, ma<strong>in</strong> boundary trust and the<br />
ma<strong>in</strong> central trust boundaries. The Indus Suture Zone starts from the border <strong>of</strong> north side<br />
(Avouac, Boll<strong>in</strong>ger et al. 2001)......................................................................................................51<br />
Figure 4-4 Geology map <strong>of</strong> the Kathmandu Valley and the Lalitpur city..............................................53<br />
Figure 4-5 Taken from Bilham et al (2001) this figure shows the seismic gap regions and the potential<br />
magnitudes for the Himalayan region. It can be seen that Kathmandu has a potential slip <strong>of</strong> 4 m<br />
for certa<strong>in</strong> and even more is possible. ............................................................................................54<br />
Figure 4-6 Map show<strong>in</strong>g, seismic data for the years between 04/01/1995 and 10/12/1999, geodetic<br />
measurements and major geological structures with (MFT, MBT, MCT) (Catt<strong>in</strong> and Avouac<br />
2000). .............................................................................................................................................56<br />
Figure 5-2 Flowchart <strong>of</strong> the method 1....................................................................................................61<br />
Figure 5-3 The deep boreholes correspondent PGA values for the shear wave velocity set 1 (A:<br />
m<strong>in</strong>imum Vs values) and 2 (B: maximum Vs values)....................................................................66<br />
Figure 5-4 The response spectrum curves for three critical boreholes and correspondent po<strong>in</strong>ts for the<br />
earthquake scenarios (For PR 16 LA M=6.2). ...............................................................................69<br />
Figure 5-5 The response spectrum curves for three critical boreholes and correspondent po<strong>in</strong>ts for the<br />
earthquake scenarios (M=8, R=48km for B23).............................................................................70<br />
Figure 5-6 The response spectrum curves for three critical boreholes and correspondent po<strong>in</strong>ts for the<br />
earthquake scenarios (M=8, R=48km for B25)..............................................................................71<br />
Figure 5-7 The stratigraphic section <strong>of</strong> P37 borehole log. .....................................................................72<br />
Figure 5-8 The Figure is show<strong>in</strong>g the actual borehole (ID: P37) and the po<strong>in</strong>t read from the<br />
generalized soil pr<strong>of</strong>ile. A and C belongs to the actual borehole. The A and B are the response<br />
spectra for the chosen scenario earthquake (Los Angeles M: 6.2; D: 15 km)................................73<br />
Figure 5-9 The Figure is show<strong>in</strong>g the actual borehole (ID: P37) and the po<strong>in</strong>t read from the<br />
generalized soil pr<strong>of</strong>ile. A and C belongs to the actual borehole, the others C and D are from the<br />
generalized pr<strong>of</strong>ile. The C and D are the amplification spectrums for chosen scenario earthquake<br />
(Los Angeles M: 6.2; D: 15 km). ...................................................................................................74<br />
Figure 5-10 Flowchart <strong>of</strong> the method 2..................................................................................................75<br />
Figure 5-11 The dynamic material properties and their relation to the shear stra<strong>in</strong>, which are used for<br />
the four-layer soil pr<strong>of</strong>ile. (a and b) ...............................................................................................77<br />
Figure 5-12 The illustration <strong>of</strong> the generalized subsurface geology <strong>of</strong> the Kathmandu Valley.............78<br />
Figure 5-13 The <strong>in</strong>tensity maps visualized from JICA report. (JICA, 2001) The <strong>in</strong>tensities are for the<br />
scenario earthquakes named (from left through right) respectively; Mid Nepal, Kathmandu Valley<br />
Local and North Bagmati. ..............................................................................................................79<br />
Figure 5-14 The second methodology’s <strong>in</strong>puts and outputs. The first part represents the calculations<br />
with Shake 2000. The second part was done <strong>in</strong> ILWIS us<strong>in</strong>g 60 po<strong>in</strong>ts derived from the 500 m<br />
pixel sized thickness map. ..............................................................................................................82<br />
Figure 5-15 Graph show<strong>in</strong>g the resonance maps correspond<strong>in</strong>g to frequencies; 1, 2, 3 and 5 Hz and the<br />
MMI map for the worst scenario earthquake and soil thickness map. ...........................................83<br />
Figure 5-16 The natural frequency maps for 500, 800 and 1500 m/s shear wave velocities. ................84<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal<br />
VII
Figure 6-1 Methodology <strong>of</strong> the sensitivity analysis. In the analysis shear wave velocity unit weight and<br />
thickness had been also variables. The program was run for the selected range <strong>of</strong> values for the<br />
variables and the output PGA values are plotted aga<strong>in</strong>st the variable values. ...............................86<br />
Figure 6-2 Calculated PGA values for different shear wave velocities. The blue dotted curve is the<br />
orig<strong>in</strong>al curve obta<strong>in</strong>ed by plott<strong>in</strong>g the two data sets aga<strong>in</strong>st each other. The p<strong>in</strong>k l<strong>in</strong>e is the trend<br />
l<strong>in</strong>e obta<strong>in</strong>ed from this orig<strong>in</strong>al curve. ...........................................................................................87<br />
Figure 6-3 The PGA values obta<strong>in</strong>ed after the runn<strong>in</strong>g <strong>of</strong> Shake2000 for the shear wave velocity<br />
sample set. ......................................................................................................................................88<br />
Figure 6-4 Graph show<strong>in</strong>g the <strong>in</strong>itial analysis for PGA values obta<strong>in</strong>ed for different shear wave<br />
velocities <strong>in</strong> two-layer model. Series 1 is Sand and series 2 is Clay. The x-axis shows Vs values;<br />
y-axis shows the PGA (g) values. ..................................................................................................89<br />
Figure 6-5: Graph show<strong>in</strong>g the PGA values that are obta<strong>in</strong>ed for the 3 different earthquakes (Scenario<br />
1, 2, and 3) from the methodology 1 / Model 2. The black arrow shows the range <strong>of</strong> PGA’s that<br />
could be <strong>in</strong> the site. Amax is the maximum acceleration recorded <strong>in</strong> time doma<strong>in</strong> <strong>of</strong> the<br />
earthquake. .....................................................................................................................................91<br />
Figure 6-6: A and C graphs show the response spectra <strong>of</strong> two boreholes (B25 and B23) for the first<br />
scenario earthquake (M=8; R=48km). B and D show the response spectra for the same boreholes<br />
but with the third scenario earthquake (M=6.7; D=6.4 km). Please note that the y-axis range is<br />
differ<strong>in</strong>g <strong>in</strong> each graph. ..................................................................................................................93<br />
Figure 6-7: The correlation between PGA values and the unit weights (Two layer model)..................94<br />
Figure 6-8: Unit weight and PGA relations for a two-layer soil pr<strong>of</strong>ile (Sand and Clay)......................95<br />
Figure 6-9 The relation between PGA values and depth difference <strong>in</strong> a two-layer model. Sand was<br />
used for the two-layer model. The Rock layer shear wave velocity was 9842 f/s. ........................96<br />
Figure 6-10 Two-layer model for the analysis <strong>of</strong> thickness and PGA values sensitivity results. ..........97<br />
Figure 7-1 The response spectrum show<strong>in</strong>g the l<strong>in</strong>ear and non-l<strong>in</strong>ear approach results; SHAKE is<br />
l<strong>in</strong>ear and MARES is the non-l<strong>in</strong>ear. Compare the maximum and the difference between the two.<br />
......................................................................................................................................................103<br />
VIII<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
List <strong>of</strong> Tables<br />
Table 1-1 Investigation list <strong>in</strong> groups <strong>of</strong> different methods, from surface and by drill<strong>in</strong>g. .....................8<br />
Table 1-2 The names and abbreviations <strong>of</strong> the organizations contacted <strong>in</strong> the fieldwork. ....................12<br />
Table 1-3 The borehole names and locations that are used <strong>in</strong> the analysis (Wald, 1999)......................13<br />
Table 3-1 The conversion formulas used <strong>in</strong> the calculations for Shake2000.........................................42<br />
Table 4-1 Important high magnitude earthquakes happened <strong>in</strong> the Himalayan region..........................55<br />
Table 5-1 Actual Deep and shallow boreholes.......................................................................................58<br />
Table 5-2 The borehole po<strong>in</strong>ts and their correspond<strong>in</strong>g thickness’ read from the generalized pr<strong>of</strong>ilee.<br />
........................................................................................................................................................58<br />
Table 5-3 Assumed shear wave velocity values for different soil types. ...............................................59<br />
Table 5-4 Strong ground motion obta<strong>in</strong>ed from the PEER Strong Motion database (Silva 2000). .......63<br />
Table 5-5 The selected 3 scenario earthquakes form the Shake2000 strong motion database...............64<br />
Table 5-6 Generalized soil pr<strong>of</strong>ile values that are used <strong>in</strong> the soil site analysis. ...................................65<br />
Table 5-7 The chosen po<strong>in</strong>ts (they correspond to actual boreholes) from the generalized 4 layer pr<strong>of</strong>ile.<br />
........................................................................................................................................................68<br />
Table 5-8 Four-layer generalized soil pr<strong>of</strong>iles attributes that are used <strong>in</strong> the response calculation <strong>in</strong><br />
Shake2000. .....................................................................................................................................75<br />
Table 5-9 Dynamic material properties are shown for the four-layer generalized model......................76<br />
Table 5-10 The relations between the fundamental frequencies and the storey numbers <strong>of</strong> the build<strong>in</strong>gs<br />
from three different sources (Vidal and Yamanaka 1998; INGEOMINAS 1999; Day 2001). ......80<br />
Table 5-11 The fundamental frequencies for Lalitpur and their storey numbers...................................80<br />
Table 6-1 The comparison table for the PGA ranges <strong>of</strong> the consequent scenario earthquakes..............91<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal<br />
IX
List <strong>of</strong> Abbreviations<br />
PGA<br />
SA<br />
SDOF<br />
Vs<br />
UW<br />
RS<br />
H/V<br />
SPT<br />
JICA<br />
: Peak Ground Acceleration<br />
: Spectral Acceleration<br />
: S<strong>in</strong>gle Degree <strong>of</strong> Freedom System<br />
: Shear Wave Velocity<br />
: Unit Weight<br />
: <strong>Response</strong> Spectrum<br />
: Horizontal and Vertical component ratio <strong>of</strong> seismograms<br />
: Standard Penetration Test<br />
: Japan International Cooperation Agency<br />
X<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
1. Introduction<br />
1.1. Scope <strong>of</strong> the study<br />
Natural disasters such as earthquakes, floods, tornados and drought are unavoidable, but we can mitigate<br />
their effects by disaster prevention systems. Earthquakes are the most destructive <strong>of</strong> the various<br />
geological hazards. Dur<strong>in</strong>g the twentieth century, well over 1,000 fatal earthquakes were recorded<br />
with a cumulative loss <strong>of</strong> life estimated at 1.5-2.0 million people (Pomonis 1993). In order to reduce<br />
the casualty numbers, we have to know more about the hazard status and f<strong>in</strong>d out how to decrease the<br />
effects. On the whole, this can be done us<strong>in</strong>g risk management. Risk management has three ma<strong>in</strong><br />
phases; pre-disaster, dur<strong>in</strong>g disaster and post-disaster. The pre-disaster phase <strong>in</strong>volves the hazard, vulnerability<br />
and risk assessments. Here the hazard and the effects on the community are def<strong>in</strong>ed. Dur<strong>in</strong>g<br />
disaster emergency actions are taken. In case <strong>of</strong> earthquakes, which have a very short time to take action,<br />
clos<strong>in</strong>g down the electricity, gases etc. are examples <strong>of</strong> dur<strong>in</strong>g disaster actions. Post-disaster deals<br />
with relief, rehabilitation, reconstruction <strong>of</strong> build<strong>in</strong>gs and implementation <strong>of</strong> the knowledge to the<br />
regulations. Hazard assessment, can also be analysed <strong>in</strong> another cycle where it focuses on risk management<br />
with relation to education <strong>of</strong> the community and world (Smith 2001). Look<strong>in</strong>g at the diagram<br />
(Figure 1-1), it can be seen that this research takes <strong>in</strong> the prelim<strong>in</strong>ary phases <strong>of</strong> risk management. A<br />
good understand<strong>in</strong>g <strong>of</strong> the hazard will help the risk management work more efficiently. But there are<br />
cases where the disaster reduction measures have been taken very well but do not have a well-def<strong>in</strong>ed<br />
hazard classification, such as Kathmandu.<br />
Figure 1-1 The risk management cycle show<strong>in</strong>g the sequence <strong>of</strong> assessment, response and education which<br />
is essential for successful disaster reduction (Smith 2001).<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 1
As the population grows the risk gets higher <strong>in</strong> many earthquake prone areas, especially <strong>in</strong> develop<strong>in</strong>g<br />
countries. Over 90 % <strong>of</strong> disaster related deaths occur among the two-thirds <strong>of</strong> the world’s population<br />
who live <strong>in</strong> the less developed countries and about three quarters <strong>of</strong> all the economic damage is conf<strong>in</strong>ed<br />
to the more developed countries (Smith 2001). Thus Asia, suffers greatly from natural disasters<br />
because <strong>of</strong> its large population, many <strong>of</strong> whom live <strong>in</strong> poverty and are concentrated <strong>in</strong> dense clusters<br />
<strong>in</strong> tectonically active zones or near low-ly<strong>in</strong>g coasts subject to cyclones and floods. Additionally, most<br />
earthquakes kill<strong>in</strong>g more than 100,000 people have occurred along the Himalayas, the Middle East and<br />
the Alps to the western Mediterranean and North Africa (Smith 2001). Casualty and the occurrence<br />
rate make Nepal one <strong>of</strong> the most vulnerable areas <strong>in</strong> the world. Above all, be<strong>in</strong>g a develop<strong>in</strong>g country,<br />
it is one <strong>of</strong> the places that need special attention regard<strong>in</strong>g the disaster issues.<br />
Many develop<strong>in</strong>g countries lack <strong>in</strong> fund<strong>in</strong>g for the studies that are needed for risk analysis and further<br />
studies. Many big organizations such as European Commission (EC) and United Nations (UN) have<br />
projects ongo<strong>in</strong>g <strong>in</strong> the area. Although the special attention needed is given, there is still need for new<br />
researches and implementations.<br />
One <strong>of</strong> the current research projects at <strong>ITC</strong> also focuses on risk management, and is entitled “Strengthen<strong>in</strong>g<br />
Local Authorities <strong>in</strong> Risk Management”. In this project Kathmandu and its surround<strong>in</strong>g regions<br />
are chosen as case study areas. This research falls <strong>in</strong>to the seismic hazard assessment section and also<br />
will be an <strong>in</strong>put for further analysis such as, build<strong>in</strong>g and population vulnerability estimation.<br />
As mentioned before risk management starts with the characterization <strong>of</strong> the hazard, which is seismic<br />
hazard analysis. For seismic hazard analysis and mapp<strong>in</strong>g a popular approach is to create zones. <strong>Seismic</strong><br />
zon<strong>in</strong>g can be dist<strong>in</strong>guished <strong>in</strong>to two: macro and microzon<strong>in</strong>g. <strong>Seismic</strong> macrozon<strong>in</strong>g consists <strong>of</strong><br />
divid<strong>in</strong>g the national territory <strong>in</strong>to several areas <strong>in</strong>dicat<strong>in</strong>g progressive levels <strong>of</strong> expected seismic <strong>in</strong>tensity<br />
for different return periods. These zones can be described <strong>in</strong> terms <strong>of</strong> peak acceleration values<br />
or any other strong ground motion parameter (Giard<strong>in</strong>i 1999). Macrozon<strong>in</strong>g, different then microzon<strong>in</strong>g<br />
focuses on small scales and <strong>in</strong>cludes probability. As seen below (Figure 1-2), the scale <strong>of</strong> the maps<br />
helps just to give an overall idea <strong>of</strong> the earthquake prone regions. For def<strong>in</strong><strong>in</strong>g earthquake source<br />
zones regional tectonics are used but they do not take <strong>in</strong>to account the regional geology. Earthquake<br />
catalogues are important <strong>in</strong> this assessment s<strong>in</strong>ce they po<strong>in</strong>t out the tectonically active regions.<br />
2<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
Figure 1-2 The seismic hazard map <strong>of</strong> Asia depict<strong>in</strong>g peak ground acceleration (PGA), given <strong>in</strong> units <strong>of</strong><br />
m/s2, with a 10% chance <strong>of</strong> exceedance <strong>in</strong> 50 years. The site classification is Rock. (Zhang, Yang et al.<br />
1992-1999)<br />
<strong>Seismic</strong> hazard microzon<strong>in</strong>g is used for more detailed zon<strong>in</strong>g, outl<strong>in</strong><strong>in</strong>g the parameters with a f<strong>in</strong>er<br />
spatial resolution and provid<strong>in</strong>g a description <strong>of</strong> the hazard parameter with higher accuracy and precision<br />
(Mayer-Rosa and Jimenez 2000). Microzon<strong>in</strong>g consists <strong>of</strong> record<strong>in</strong>g <strong>in</strong> detail all seismological,<br />
geological and hydrogeological parameters that may be needed <strong>in</strong> plann<strong>in</strong>g and implement<strong>in</strong>g a given<br />
project area at an appropriate scale for physical planners, urban designers, eng<strong>in</strong>eers and architects, or<br />
any other qualified user.<br />
For example civil eng<strong>in</strong>eers and urban planners use fragility curves that def<strong>in</strong>e the build<strong>in</strong>g type and<br />
number <strong>of</strong> storeys versus the peak ground acceleration values. Peak ground acceleration values come<br />
from response modell<strong>in</strong>g studies as an output data. Conclusively, these values create a l<strong>in</strong>k among the<br />
discipl<strong>in</strong>es. Problems that <strong>in</strong>crease the risk are ma<strong>in</strong>ly based on lack <strong>of</strong> attention to where and how<br />
settlements are built (UNDRO 1991). An unsuitable type <strong>of</strong> build<strong>in</strong>g with an unsuitable number <strong>of</strong><br />
storeys would result <strong>in</strong> serious damage and might collapse dur<strong>in</strong>g the expected earthquake. As a matter<br />
<strong>of</strong> fact, the decision for the location and the type <strong>of</strong> the settlements are an important factor to take <strong>in</strong>to<br />
account.<br />
Accord<strong>in</strong>g to the location decision, it is important to know the local soil and topographic conditions.<br />
The effect <strong>of</strong> local site conditions on the amplification <strong>of</strong> ground motions has long been recognized<br />
(Seed 1982). Depend<strong>in</strong>g on the subsurface characteristics, seismic waves might undergo amplification<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 3
and create more severe strong ground motions at the surface. Many earthquake prone cities are settled<br />
over very susceptible areas with young deposits such as Mexico City (Seed, Romo et al. 1987), Loma<br />
Prieta (Rodriguez-Marek and Bray 1999) and Kathmandu/Nepal. Hav<strong>in</strong>g a high potential for earthquakes<br />
and a susceptible local site environment, the situation <strong>in</strong> Kathmandu might turn a hazard <strong>in</strong>to a<br />
disaster <strong>in</strong> the future.<br />
In microzon<strong>in</strong>g the seismic hazard is assessed by means <strong>of</strong> expected response <strong>of</strong> the seismic waves for<br />
a given (scenario) earthquake for a specific area. S<strong>in</strong>ce the local soil site has significant effects on the<br />
seismic waves, “Ground <strong>Response</strong>” is one <strong>of</strong> the most important sections <strong>in</strong> microzon<strong>in</strong>g. Additionally,<br />
the subsurface and surface conditions <strong>in</strong> Kathmandu valley also are favourable for the occurrence<br />
<strong>of</strong> secondary hazards such as landslides, liquefaction, and fires.<br />
Ground response studies could be handled <strong>in</strong> different dimensions: one, two or three-dimensional.<br />
One-dimensional ground response analyses are based on the assumption that the ground surface and<br />
all material boundaries below the ground surface are horizontal and extend <strong>in</strong>f<strong>in</strong>itely <strong>in</strong> all lateral directions<br />
(Kramer 1996). The methods <strong>of</strong> one-dimensional ground response analysis are useful for level<br />
or gently slop<strong>in</strong>g sites with parallel material boundaries. The subsurface geology <strong>of</strong> Kathmandu Valley<br />
is also assumed to be suitable for one-dimensional ground response analysis, as Kathmandu valley is<br />
underla<strong>in</strong> by a thick deposit <strong>of</strong> alluvial and lacustr<strong>in</strong>e deposits. In addition, the assumption that the<br />
valley or another topographical feature could be one-dimensional is a major simplification.<br />
For one-dimensional calculations <strong>of</strong> the ground response, SHAKE s<strong>of</strong>tware is used widely s<strong>in</strong>ce<br />
1971(Ordonez 2002). Us<strong>in</strong>g SHAKE, the research problem then tends to focus on sensitivity analysis<br />
<strong>of</strong> the seismic response modell<strong>in</strong>g for Kathmandu city, which will try to def<strong>in</strong>e and simplify the <strong>in</strong>formation<br />
needed and evaluate it with<strong>in</strong> the concept <strong>of</strong> microzonation analysis. The ma<strong>in</strong> reason to<br />
focus on sensitivity analysis is to try to get more <strong>in</strong>formation for the valley, where there is lack<strong>in</strong>g <strong>in</strong><br />
data.<br />
1.2. Problem Statement<br />
In general terms, a seismic response analysis needs detailed geotechnical data, geology <strong>in</strong>formation,<br />
thickness <strong>of</strong> the subsurface geology pr<strong>of</strong>iles and a specific earthquake accelerogram file. More details<br />
on the required data will be expla<strong>in</strong>ed <strong>in</strong> the com<strong>in</strong>g section.<br />
Many countries, which are vulnerable to earthquakes, are lack<strong>in</strong>g <strong>in</strong> data for seismic response studies.<br />
Estimat<strong>in</strong>g the soil site response for strong ground motion is costly. In order to quantify the expected<br />
ground motion, we have to determ<strong>in</strong>e the manner <strong>in</strong> which the seismic signal is propagat<strong>in</strong>g through<br />
the surface. Propagation is particularly affected by the local geology and the geotechnical ground conditions.<br />
Borehole data, geotechnical, geological and geophysical parameters should be determ<strong>in</strong>ed.<br />
Such an <strong>in</strong>vestigation is not always easy to obta<strong>in</strong> hence you will need people with sufficient knowledge,<br />
tools, and laboratories which is not always the case for many develop<strong>in</strong>g countries.<br />
In Kathmandu the available data is not sufficient .To deal with this gap, numerical analysis could be<br />
used additionally to the exist<strong>in</strong>g data. For seismic response analysis the readily available data was used<br />
and then sensitivity analysis was applied. The aim <strong>of</strong> sensitivity analysis is to estimate the rate <strong>of</strong><br />
change <strong>in</strong> the output <strong>of</strong> a model with respect to changes <strong>in</strong> model <strong>in</strong>puts (Isukapalli 1999). A priority<br />
order for the <strong>in</strong>put parameters will be produced from the sensitivity assessment.<br />
4<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
1.3. Research Objectives<br />
<strong>Sensitivity</strong> analysis <strong>of</strong> ground response <strong>in</strong> SHAKE will provide <strong>in</strong> general, the priority <strong>of</strong> importance<br />
<strong>of</strong> the <strong>in</strong>put parameters and the estimation <strong>of</strong> output response values (acceleration, velocity etc.). To<br />
do that, several analyses will be applied for the available data <strong>in</strong> different comb<strong>in</strong>ations. Such an approach<br />
will try to give a generalized answer for the <strong>in</strong>put data lack<strong>in</strong>g and to improve the understand<strong>in</strong>g<br />
<strong>of</strong> the <strong>in</strong>formation content <strong>of</strong> geophysical data. The general research objectives can be expla<strong>in</strong>ed as<br />
follows:<br />
• To estimate the strong ground motions for soil site responses with the available data<br />
for Kathmandu valley.<br />
• To assess the sensitivity <strong>of</strong> the parameters that can be used to determ<strong>in</strong>e a microzonation<br />
study <strong>in</strong> Kathmandu valley.<br />
1.4. Research Methodology<br />
For seismic response model<strong>in</strong>g <strong>in</strong> the topic <strong>of</strong> seismic micro hazard assessment, the <strong>in</strong>formation<br />
needed <strong>in</strong> general is as follows;<br />
• Detailed geotechnical data (Shear wave velocity, unit weight, shear modulus and damp<strong>in</strong>g and<br />
modulus reduction curve <strong>in</strong>formation)<br />
• Detailed geology data available near the site. (Borehole log <strong>in</strong>formation with def<strong>in</strong>ed material<br />
and formations)<br />
• Digital seismic accelerograms (From a real earthquake or a synthetic one)<br />
• Depth to bedrock level<br />
• Ground water level<br />
In order to predict the seismic response it requires a lot <strong>of</strong> work <strong>in</strong> many discipl<strong>in</strong>es. The equipment<br />
and the knowledge are rarely found <strong>in</strong> many third world countries. It can be seen that the first threshold<br />
is to f<strong>in</strong>d out how much data is available <strong>in</strong> the region (Figure 1-3).<br />
If the <strong>in</strong>formation obta<strong>in</strong>ed from the consultancy <strong>of</strong>fices, agencies and governmental <strong>of</strong>fices is abundant,<br />
then the sensitivity analysis will be more accurate and site-depended. If not, then the exist<strong>in</strong>g<br />
literature <strong>in</strong>formation is assessed <strong>in</strong> the analysis. The topics that have been <strong>in</strong>vestigated from the literature<br />
are geotechnical data (shear wave velocity, depth etc.), characteristic earthquake <strong>of</strong> the region and<br />
subsurface geology studies.<br />
The ma<strong>in</strong> hypothesis <strong>in</strong> the assessment <strong>of</strong> sensitivity is that there is a clear relation between the various<br />
parameters. Overall, the first analysis will be look<strong>in</strong>g at specific parameters (E.g. shear wave velocity,<br />
unit weight) while keep<strong>in</strong>g the <strong>in</strong>put motion constant.<br />
The second analysis uses the constant parameter as a generalized pr<strong>of</strong>ile, which can be chosen from<br />
the exist<strong>in</strong>g boreholes <strong>in</strong> the Lalitpur municipality; Kathmandu study area. And test the range <strong>of</strong> responses<br />
related to the <strong>in</strong>put motions chosen.<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 5
The results <strong>of</strong> the analysis then are converted <strong>in</strong>to a range <strong>of</strong> accelerations that can be expected <strong>in</strong> the<br />
sites. These accelerations can be used to derive the response spectrum for the various parts <strong>of</strong> the study<br />
area. Then, it is possible to assess the values where the build<strong>in</strong>g frequency and the accelerations correspond.<br />
The resonance happens where the natural frequency <strong>of</strong> the build<strong>in</strong>gs and the frequency created<br />
on the soil site. Accord<strong>in</strong>gly, the predicted high damage sites can be def<strong>in</strong>ed from the areas with the<br />
same frequency with the build<strong>in</strong>gs. From the peak ground acceleration value, it is also possible to calculate<br />
the seismic <strong>in</strong>tensities us<strong>in</strong>g specific formulas.<br />
General methodology steps are as follows <strong>in</strong> the Figure 1-3,<br />
A. Literature survey<br />
B. Data acquisition<br />
C. Data process<strong>in</strong>g<br />
D. Data <strong>Analysis</strong><br />
1.4.1. Input data<br />
Under ideal conditions, a complete ground response study should <strong>in</strong>volve the rupture source modell<strong>in</strong>g<br />
(length, width and displacement <strong>of</strong> a rupture for a fault), the seismic wave behaviour to the top <strong>of</strong> the<br />
bedrock; (attenuation <strong>of</strong> the seismic waves <strong>in</strong> the bedrock site), the soil site wave propagation behaviour;<br />
(amplification <strong>of</strong> the seismic waves <strong>in</strong> the soil site) and the site specific strong ground motion<br />
records (Kramer 1996).Generally, the rupture source modell<strong>in</strong>g and the seismic wave behaviour to the<br />
top <strong>of</strong> the bedrock specifically for a site are hard to obta<strong>in</strong>. <strong>Soil</strong> site wave propagation and site specific<br />
or similar site’s strong ground motion could be used to study the ground response.<br />
To understand the soil site wave propagation behaviour, empirical or numerical methods can be used.<br />
One <strong>of</strong> the numerical methods deals with 1D response <strong>of</strong> soil columns where Shake2000 could be<br />
used. To apply this method the site should be horizontally layered. Input data that Shake2000 requires<br />
are; soil site geotechnical properties, depth and strong ground motion for the site. Then, the s<strong>of</strong>tware<br />
can run properly and give results for ground response.Nevertheless Shake2000 also needs detailed <strong>in</strong>formation.<br />
One <strong>of</strong> the unknown parameters is <strong>of</strong>ten the shear wave velocity <strong>of</strong> the various sediments <strong>in</strong><br />
the site and the way how this value changes with depth. There are expensive geophysical tools to <strong>in</strong>vestigate<br />
shear wave velocity, but the time and budget constra<strong>in</strong>ts <strong>of</strong> this research did not allow the<br />
geophysical <strong>in</strong>vestigations. In general, these <strong>in</strong>vestigations are hard to carry out <strong>in</strong> the framework <strong>of</strong><br />
an MSc study. Additionally, <strong>in</strong> Kathmandu this <strong>in</strong>formation was not readily available at the moment <strong>of</strong><br />
the fieldwork. So readily available data from boreholes and literature are used. To improve these assumptions<br />
a sensitivity analysis applied for the outcomes.<br />
6<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
Methodology<br />
A) Literature Review<br />
B) Data Acquisition<br />
(Field Survey)<br />
1. F<strong>in</strong>d<strong>in</strong>g out the similar earthquakes that<br />
can happen <strong>in</strong> the valley.<br />
2. Def<strong>in</strong><strong>in</strong>g scenario earthquakes.<br />
Accelerogram & seismogram record<br />
collection.<br />
3. Collection <strong>of</strong> borehole geotechnical<br />
parameter from boreholes.<br />
4. Collection shear wave velocity data.<br />
Creation <strong>of</strong> the access database file for the<br />
data collected from the consultancy <strong>of</strong>fices,<br />
municipalities etc.<br />
Field data<br />
sufficiency<br />
check.<br />
C) Data Process<strong>in</strong>g:<br />
Generalization <strong>of</strong> shear wave velocity and<br />
subsurface geology pr<strong>of</strong>iles us<strong>in</strong>g the field<br />
data and the exist<strong>in</strong>g ones.<br />
C) Data Process<strong>in</strong>g:<br />
Generalization <strong>of</strong> shear wave velocity and<br />
pr<strong>of</strong>iles <strong>of</strong> subsurface geology us<strong>in</strong>g<br />
the exist<strong>in</strong>g data.<br />
D) Data Analys<strong>in</strong>g<br />
(SHAKE analysis)<br />
1st analysis for constant <strong>in</strong>put motion and vary<strong>in</strong>g<br />
geotechnical parameters (Vs, unit weight etc)<br />
2nd analysis for constant geotechnical parameters<br />
(generalized pr<strong>of</strong>ile for a specific area: Lalitpur)<br />
and vary<strong>in</strong>g <strong>in</strong>put motions.<br />
Generation <strong>of</strong><br />
seismic <strong>in</strong>tensities.<br />
Output <strong>of</strong> analysis; range <strong>of</strong> acceleration values<br />
and their response spectrum.<br />
Figure 1-3 Flowchart <strong>of</strong> the methodology used <strong>in</strong> the research.<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 7
Here, the geophysical <strong>in</strong>vestigations that can be used to obta<strong>in</strong> the <strong>in</strong>put parameters will be discussed<br />
with short descriptions. In Table 1-1, given <strong>in</strong>vestigations techniques refer not only shear wave velocity<br />
but also to the other parameters (depth to bedrock, material thickness and types etc.)<br />
Investigations from surface.<br />
<strong>Seismic</strong> Methods<br />
Electrical Surveys<br />
Georadar Technique.<br />
Array Technique<br />
Spectral <strong>Analysis</strong> <strong>of</strong> Surface Waves<br />
Investigations us<strong>in</strong>g drill<strong>in</strong>g methods.<br />
Deep/Shallow Drill<strong>in</strong>g<br />
Crosshole Tomography<br />
Table 1-1 Investigation list <strong>in</strong> groups <strong>of</strong> different methods, from surface and by drill<strong>in</strong>g.<br />
The soil site wave propagation analysis could be done us<strong>in</strong>g one <strong>of</strong> the follow<strong>in</strong>g geophysical tools:<br />
• <strong>Seismic</strong> methods<br />
Travell<strong>in</strong>g from the source, a seismic wave reaches a po<strong>in</strong>t/surface and it creates the ground to move<br />
and oscillate. This can be measured <strong>in</strong> digital or analogue seismometers. This wave’s propagation can<br />
be analysed and, shear and primary wave velocities can be calculated us<strong>in</strong>g a seismometer. Us<strong>in</strong>g<br />
these reflection and refraction seismic methods seismometers: superficial deposit surveys, site <strong>in</strong>vestigation<br />
for eng<strong>in</strong>eer<strong>in</strong>g projects, boundaries, material types and elastic moduli can be measured or derived.<br />
Refraction seismology is a powerful and relatively cheap method for f<strong>in</strong>d<strong>in</strong>g the depths to approximately<br />
horizontal seismic <strong>in</strong>terfaces on all scales from site <strong>in</strong>vestigations to cont<strong>in</strong>ental studies<br />
(Musset and Khan 2000). It also yields the seismic velocities <strong>of</strong> the Rocks between <strong>in</strong>terfaces, which is<br />
important for ground response analysis. This method is also used and improved <strong>in</strong> microtremor studies,<br />
down hole shear wave velocity logs and P-wave refraction method. These methods result <strong>in</strong> shear<br />
wave velocity versus depth, after a couple <strong>of</strong> wave transformations (Louie, R. et al. 2003).<br />
Reflection seismology is <strong>of</strong>ten used to determ<strong>in</strong>e f<strong>in</strong>e details <strong>of</strong> the shallow structures, usually over<br />
small area. The resolution obta<strong>in</strong>able with reflection seismology makes it the ma<strong>in</strong> method used by oil<br />
exploration companies to map subsurface sedimentary structures. Oil companies’ <strong>in</strong>vestigations are<br />
generally sources for other purposes such as: the deep drill<strong>in</strong>gs for oil <strong>in</strong> Kathmandu are used to obta<strong>in</strong><br />
knowledge for deep lithology.<br />
• Electrical surveys<br />
In seismology electrical surveys could be done by us<strong>in</strong>g ground self-potential, resistivity surveys,<br />
ground and airborne electro-magnetic surveys and <strong>in</strong>duced polarization surveys. These surveys result<br />
<strong>in</strong> anomaly maps and pr<strong>of</strong>iles, position <strong>of</strong> ore-bodies and most important <strong>of</strong> all for this research: the<br />
depths to Rock layers. Additionally, Sand and Gravel deposits could be <strong>in</strong>vestigated.<br />
• Georadar<br />
Georadar is a portable digital subsurface sound<strong>in</strong>g radar. They are designed for solv<strong>in</strong>g a broad range<br />
<strong>of</strong> geotechnical, geological, environmental, eng<strong>in</strong>eer<strong>in</strong>g and other tasks such as bedrock depth determ<strong>in</strong>ation,<br />
water table determ<strong>in</strong>ation, anomalies or heterogeneities <strong>in</strong> the material, stratigraphic pr<strong>of</strong>iles,<br />
material layer<strong>in</strong>g etc. wherever non-destructive operational environmental monitor<strong>in</strong>g is needed<br />
(Christos, 2002).<br />
8<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
• Array method us<strong>in</strong>g ambient vibrations.<br />
The array method aims to lower the costs and the difficulties to undertake a local site effect us<strong>in</strong>g the<br />
borehole techniques and active seismic study with<strong>in</strong> a city. The array technique represents a cheap and<br />
fast method to measure shear wave velocities <strong>of</strong> the surficial sediments and the underly<strong>in</strong>g bedrock<br />
(K<strong>in</strong>d, Fah et al. 2003). The array technique for measur<strong>in</strong>g shear wave velocities is based on a theory<br />
developed by J. Capon 1969. It can be used <strong>in</strong> horizontally layered structures, like Kathmandu valley.<br />
• Spectral analysis <strong>of</strong> surface waves (SASW) method<br />
SASW is practical because surface waves are easy to generate. It is therefore suitable <strong>in</strong> areas <strong>of</strong> high<br />
seismic background noise (such as <strong>in</strong>dustrial and built-up areas), which a technique like seismic refraction<br />
cannot be used. SASW can be used to map bedrock topography, low/velocity/density zones,<br />
shear wave velocities and site stiffness (G max ). Also the bottom <strong>of</strong> lakes and the <strong>in</strong>formation about<br />
overburden stratigraphy can be gathered.<br />
• Deep or shallow drill<strong>in</strong>g with geotechnical <strong>in</strong>formation or lithological <strong>in</strong>formation<br />
Compar<strong>in</strong>g to the other surface measurements (Refraction, Reflection seismology etc.), this method<br />
relates the physical quantities more specifically. The general parameters that can be obta<strong>in</strong>ed from<br />
drill<strong>in</strong>g are: lithology, micr<strong>of</strong>ossils, permeability, porosity and fluids (Musset and Khan 2000). These<br />
measures can then be used to determ<strong>in</strong>e unit weight, shear modulus and shear wave velocity. Drill<strong>in</strong>g<br />
costs are generally high and the number <strong>of</strong> drill<strong>in</strong>gs needed is generally hard to obta<strong>in</strong>. Additionally,<br />
drill<strong>in</strong>gs for build<strong>in</strong>g purposes are common but they are shallow. Deep drill<strong>in</strong>gs are <strong>of</strong>ten for oil <strong>in</strong>vestigations<br />
and does not conta<strong>in</strong> geotechnical properties <strong>of</strong> soil but has lithology <strong>in</strong>formation.<br />
• Crosshole Tomography<br />
<strong>Seismic</strong> signals are generated <strong>in</strong> one borehole and are recorded by a str<strong>in</strong>g <strong>of</strong> geophones <strong>in</strong> a second<br />
borehole (Figure 1-4). By mathematical process<strong>in</strong>g <strong>of</strong> all the recorded data, a detailed velocity crosssection<br />
is obta<strong>in</strong>ed between the boreholes, which directly relates to materials quality. Fracture networks<br />
can also be followed, as they will slow down the velocity <strong>of</strong> seismic signals (Paul, 1998).<br />
The objective <strong>of</strong> the crosshole method is the 2D or 3D detail exploration between drill<strong>in</strong>gs.<br />
A great advantage <strong>of</strong> crosshole tomography is also a higher resolution <strong>of</strong> underground structures <strong>in</strong><br />
greater depths. P- and S-wave tomographic measurements are conducted to determ<strong>in</strong>e the structure,<br />
the elastic properties and the stress state <strong>of</strong> the Rock.<br />
Every tool mentioned <strong>in</strong> the list has its own difficulties to implement. In general terms, time, money<br />
and people with sufficient knowledge are needed to execute them. Under these circumstances, the<br />
fieldwork was focused on collect<strong>in</strong>g readily available data.<br />
The general <strong>in</strong>put parameters for SHAKE2000 are;<br />
• Geotechnical properties and depth <strong>in</strong>formation <strong>of</strong> the subsurface materials<br />
• Earthquake acceleration signal measured <strong>in</strong> Rock <strong>in</strong> a nearby site.<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 9
Figure 1-4 A representation <strong>of</strong> the crosshole tomography method. Left borehole consists <strong>of</strong> the transmission<br />
signals and the right one has the geophones, which receives the signals transmitted from the other<br />
borehole.<br />
Material properties should conta<strong>in</strong> shear wave velocity or shear modulus, damp<strong>in</strong>g ratio, unit weight<br />
and thickness. Water table depth is also another parameter that is needed to implement.<br />
Unit Weight<br />
Unit Weight parameter is the weight <strong>of</strong> a unit volume <strong>of</strong> soil is referred to as its unit weight. The units<br />
<strong>of</strong> unit weight will be force per unit volume, whereas the units <strong>of</strong> density are mass per unit volume.<br />
Unit weights can be calculated as follows;<br />
•<br />
•<br />
Dry Unit weight γ d =ρ d g kN/m 3<br />
Bulk Unit weight γ =ρ g kN/m 3<br />
• Saturated Unit Weight γ sat =ρ sat g kN/m 3<br />
•<br />
•<br />
Unit weight <strong>of</strong> water γ w =ρ w g kN/m 3<br />
Submerged unit weight γ =γ sat - γ w kN/m 3<br />
The gravitational acceleration “g” is generally taken as; 9.81 m/s 2 . Above calculations are <strong>in</strong> scientific<br />
<strong>in</strong>ternational units but for SHAKE2000 for unit weight pounds cubic feet is used.<br />
Shear Modulus<br />
Modulus <strong>of</strong> rigidity or shear modulus can be expla<strong>in</strong>ed us<strong>in</strong>g elastic properties <strong>of</strong> materials. The quantity<br />
µ, sometimes also called the rigidity, that is experimentally observed to relate stress and stra<strong>in</strong> accord<strong>in</strong>g<br />
to Hooke's law (Weisste<strong>in</strong>, 1999 ),<br />
[Stress]= µ[Stra<strong>in</strong>]<br />
It can also be expla<strong>in</strong>ed as, a measure <strong>of</strong> the resistance <strong>of</strong> the body to shear<strong>in</strong>g stra<strong>in</strong>s.<br />
Stress can be describes as, a force per unit area provided either by gravity or by the flow <strong>of</strong> viscous<br />
fluid. And stra<strong>in</strong> can be described as, the dimensionless parameter describ<strong>in</strong>g deformation. It can be<br />
thought <strong>of</strong> as the movement <strong>of</strong> one corner <strong>of</strong> a cubic box from its <strong>in</strong>itial position under a stress. In<br />
simple words, it is the relative change <strong>in</strong> shape and/or volume <strong>of</strong> a body.The concept <strong>of</strong> the formulas<br />
shown here are related with Elasticity <strong>in</strong> Mechanics, here the basics are given but the broader explanation<br />
is out <strong>of</strong> this research therefore it will not be expla<strong>in</strong>ed <strong>in</strong> detail. This parameter is used if shear<br />
wave velocity <strong>of</strong> the material is not known <strong>in</strong> SHAKE2000 and should have a unit <strong>of</strong> kilo pounds per<br />
feet.<br />
10<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
Shear wave velocity<br />
Just like the other waves (P, Love and Rayleigh etc.) shear wave velocities are also measured <strong>in</strong> the<br />
same way. An energy source (hammer, explosives etc.) is used to generate elastic waves <strong>in</strong> the ground.<br />
The signals are then collected and displayed on a seismograph. The advantage <strong>of</strong> this parameter on the<br />
other wave types is that it gives more <strong>in</strong>formation on the material type characteristics. And they depend<br />
on the shear strength <strong>of</strong> the material, which is the strength that supports build<strong>in</strong>gs and piles and<br />
keeps a ripp<strong>in</strong>g tooth from the cutt<strong>in</strong>g Rock (Geomatrix, 2003). The <strong>in</strong>formation on the shear wave<br />
velocities with density <strong>in</strong>formation and P-wave velocity also yields to the elastic constants, which is<br />
related to the magnitude <strong>of</strong> stra<strong>in</strong> response to the applied stress. The units <strong>of</strong> the results are generally<br />
<strong>in</strong> meters per second or feet per second.<br />
Thickness<br />
The soil pr<strong>of</strong>ile from the boreholes should have every layer’s thickness. The borehole logs usually<br />
have the soil boundaries obta<strong>in</strong>ed from the soil types and this can be measured, referr<strong>in</strong>g to thickness.<br />
The unit <strong>of</strong> thickness should be <strong>in</strong> feet for SHAKE2000 calculations.<br />
Damp<strong>in</strong>g ratio<br />
Damp<strong>in</strong>g properties <strong>of</strong> soils are also used for each soil type and layer <strong>in</strong> the soil pr<strong>of</strong>ile <strong>of</strong><br />
SHAKE2000. In real life, energy is lost by friction, heat generation, air resistance or other physical<br />
mechanisms. Damp<strong>in</strong>g acts as a force oppos<strong>in</strong>g vibration and decreases the amplitudes <strong>of</strong> the free vibrations<br />
(US Army Corps <strong>of</strong> Eng<strong>in</strong>eers, 2001). The damp<strong>in</strong>g ratio is calculated by:<br />
ξ = c / 2√ k m<br />
“ξ “ is the damp<strong>in</strong>g ratio coefficient, “c” is the viscous damp<strong>in</strong>g coefficient, “k” gives the stiffness and<br />
”m” is the mass. The “2√ k m “ gives the critical damp<strong>in</strong>g coefficient. The reason for us<strong>in</strong>g systems<br />
with variable damp<strong>in</strong>g <strong>in</strong>formation is to <strong>in</strong>corporate non-l<strong>in</strong>ear soil behaviour (Ordonez, 2002). It is<br />
expressed <strong>in</strong> decimals.<br />
The earthquake <strong>in</strong>put signal ideally should be available from a recent earthquake that happened <strong>in</strong> a<br />
nearby site. This requires the availability <strong>of</strong> a network <strong>of</strong> accelerometers. Unfortunately for Kathmandu<br />
there is no such network <strong>in</strong> operation. As an alternative an <strong>in</strong>put signal could be chosen from<br />
the vast database that is already <strong>in</strong> the s<strong>of</strong>tware or on the Internet and implemented us<strong>in</strong>g an ASCII<br />
coded accelerogram file.<br />
1.4.2. Data collection<br />
From 8 th <strong>of</strong> September till 3 rd <strong>of</strong> October 2003 data was collected <strong>in</strong> many private and governmental<br />
<strong>of</strong>fices <strong>in</strong> Kathmandu and its surround<strong>in</strong>g places. The ma<strong>in</strong> partners were NSET (National Society for<br />
Earthquake Technology) and ICIMOD (International Center for Integrated Mounta<strong>in</strong> Development)<br />
S<strong>in</strong>ce there were very few deep drill<strong>in</strong>gs with geotechnical <strong>in</strong>formation available for the Kathmandu<br />
area (Piya, 2004), most emphasis was given to on f<strong>in</strong>d<strong>in</strong>g shallow boreholes with geotechnical <strong>in</strong>formation<br />
and deep boreholes with lithological descriptions. Additionally, the accelerogram files and<br />
suggestions on similar 1934 (M=8.4) earthquake <strong>in</strong>formation. Similar earthquake <strong>in</strong>formation would<br />
help to choose a correct <strong>in</strong>put signal for the analysis. The organizations that were visited for the collection<br />
<strong>of</strong> borehole data are listed <strong>in</strong> Table 1-2.<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 11
Governmental <strong>of</strong>fices<br />
University<br />
Organizations<br />
Private Consultancies<br />
Abbreviations<br />
KMC DMC<br />
MLSC<br />
MK<br />
DMG<br />
IOE, TU<br />
DWIDP<br />
JICA<br />
ICIMOD<br />
NSET<br />
Nissaku Co -<br />
Nippon Koei -<br />
Geotech -<br />
Silt -<br />
East Drill<strong>in</strong>g -<br />
Tech -<br />
Name<br />
Kathmandu Metropolitan City<br />
Disaster Management Center<br />
Municipality <strong>of</strong> Lalitpur submetropolitan<br />
city<br />
Municipality <strong>of</strong> Kathmandu<br />
Department <strong>of</strong> m<strong>in</strong>es and geology<br />
(Remote Sens<strong>in</strong>g Laboratory<br />
and National Seismology<br />
Centre)<br />
Purbachar University<br />
Institute <strong>of</strong> Eng<strong>in</strong>eer<strong>in</strong>g- Tribhuvan<br />
University<br />
Department <strong>of</strong> Water Induced<br />
Disaster<br />
Japan International Cooperation<br />
Agency<br />
International Center For Integrated<br />
Mounta<strong>in</strong> Development<br />
National Society for Earthquake<br />
Technology<br />
Table 1-2 The names and abbreviations <strong>of</strong> the organizations contacted <strong>in</strong> the fieldwork.<br />
From the various organisations the follow<strong>in</strong>g types <strong>of</strong> <strong>in</strong>formation were collected:<br />
• Borehole descriptions (from different consultancies and agencies- 6 shallow with geotechnical<br />
<strong>in</strong>formation and 11 deep drill<strong>in</strong>gs with lithology <strong>in</strong>formation)(Table 1-3)(Figure 1-5)<br />
• Digital GIS maps (geology, l<strong>in</strong>eaments etc)<br />
• Reports (JICA study and reports that are related to Kathmandu valley geology, characteristics<br />
<strong>of</strong> soil etc)<br />
• Articles<br />
12<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
• Hard copy maps <strong>of</strong> the eng<strong>in</strong>eer<strong>in</strong>g geology <strong>of</strong> Kathmandu valley, seismic hazard and macroseismic<br />
epicentral maps<br />
• Meet<strong>in</strong>gs for discussion on SPT-n value correction and SHAKE s<strong>of</strong>tware.<br />
• Reports from Himalayan region for def<strong>in</strong><strong>in</strong>g similar earthquakes for the region<br />
Deep Boreholes<br />
Shallow Boreholes<br />
Borehole ID Location Borehole<br />
ID<br />
Location<br />
B1 Harisidhi C - 40 UNDP Build<strong>in</strong>g Pulchok, Lalitpur<br />
B 24 Shanta Bhawan C-296 Kantipur Television network P.Ltd Pulchok,<br />
Lalitpur<br />
B 25 Surendra Bhawan C-291 Lalitpur Bisalbazar, Communication Complex<br />
Pulchok, Lalitpur<br />
B 23 Patan C - 288 Jawalakhel<br />
AG 68 Patan Hospital SPT - 6 Lele<br />
BHD 3 B & B Hospital Guarkhu SPT - 39 Dhobighat<br />
DMG 13<br />
P 37<br />
P 29<br />
PR 16<br />
SPT 25<br />
Balkumari, Lalitpur<br />
Interknit <strong>in</strong>dustries<br />
Hotel Himalaya<br />
Nurs<strong>in</strong>g Campus, Sanepa<br />
Khumaltar<br />
Table 1-3 The borehole names and locations that are used <strong>in</strong> the analysis (Wald, 1999)<br />
1.4.3. Data organization<br />
Many people are work<strong>in</strong>g on the Valley’s hazard issues not only on seismic but also floods and landslides<br />
etc. The data collected <strong>in</strong> Kathmandu resulted <strong>in</strong> 90 <strong>in</strong>dividual pieces <strong>of</strong> <strong>in</strong>formation obta<strong>in</strong>ed<br />
from 72 different contacts. For both the data and the organisations it was decided to store the metadata<br />
us<strong>in</strong>g Micros<strong>of</strong>t Access, <strong>in</strong> a database.<br />
Contacts database has columns titled: <strong>in</strong>formation topic, first name, surname, company name, title,<br />
home address, home and work phone, email, fax number and mobile phone number. The contact also<br />
had a unique identification number.<br />
For the data collected each item has a metadata word file describ<strong>in</strong>g the source and the type <strong>of</strong> data<br />
<strong>in</strong>formation. The database <strong>of</strong> the metadata has unique identifiers and the related contacts identifiers<br />
and the name <strong>of</strong> the data collected. In Access s<strong>of</strong>tware it is easy to make queries for example if you are<br />
<strong>in</strong>terested <strong>in</strong> only the emails and the items collected, you can easily create the query us<strong>in</strong>g a wizard.<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 13
W<br />
N<br />
S<br />
E<br />
Borehole Locations <strong>in</strong> Lalitpur<br />
Sub-metropolitan city.<br />
SPT_39<br />
PR_16<br />
#Y #Y#Y #<br />
#<br />
#Y#<br />
#<br />
#Y<br />
#<br />
#Y<br />
#<br />
#Y<br />
B_25<br />
B_24<br />
AG_68<br />
SPT_6<br />
#<br />
#Y#Y<br />
P_29<br />
C_40<br />
C_296<br />
B_23<br />
#<br />
BHD_3<br />
#<br />
DMG_13 #Y<br />
#<br />
#Y #Y<br />
SPT_25<br />
P_37<br />
#<br />
#<br />
#Y#Y<br />
Legend<br />
#Y Borehole ID's<br />
Boundary <strong>of</strong> Lalitpur<br />
3000 0 3000 6000 Meters<br />
1-5 The borehole names and locations that are used <strong>in</strong> the analysis<br />
Figure<br />
The metadata <strong>in</strong>cluded the name <strong>of</strong> data, ID number <strong>in</strong> the database, theme, abstract, keywords, type<br />
<strong>of</strong> data etc. The numbers <strong>of</strong> the word files represents the ID number for the data <strong>in</strong> the data collected<br />
database, which can be also l<strong>in</strong>ked to the contact ID (Figure 1-6). The database files can be found <strong>in</strong><br />
the annexes section <strong>of</strong> the thesis.<br />
1.4.4. Structure <strong>of</strong> the Thesis<br />
The structure <strong>of</strong> the thesis <strong>in</strong> short explanations is as follows:<br />
1. Chapter one gives a general context <strong>of</strong> the study <strong>in</strong>clud<strong>in</strong>g the <strong>in</strong>troduction, problem statement, and<br />
research objectives.<br />
2. Chapter two presents the literature review on the topics from seismic microzon<strong>in</strong>g to sensitivity<br />
analysis.<br />
3. Chapter three gives an overview <strong>of</strong> the s<strong>of</strong>tware used; Shake2000.<br />
4. Chapter four presents the study area <strong>in</strong>clud<strong>in</strong>g geology and seismicity.<br />
5. Chapter five gives the results <strong>of</strong> the seismic response analysis.<br />
14<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
6. Chapter six the assessment <strong>of</strong> the result <strong>of</strong> the sensitivity analysis, the response spectrum and seismic<br />
<strong>in</strong>tensity map.<br />
7. Chapter seven will be present<strong>in</strong>g the results <strong>of</strong> the study and the discussions about them.<br />
Figure 1-6 Figure show<strong>in</strong>g the contacts, data collected and metadata relation diagram.<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 15
2. Literature Review<br />
<strong>Sensitivity</strong> analysis can be applied to many discipl<strong>in</strong>es from politics to physics. In geological hazard<br />
studies this also can be done for the <strong>in</strong>put parameters for seismic response models, which is selected<br />
for this study. If it is deducted from the wider concepts <strong>of</strong> the seismic hazard assessment, the ma<strong>in</strong><br />
branches <strong>in</strong>clude:<br />
• <strong>Seismic</strong> Hazard Assessment<br />
• <strong>Seismic</strong> Microzonation<br />
• Ground <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong><br />
• <strong>Sensitivity</strong> <strong>Analysis</strong><br />
To give a summary <strong>of</strong> the literature review <strong>of</strong> these topics, the terms and concepts that are go<strong>in</strong>g to be<br />
dealt <strong>in</strong> the review should be clarified.<br />
Although, <strong>in</strong> this research the focus is on sensitivity analysis, it is also based on a broader concept <strong>of</strong><br />
<strong>Seismic</strong> hazard assessment. <strong>Seismic</strong> hazard assessment <strong>in</strong>volves the quantitative evaluation <strong>of</strong> ground<br />
shak<strong>in</strong>g hazards (primary hazard; earthquakes damage to the site and secondary hazards such as: fires,<br />
landslides and liquefaction etc) at a specific location. The analysis can be taken <strong>in</strong> two ways; determ<strong>in</strong>istically<br />
and probabilistically. The determ<strong>in</strong>istic approach uses an accepted earthquake scenario,<br />
whereas the probabilistic approach quantifies the rate (or probability) <strong>of</strong> exceed<strong>in</strong>g various groundmotion<br />
levels at a site, given all possible earthquakes (Field 2001).<br />
This research follows a determ<strong>in</strong>istic approach and will be based on earthquake scenarios. In seismic<br />
microzonation studies, seismological, geological, hydrogeological, topographical and geotechnical<br />
data are necessary to implement the analysis. Microzonation studies provide important <strong>in</strong>formation on<br />
the parameters that may be needed <strong>in</strong> plann<strong>in</strong>g and implement<strong>in</strong>g a project done by physical planners,<br />
urban designers, eng<strong>in</strong>eers, architects etc. Apart from compil<strong>in</strong>g <strong>in</strong>put data, estimation <strong>of</strong> the ground<br />
response takes place, which is one <strong>of</strong> the most important sections <strong>in</strong> microzonation.<br />
Second, estimation <strong>of</strong> the ground response will be applied <strong>in</strong> the research focus<strong>in</strong>g on the soil site effects.<br />
To model ground response, two ma<strong>in</strong> effects should be considered, soil site and topography effects.<br />
<strong>Soil</strong> site effects are much more commonly <strong>in</strong>vestigated, then the topographical effects. The ma<strong>in</strong><br />
reason for that is usually, the urbanization takes place where s<strong>of</strong>t soils develop, such as coastal pla<strong>in</strong>s<br />
and river valleys. On the other hand, topographic effects are also very important for urban areas, s<strong>in</strong>ce<br />
settlements are generally on bas<strong>in</strong>s where there is a great amount <strong>of</strong> amplification due to topography.<br />
Above all, topographic amplification is very complex and needs 3D analysis <strong>in</strong> order to have better<br />
accuracy where, soil site effects could be <strong>in</strong>vestigated us<strong>in</strong>g 1D models. S<strong>in</strong>ce more population and<br />
more risk <strong>in</strong>volved on the soil site, the estimation <strong>of</strong> these effects was more popular for the scientific<br />
community. So far the destructive earthquakes like Mexico 1985, Kobe 1995 and Turkey 1999 took<br />
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place where the ground responses were amplified because <strong>of</strong> the soil site properties. <strong>Soil</strong> site properties<br />
def<strong>in</strong>e the seismic wave behaviour under the site. The waves can be affected <strong>in</strong> such a way that<br />
when they reach the surface, they create more shak<strong>in</strong>g. Macroseismic observations have demonstrated<br />
very clearly that the damag<strong>in</strong>g effects associated with such s<strong>of</strong>t deposits may lead to local <strong>in</strong>tensity<br />
<strong>in</strong>crements as large as 2, <strong>in</strong> extreme cases even 3 degrees on the MM (Modified Mercalli) or<br />
MSK/EMS (Medvedev, Sponheuer and Karnik ; 1964 scale) scale (Irikura 1983; Lacave, Bard et al.<br />
2002).<br />
For the <strong>in</strong>vestigations <strong>of</strong> the soil site effects, the methods used are empirical, theoretical or semiempirical.<br />
For this research, widely used s<strong>of</strong>tware (SHAKE2000) is applied and one-dimensional<br />
(horizontally layered) responses <strong>of</strong> soil layers are calculated us<strong>in</strong>g numerical methods.<br />
F<strong>in</strong>ally, SHAKE2000 needs specific geotechnical <strong>in</strong>puts such as; <strong>in</strong>put signal (scenario earthquake)<br />
shear wave velocity and soil thickness. The overall research problem is focused on analys<strong>in</strong>g the sensitivity<br />
<strong>of</strong> these <strong>in</strong>put parameters. For that, one <strong>of</strong> the parameters is kept constant and others vary <strong>in</strong> realistic<br />
values. Not so many sensitivity analyses have taken place for the general <strong>in</strong>put parameters for<br />
ground response modell<strong>in</strong>g so far <strong>in</strong> literature. Though, there is a great demand from eng<strong>in</strong>eers and<br />
planners to be able to conduct earthquake resistant build<strong>in</strong>gs for high-risk areas. The outcome <strong>of</strong> the<br />
sensitivity analysis and the research provides range <strong>of</strong> values for the <strong>in</strong>put parameters and their properties.<br />
The general term<strong>in</strong>ology and the overall research concept have been <strong>in</strong>troduced above. In the<br />
com<strong>in</strong>g sections the various components will be treated more <strong>in</strong> detail. Different views and newly advised<br />
ideas will be presented <strong>in</strong> a short summary.<br />
2.1. Overview Of Methods For <strong>Seismic</strong> Hazard Assessment<br />
2.1.1. <strong>Seismic</strong> Hazard Assessment<br />
<strong>Seismic</strong> hazard analyses <strong>in</strong>volve the quantitative estimation <strong>of</strong> ground shak<strong>in</strong>g hazards at a particular<br />
site (Kramer 1996). On the other hand <strong>in</strong> the Global <strong>Seismic</strong> Hazard Assessment Program (1992-<br />
1999), seismic hazard analyses were def<strong>in</strong>ed as “the assessment <strong>of</strong> seismic hazard measures our understand<strong>in</strong>g<br />
<strong>of</strong> the recurrence <strong>of</strong> earthquakes <strong>in</strong> seismogenic sources” (Giard<strong>in</strong>i 1999). Here, the probability<br />
<strong>of</strong> earthquakes was mentioned to be <strong>in</strong>volved <strong>in</strong> the overall assessment. Occasionally, the division<br />
between the determ<strong>in</strong>istic and the probabilistic studies still cont<strong>in</strong>ues to take place <strong>in</strong> studies. <strong>Seismic</strong><br />
hazard assessment could be determ<strong>in</strong>istic or probabilistic; the two ways could also be used for one<br />
study. The decision is more depends on the approach and available data for the region.<br />
Initially, for the probabilistic approach (PSHA) first formed by Cornell (1968), the follow<strong>in</strong>g procedures<br />
are applied. First, the del<strong>in</strong>eation <strong>of</strong> earthquake source regions <strong>in</strong> terms <strong>of</strong> their boundaries, level<br />
<strong>of</strong> activity and upper <strong>in</strong>tensity threshold are applied (Step 1 <strong>in</strong> the Figure 2-1). Second part is the determ<strong>in</strong>ation<br />
<strong>of</strong> the macroseismic <strong>in</strong>tensity changes with distance, magnitude, focal length and ground<br />
conditions (Step 2-3; Particularly <strong>in</strong> the direction from the source region to the site) Third, applications<br />
<strong>of</strong> a theoretical model to the calculation <strong>of</strong> the seismic hazard at the site under study (Step 4)<br />
(Schenk 1996).<br />
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Figure 2-1The four steps <strong>of</strong> probabilistic seismic hazard analysis (Kramer 1996).<br />
Probabilistic hazard assessment maps are generally called “peak acceleration (%g) with %10 probability<br />
<strong>of</strong> exceedance <strong>in</strong> 50 years “ (Figure 2-2). In simple words, the name refers to the chance <strong>of</strong> an<br />
earthquake to happen (probability percentage (2, 10 etc.)) <strong>in</strong> 50 years. Cornell (1968) added that even<br />
well def<strong>in</strong>ed s<strong>in</strong>gle numbers such as the “expected lifetime maximum “ or “ 50-year” <strong>in</strong>tensity are <strong>in</strong>sufficient<br />
to give the eng<strong>in</strong>eer an understand<strong>in</strong>g <strong>of</strong> how quickly the risk decreases as the ground motion<br />
<strong>in</strong>tensity <strong>in</strong>crease. This also still raises the questions for the convenient parameter, to use for the<br />
maps and visualization <strong>of</strong> the strong ground motion analysis.<br />
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Figure 2-2 A probabilistic seismic hazard map show<strong>in</strong>g U.S. for the peak acceleration (%g) with<br />
%10 probability <strong>of</strong> exceedance <strong>in</strong> 50 years (USGS 2003).<br />
One <strong>of</strong> the recent discussions related to the probabilistic approach was on the selection <strong>of</strong> the proper<br />
ground motion parameter <strong>in</strong> calculations and representation <strong>of</strong> the maps. As can be seen form the Figure<br />
2 the title <strong>of</strong> the map is a bit complex <strong>in</strong> style. For representations <strong>of</strong> the maps the ground motion<br />
parameters are obta<strong>in</strong>ed <strong>in</strong> acceleration, velocity and displacement. The first practices were mostly <strong>in</strong><br />
favour <strong>of</strong> acceleration values. Then, velocity values were suggested for use as well. Regard<strong>in</strong>g to these<br />
discussions, E.H. Field (2001) suggested us<strong>in</strong>g the response spectral acceleration, which is another<br />
parameter that can be derived from acceleration values.<br />
Traditionally, peak ground acceleration (PGA) has been used to quantify ground motion <strong>in</strong> probabilistic<br />
seismic hazard assessment. It is used <strong>in</strong> liquefaction analyses and to def<strong>in</strong>e build<strong>in</strong>g codes. PGA<br />
has been an important parameter s<strong>in</strong>ce the earthquake and civil eng<strong>in</strong>eers were us<strong>in</strong>g this value for<br />
creat<strong>in</strong>g the build<strong>in</strong>g codes. On the other hand, it is suggested that <strong>Response</strong> Spectral Acceleration<br />
(SA), should be used. SA gives the maximum acceleration experienced by a damped, s<strong>in</strong>gle-degree<strong>of</strong>-freedom<br />
oscillator (a crude representation <strong>of</strong> build<strong>in</strong>g response) (Field 2001).<br />
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When comput<strong>in</strong>g the seismic response on a structure, it would be better to start simplify<strong>in</strong>g them to a<br />
s<strong>in</strong>gle degree <strong>of</strong> freedom system (Figure 2-3). The SDOF oscillator may be regarded as the simplest<br />
model <strong>of</strong> a build<strong>in</strong>g that is separated from the basement.<br />
Figure 2-3 The illustration <strong>of</strong> the s<strong>in</strong>gle degree <strong>of</strong> freedom systems.<br />
In Figure 2-3, the rigid mass M represents the build<strong>in</strong>g and the l<strong>in</strong>ear spr<strong>in</strong>g k represents the separation<br />
bear<strong>in</strong>g. Damp<strong>in</strong>g may be accounted for by a viscous damp<strong>in</strong>g coefficient; dashpot c. Com<strong>in</strong>g back to<br />
the discussions on the appropriate parameter, they still go<strong>in</strong>g on but for many approaches peak acceleration<br />
values are the popular ones.<br />
The second approach <strong>of</strong> the seismic hazard assessment, a basic “Determ<strong>in</strong>istic <strong>Seismic</strong> Hazard <strong>Analysis</strong><br />
(DSHA)” is a relatively simple process that is useful especially where tectonic features are reasonably<br />
active and well def<strong>in</strong>ed. The focus is generally on determ<strong>in</strong><strong>in</strong>g the Maximum Credible Earthquake<br />
(MCE) motion at the site. The steps <strong>in</strong> the process are as follows:<br />
1. Identify nearby seismic source zones - these can be specific faults or distributed sources<br />
(Step 1 <strong>in</strong> Figure 2-4)<br />
2. Identify distance to site for each source (nearby distributed sources are a problem) (Step 2)<br />
3. Determ<strong>in</strong>e magnitude and other characteristics (ie. fault length, recurrence <strong>in</strong>terval) for each<br />
source (Step 3)<br />
4. Establish response parameter <strong>of</strong> <strong>in</strong>terest for each source as a function <strong>of</strong> magnitude, distance,<br />
soil conditions, etc., us<strong>in</strong>g the average <strong>of</strong> several ground motion attenuation relationships<br />
(Step 3)<br />
5. Tabulate values from each source and use the largest value (Step 4) (Mah<strong>in</strong> and Rogers<br />
1999)<br />
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Figure 2-4 The determ<strong>in</strong>istic seismic hazard assessment diagram <strong>in</strong> steps (Kramer 1996).<br />
In general discussion on determ<strong>in</strong>istic seismic hazard assessment, the criticism on Maximum Credible<br />
Earthquake (MCE) was on the determ<strong>in</strong>ation was basically depended on the expert, which may and<br />
would lead to a subjective result <strong>in</strong> most <strong>of</strong> the cases. Then, another term has been raised, which is<br />
“Safety Evaluation Earthquake” (SEE). This term differs from a MCE that might be considered for the<br />
area, <strong>in</strong> that it takes <strong>in</strong>to account the types <strong>of</strong> structures which are vulnerable to the various earthquake<br />
hazards <strong>in</strong> the area, as well as the risk that is acceptable to the community <strong>in</strong> the light <strong>of</strong> other social<br />
considerations (Bolt 1994).<br />
The discussions <strong>of</strong> seismic hazard assessment are also focused on the selection between the approaches<br />
(determ<strong>in</strong>istic and probabilistic). For example Panza et al. (2003) have outl<strong>in</strong>ed that “the<br />
probabilistic approach, unavoidably based on rough assumptions and models (e.g. recurrence and attenuation<br />
laws), can be mislead<strong>in</strong>g as it cannot take <strong>in</strong>to account, with satisfactory accuracy, some <strong>of</strong><br />
the most important aspects which characterize the critical motion for base-isolated and standard structures<br />
(E.g. rupture process, directivity and site effects are not <strong>in</strong>volved <strong>in</strong> probabilistic approach)<br />
(Decan<strong>in</strong>i, Mollsioli et al.; Panza, Romanelli et al. 2003). This is evidenced by the comparison <strong>of</strong> recent<br />
record<strong>in</strong>gs with the values predicted by the probabilistic methods. We prefer a scenario-based,<br />
determ<strong>in</strong>istic approach <strong>in</strong> view <strong>of</strong> the limited seismological data, <strong>of</strong> the local irregularity <strong>of</strong> the occurrence<br />
<strong>of</strong> strong earthquakes, and <strong>of</strong> the multiscale seismicity model..” The authors <strong>of</strong> this paper are <strong>in</strong><br />
favour <strong>of</strong> determ<strong>in</strong>istic approach and highlight the important aspects that are miss<strong>in</strong>g <strong>in</strong> the probabilistic<br />
approach such as rupture process (rupture front (The <strong>in</strong>stantaneous boundary between the slipp<strong>in</strong>g<br />
and locked parts <strong>of</strong> a fault dur<strong>in</strong>g an earthquake) direction and velocity; and site effects which have<br />
great <strong>in</strong>fluence on the shak<strong>in</strong>g (soil site type or topography type)).<br />
When we compare the two approaches, both <strong>of</strong> them have their advantages and disadvantages. Many<br />
adaptations have been published to reduce their disadvantages. For determ<strong>in</strong>istic approaches one <strong>of</strong> the<br />
recurrent criticisms was that they make use <strong>of</strong> a controll<strong>in</strong>g earthquake (usually the maximum to have<br />
occurred with<strong>in</strong> a given time and space doma<strong>in</strong>) <strong>in</strong>stead <strong>of</strong> frequency <strong>of</strong> earthquake occurrence. Oro-<br />
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zova and Suhadolc (1999) proposed a method to overcome this criticism and at the same time ma<strong>in</strong>ta<strong>in</strong><br />
the advantages <strong>of</strong> the determ<strong>in</strong>istic approach, which are clear and realistic estimation <strong>of</strong> eng<strong>in</strong>eer<strong>in</strong>g<br />
parameters needed <strong>in</strong> the calculation <strong>of</strong> <strong>Seismic</strong> Risk. They have used a determ<strong>in</strong>istic method for seismic<br />
hazard assessment where they have replaced the fixed controll<strong>in</strong>g scenario earthquake with earthquake<br />
frequency.<br />
2.1.2. <strong>Seismic</strong> Microzon<strong>in</strong>g<br />
After hav<strong>in</strong>g looked at the broader concept <strong>of</strong> <strong>Seismic</strong> Hazard <strong>Analysis</strong>, this part focuses on more detailed<br />
studies, which are carried out for microzonation. S<strong>in</strong>ce the method for this research falls under<br />
the microzonation type, the general approaches <strong>of</strong> microzonation will be treated and illustrated by examples<br />
and several discussion topics will be po<strong>in</strong>ted out.<br />
A microzonation study should <strong>in</strong>clude the two effects that have the greatest <strong>in</strong>fluence on the seismic<br />
wave behaviour, which are site and topographic amplification. Topographic amplification can be observed<br />
<strong>in</strong> <strong>in</strong>strumental studies on the ground motion amplitudes and frequency content. Some <strong>of</strong> the<br />
studies can be found <strong>in</strong> Geli et al (1988) and Faccioli (1991). Examples <strong>of</strong> topographic structures that<br />
can have considerable effects on the damage are hill tops and ridge crests which have a <strong>in</strong>creas<strong>in</strong>g effect<br />
on the one hand side <strong>of</strong> valleys and bases <strong>of</strong> hills on the other hand which have a de-amplification<br />
effect (Lacave, Bard et al. 2002) (Figure 2-5).<br />
Figure 2-5 Diagram show<strong>in</strong>g the topographic and soil site effects. <strong>Seismic</strong> waves travel through the settlements<br />
pass<strong>in</strong>g the Rock site and soil site. For both the soil site and the Rock hill top there is generally a<br />
referr<strong>in</strong>g topographic effect such as hill top, ridge and bas<strong>in</strong> effects.<br />
However, the number <strong>of</strong> <strong>in</strong>strumental studies about topographic effects is too low to derive any statistical<br />
relations from the exist<strong>in</strong>g data. That is also one <strong>of</strong> the reasons that site effects are chosen for this<br />
research. Lalitpur city is <strong>in</strong> Kathmandu Valley, it forms a bas<strong>in</strong> surrounded by the hilly terra<strong>in</strong>, where<br />
the so-called bas<strong>in</strong> effects should be considered. The shape <strong>of</strong> a bas<strong>in</strong> is curvature and filled with s<strong>of</strong>t<br />
sediments, which can trap some <strong>of</strong> the body waves and transform to surface waves. Surface waves can<br />
22<br />
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create stronger shak<strong>in</strong>g and make longer the duration <strong>of</strong> the shak<strong>in</strong>g. The simple irregularities (Figure<br />
2-6; a, triangular wedge) can be solved us<strong>in</strong>g idealized problems (Aki, 1988)<br />
Figure 2-6 Two simple topographic irregularities. (a) a triangular wedge (b) approximation <strong>of</strong><br />
real surface at rough and crest by wedges (Faccioli, 1991)<br />
There are two examples shown below with different approaches <strong>of</strong> seismic microzonation. The first<br />
one uses many geotechnical analysis results to create a zonation map. The method is more conventional<br />
then the second one. Second one, additional to the several geotechnical <strong>in</strong>formation gathered,<br />
they give rank<strong>in</strong>g to each set <strong>of</strong> <strong>in</strong>formation <strong>in</strong> a geographical <strong>in</strong>formation system.<br />
A good example <strong>of</strong> seismic microzonation studies is presented by Topal et. al. (2003) who studied the<br />
microzonation for Yenişehir settlement <strong>in</strong> Turkey. They have performed detailed geological, hydrogeological<br />
and geotechnical studies for the assessment <strong>of</strong> the foundation conditions <strong>of</strong> the present and<br />
future settlement areas <strong>of</strong> Yenişehir. The geotechnical evaluation <strong>in</strong>cluded trial pitt<strong>in</strong>g, drill<strong>in</strong>g, <strong>in</strong> situ<br />
test<strong>in</strong>g and laboratory test<strong>in</strong>g. Borehole logs, <strong>in</strong>dex properties <strong>of</strong> soils, standard penetration test results<br />
and ground water level measurements were used for activity and liquefaction assessments <strong>of</strong> the foundation<br />
material. The study gave some advice on the conditions <strong>of</strong> the soil. They did not expect any<br />
landslide or flood problems; on the other hand, the northern sector was characterized by Clayey soils<br />
with high expansion. Accord<strong>in</strong>g to the article, <strong>in</strong> this area shallow foundations should be avoided and<br />
build<strong>in</strong>gs with basement floors should be preferred. And <strong>in</strong> the southern sector, medium to loose saturated<br />
Sand lenses and layers are common with<strong>in</strong> the Clayey foundation. Thus, this part <strong>of</strong> the area was<br />
susceptible to liquefaction under dynamic load<strong>in</strong>g conditions. Consider<strong>in</strong>g the earthquake potential <strong>of</strong><br />
the area (high), the design stage must <strong>in</strong>clude geotechnical <strong>in</strong>vestigations for detailed assessment <strong>of</strong><br />
the foundation conditions (Topal, Doyuran et al. 2003).<br />
In 1997 Noack et.al., published a microzonation study for Basel city <strong>in</strong> Switzerland. The study was<br />
based on detailed knowledge <strong>of</strong> the geological and geotechnical conditions, measurement and <strong>in</strong>terpretation<br />
<strong>of</strong> ambient noise data and numerical modell<strong>in</strong>g <strong>of</strong> expected ground motion. Differ<strong>in</strong>g from the<br />
above-mentioned study they used a detailed rat<strong>in</strong>g scheme us<strong>in</strong>g geographical <strong>in</strong>formation systems,<br />
which accounts for the effects <strong>of</strong> local geological and geotechnical conditions on the amplification <strong>of</strong><br />
ground motion. Seven characteristics parameter were mapped and rated on a 25*25 m grid with<strong>in</strong> the<br />
area <strong>of</strong> the district <strong>of</strong> Basel-Stadt. The result<strong>in</strong>g qualitative microzonation map <strong>of</strong> the center <strong>of</strong> the<br />
town is discussed and compared to the historically reported damage <strong>of</strong> the 1356 earthquake. The result<strong>in</strong>g<br />
map was also a practical tool for recogniz<strong>in</strong>g areas where amplification effects have to be ex-<br />
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pected. It was also envisaged to apply measurements <strong>of</strong> shear-wave velocities, numerical simulations<br />
and calibration to future strong-motion record<strong>in</strong>gs (Noack, 1997)<br />
2.1.3. Ground <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong>; <strong>Soil</strong> <strong>Site</strong> Effects<br />
The nature <strong>of</strong> local site effects can be illustrated <strong>in</strong> many ways by simple theoretical ground response<br />
analyses, by measurements <strong>of</strong> actual surface and subsurface motions at the same site and by measurements<br />
<strong>of</strong> ground surface motions from sites with different subsurface conditions. There are several<br />
techniques, which can be experimental, numerical, advanced, semi-empirical and empirical (Field,<br />
1993 ;Lermo, 1993; Aki, 1991; Schnabel, 1972; ). In general terms, empirical methods use the seismic<br />
records on the local site where the amplification and frequency could be determ<strong>in</strong>ed directly. But on<br />
the other hand the theoretical methods require detailed analysis <strong>of</strong> the geotechnical <strong>in</strong>formation related<br />
to the subsurface <strong>of</strong> the region (Zaslavsky 2001).<br />
Experimental Methods<br />
Experimental methods try to clarify the response on the surface us<strong>in</strong>g the outcomes <strong>of</strong> the seismic records.<br />
The methods use the spectral ratios between the two components (Horizontal and Vertical) <strong>of</strong><br />
the seismic record. The most common used methods are,<br />
• Standard spectral ratio (SSR)<br />
• H/V noise ratio; (Nogishi-Nakamura technique)<br />
• H/V spectral ratio <strong>of</strong> weak motion (HVSR); (Lacave, Bard et al. 2002)<br />
The Standard Spectral Ratio method was widely used through out the world from the year Borcherdt<br />
has <strong>in</strong>troduced it, <strong>in</strong> 1970. Though it is still widely used the latter method proposed by Nakamura <strong>in</strong><br />
1989 (Nakamura 1989) took also big attention. The method <strong>of</strong> Nakamura uses the two components<br />
(horizontal and vertical) <strong>of</strong> background noise at a site and computes the site-specific resonant frequency<br />
from these components. In other words it measures the ratio <strong>of</strong> earthquake shak<strong>in</strong>g at unconsolidated<br />
sedimentary sites with respect to a nearby bedrock reference site. Seismographs are <strong>in</strong>stalled<br />
<strong>in</strong> the field and left to record ambient vibrations. Ambient vibrations can also be called microseisms,<br />
microtremors or ambient noise they refer to cont<strong>in</strong>uous ground motion constitut<strong>in</strong>g background noise<br />
for any seismic experiment. They could <strong>in</strong>volve traffic, mach<strong>in</strong>ery noises and/or seismic tremors. The<br />
method gives the frequency dependent site response amplitude or amplification, relative to the Rock<br />
site (Figure 2-7)<br />
The Standard Spectral Ratio technique uses the comparison <strong>of</strong> the ground surface motions recorded at<br />
several sites <strong>in</strong> the same region. These sites should have the same earthquake source and path effects.<br />
It is assumed that the source, path and site effects on ground motions are separable. Source effect: refers<br />
to the effect <strong>of</strong> the earthquake source on seismic motions. And, path effect: refers to the effect <strong>of</strong><br />
the propagation path on seismic ground motions. From this technique the importance <strong>of</strong> the site effects<br />
also can be observed well. Similar effects have been observed <strong>in</strong> many other earthquakes. Such as<br />
Mexico 1985 earthquake (Stone, Yokel et al. 1987) and the Loma Prieta 1989 (Seed, S.E. et al. 1990)<br />
earthquake. SSR technique uses two conditions: first the reference site should be free <strong>of</strong> any site effect<br />
regard<strong>in</strong>g to the source radiation and travel path mean<strong>in</strong>g, when the reference site is on an unweathered,<br />
horizontal bedrock. Secondly, it should also be close to the exam<strong>in</strong>ed station. Jensen (2000)<br />
24<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
agreed on the method’s functionality but added that it is expensive and cumbersome s<strong>in</strong>ce it requires<br />
an impractical amount <strong>of</strong> time to acquire enough data to zone the area <strong>in</strong> Australia, which is characterized<br />
by <strong>in</strong>frequent earthquakes. The SSR method has also been attempted by record<strong>in</strong>g microtremor<br />
noise, rather than actual earthquakes, simultaneously on hard Rock and sediments and then tak<strong>in</strong>g the<br />
spectral ratio <strong>of</strong> the recorded components. As a conclusion the noise level was so much greater at the<br />
sediment site that the special ratios could not be used to determ<strong>in</strong>e the resonance period for this study.<br />
Another example for the use <strong>of</strong> SSR method is, Triantafyllidis et. al. (1999). They have used the techniques<br />
SSR (Standard Spectral Ratio) and HVSR (H/V spectral ratio <strong>of</strong> weak motion) <strong>in</strong> Thessaloniki<br />
(Greece). The technique <strong>of</strong> SSR was applied to a reference station located on Rock, while the HVSR<br />
technique was applied to earthquake records as well as on noise records. . The results from all methods<br />
were compared <strong>in</strong> terms <strong>of</strong> resonant frequencies and amplification levels. At the end, the obta<strong>in</strong>ed<br />
mean spectral amplifications were compared with those derived from experimental data, the two sets<br />
are found to be consistent at most <strong>of</strong> the stations (Petros Triantafyllidis 1999; Triantafyllidis,<br />
Panagiotis M. Hatzidimitriou et al. 1999).<br />
Second technique; H/V noise ratio was <strong>in</strong>troduced <strong>in</strong> the early seventies by several Japanese scientists<br />
but is <strong>of</strong>ten referred to as the Nogishi-Nakamura technique (Nogoshi and Igarashi 1971;<br />
Nakamura 1989; Y. 1989). This is the ratio between the Fourier spectra <strong>of</strong> the horizontal and vertical<br />
components <strong>of</strong> ambient vibrations. To clarify the Fourier Spectra, these terms should be expla<strong>in</strong>ed.<br />
The seismic records could be accepted as periodic functions. And any periodic function can be expressed<br />
us<strong>in</strong>g the Fourier analysis, which means the sum <strong>of</strong> a series <strong>of</strong> simple harmonic terms <strong>of</strong> different<br />
frequency, amplitude and phase. And, simple harmonic motion can be characterized by s<strong>in</strong>usoidal<br />
motion at constant frequency. Us<strong>in</strong>g the Fourier series a periodic function X (t) can be written as,<br />
∞<br />
X ( t) = c 0 + ∑ c n s<strong>in</strong> (ω n t + φ n )<br />
n = 1<br />
In the formula; c n is the Amplitude and φ n is the phase angle. Fourier amplitude spectrum is plotted<br />
us<strong>in</strong>g the ω n versus c n . For Fourier phase spectrum ω n versus φ n should be plotted.<br />
The technique proposes to use only one record<strong>in</strong>g station <strong>in</strong> the methodology, and assumes that site<br />
response could be estimated from the horizontal (H) to vertical (V) ratio <strong>of</strong> microtremors, also refers to<br />
the name H/V ratio. This technique estimates the site response us<strong>in</strong>g the division between the horizontal<br />
component noise spectra by vertical component noise spectra.<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 25
Figure 2-7 The microtremors are placed to an alluvial site, a Rock site and at the top <strong>of</strong> a hill. The record<strong>in</strong>gs<br />
are received and processed. Then, the amplification spectrum is plotted. The differences between<br />
the sites are expla<strong>in</strong>ed us<strong>in</strong>g the ratios and comparisons <strong>of</strong> the H/V components. This method refers to<br />
Standard Spectral Ratio <strong>of</strong> site effect estimations (Duval, 1994)<br />
Various sets <strong>of</strong> experimental data confirmed that these ratios are much more stable than the raw noise<br />
spectra. Above all, Lacave and Bard added that several theoretical <strong>in</strong>vestigations supported these observations<br />
(Lacave, Bard et al. 2002). They showed that synthetic strong motion records obta<strong>in</strong>ed with<br />
randomly distributed near surface sources lead to horizontal-vertical ratios sharply peaked around the<br />
fundamental S-wave frequency, whenever the surface layers exhibit a sharp difference with the underly<strong>in</strong>g<br />
stiffer formations. Mean<strong>in</strong>g that the formations with high differ<strong>in</strong>g properties; unit weights,<br />
shear wave velocities etc have been estimated successfully from the H/V ratios. On the other hand the<br />
studies formerly mentioned also concluded; the amplitude <strong>of</strong> this peak is not well correlated with the S<br />
wave amplification at the site’s resonant frequency. But more sensitive to Poisson’s ratio near the surface,<br />
which is the ratio <strong>of</strong> the transverse stra<strong>in</strong> to the longitud<strong>in</strong>al extension stra<strong>in</strong> (n). Tensile deformation<br />
(its ability to support a load without break<strong>in</strong>g; the material can be stretch) is considered positive<br />
and compressive deformation is considered negative. The def<strong>in</strong>ition <strong>of</strong> Poisson's ratio conta<strong>in</strong>s a<br />
m<strong>in</strong>us sign so that normal materials have a positive ratio (Figure 2-8).<br />
26<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
n = - e trans / e longitud<strong>in</strong>al<br />
Stra<strong>in</strong> (e) is def<strong>in</strong>ed <strong>in</strong> elementary form as the change <strong>in</strong> length divided by the orig<strong>in</strong>al length. And is<br />
given by the formula;<br />
e = DL/L.<br />
Figure 2-8 Figure show<strong>in</strong>g the representative situation for Poisson’s ratio on material. (Lakes 2004)<br />
In order to apply this technique, one should be aware <strong>of</strong> its limitations <strong>in</strong> different situations. In practice,<br />
the H/V ratios from ambient vibrations are sometimes “non-<strong>in</strong>formative” so that no clear <strong>in</strong>terpretation<br />
is possible. In Figure 2-9, transfer functions are shown which is a mathematical representation<br />
<strong>of</strong> the relation between the <strong>in</strong>put and output <strong>of</strong> a l<strong>in</strong>ear time-fixed system. It is ma<strong>in</strong>ly used <strong>in</strong> signal<br />
process<strong>in</strong>g. The comparison between the graphs show that they provide the fundamental resonant<br />
frequency but fails to give <strong>in</strong>formation on the higher frequencies (Lacave, Bard et al. 2002).<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 27
Figure 2-9 Transfer functions for (a) Standard spectral ratio (e) H/V ratio for S wave part <strong>of</strong> the earthquake<br />
records (f) Nakamura’s technique (H/V ratio <strong>of</strong> ambient vibrations). Dashed l<strong>in</strong>e represent 95%<br />
confidence limits <strong>of</strong> the mean ((Lacave, Bard et al. 2002).<br />
S<strong>in</strong>ce the reliability <strong>of</strong> this technique is under <strong>in</strong>vestigation, there have been several approaches to test<br />
it. One <strong>of</strong> these studies is the project held for European Commission by the Swiss Seismological Service,<br />
Institute <strong>of</strong> Geophysics (Fäh, 2001). The objective <strong>of</strong> the project was to <strong>in</strong>vestigate the reliability<br />
<strong>of</strong> the two techniques developed <strong>in</strong> Japan us<strong>in</strong>g ambient noise record<strong>in</strong>gs; the very simple H/V technique<br />
and the more advanced array technique. The array technique uses the noise record<strong>in</strong>gs on small<br />
aperture arrays. The analysis is thorough spatial correlation to measure the phase velocities <strong>of</strong> surface<br />
waves and <strong>in</strong>vert the surface velocity structure. From this <strong>in</strong>formation then it is possible to compute<br />
the site response theoretically (Fäh, K<strong>in</strong>d et al. 2001). The project is still ongo<strong>in</strong>g but supports the idea<br />
<strong>of</strong> that the technique needs assessment and also has many advantages.<br />
On this topic detailed experimental studies are ongo<strong>in</strong>g but several conclusions appear which shows<br />
that many other observations should be held <strong>in</strong> order to assess the reliability <strong>of</strong> this technique. But<br />
s<strong>in</strong>ce it is one <strong>of</strong> the most <strong>in</strong>expensive methods it is still convenient to estimate fundamental frequencies<br />
<strong>of</strong> s<strong>of</strong>t deposits <strong>in</strong> many cases. Additionally, there are some strong supporters <strong>of</strong> the technique<br />
such as Zaslavsky et al (2001), who had worked on the seismic microzon<strong>in</strong>g <strong>of</strong> Israel us<strong>in</strong>g the Nakamura<br />
technique, where they focused on 3 steps:<br />
• Detailed mapp<strong>in</strong>g <strong>of</strong> site response functions us<strong>in</strong>g microtremor record<strong>in</strong>gs<br />
• Use <strong>of</strong> geological <strong>in</strong>formation and borehole data with empirically obta<strong>in</strong>ed response functions<br />
to derive subsurface models for different sites across the study area<br />
• Estimat<strong>in</strong>g the seismic hazard <strong>in</strong> terms <strong>of</strong> uniform hazard site specific acceleration Spectra.<br />
Another support<strong>in</strong>g example is that from Louie et al (2003) from the Seismological Laboratory <strong>of</strong> University<br />
Nevada, who tried to compare the microtremor refraction and borehole logg<strong>in</strong>g refraction<br />
methods. They have obta<strong>in</strong>ed similar average velocities and spectra between the velocity models estimated<br />
with refraction methods and borehole logg<strong>in</strong>g. But also concluded that the add<strong>in</strong>g <strong>of</strong> geological<br />
<strong>in</strong>formation to models suggests velocities from only the upper 100 meters are not adequate for estimat<strong>in</strong>g<br />
spectra (Louie, R. et al. 2003).<br />
The third technique; H/V spectral ratio (HVSR) <strong>of</strong> weak motion is another simple technique that<br />
consists <strong>in</strong> tak<strong>in</strong>g the spectral ratio between the horizontal and the vertical components <strong>of</strong> the shear<br />
wave part <strong>of</strong> weak earthquake record<strong>in</strong>gs. Lermo and Chavez-Garcia (Lermo and Chavez-Garcia<br />
1993) applied the method <strong>in</strong> Mexico. These record<strong>in</strong>gs exhibit very encourag<strong>in</strong>g similarities between<br />
the classical spectral ratios and these HVSR, with good fit <strong>in</strong> both, the frequencies and amplitudes <strong>of</strong><br />
the fundamental resonant peaks.<br />
28<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
Several other studies have looked to this technique and end up with good results, such as the HVSR<br />
shape showed good experimental stability, also well correlation with surface geology. But also, the<br />
absolute level <strong>of</strong> HVSR depends on the type <strong>of</strong> <strong>in</strong>cident waves. Incident wave term is used <strong>in</strong> Snell’s<br />
law that refers to the waves refraction and reflection <strong>in</strong> optics. Optics properties could also be used<br />
when the seismic wave passes between two media. The formula given is represents the relation between<br />
the waves; the normal one and the reflected or refracted one.<br />
Figure 2-10 The <strong>in</strong>cident wave and its reflected and refracted components <strong>in</strong> two media. (Transverse<br />
waves are S-waves and longitud<strong>in</strong>al waves are the P-waves).<br />
The angles α and β <strong>in</strong> the figure are used <strong>in</strong> the formula. The theory assumes that the seismic wave<br />
comes to the boundary <strong>of</strong> the two different mediums and changes its direction with different angles<br />
and this can be related to its speed given <strong>in</strong> the formula. Furthermore it should be po<strong>in</strong>ted out that this<br />
technique has been applied and checked for s<strong>of</strong>t soil sites only and might not be valid for other k<strong>in</strong>ds<br />
<strong>of</strong> site effects (Lacave, Bard et al. 2002).<br />
The experimental methods expla<strong>in</strong>ed <strong>in</strong> short summaries <strong>in</strong> this section provide important <strong>in</strong>formation<br />
for the fundamental resonance frequency on the site. The peak amplification factor decreases with the<br />
natural frequency <strong>of</strong> soils, the greatest amplification factor will occur approximately at the lowest<br />
natural frequency which is also known as the fundamental frequency and is given by (Kramer, 1996);<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 29
ω n ≅ Vs / H ( π /2 + n π)<br />
In general, several record<strong>in</strong>g stations are needed to pick up the ambient noises near the study area (except<br />
Nakamura) and if possible microtremors; real earthquake record<strong>in</strong>gs are needed for these analysis.<br />
These studies would be appropriate where the record<strong>in</strong>gs or the <strong>in</strong>struments for record<strong>in</strong>g the signals<br />
are available. In case <strong>of</strong> this research, time, budget and data constra<strong>in</strong>ts did not allow to implement<br />
these experimental studies <strong>in</strong> the site. But, these <strong>in</strong>vestigations would be appropriate for future s<strong>in</strong>ce<br />
they would provide double-check for the shear wave velocities and the fundamental resonance frequency.<br />
As, the two parameters are very related to the build<strong>in</strong>g codes, the results will improve the accuracy<br />
<strong>of</strong> the build<strong>in</strong>g codes be<strong>in</strong>g used for that time.<br />
Numerical <strong>Analysis</strong><br />
If the geotechnical characteristics <strong>of</strong> a site are known then, the site effects can be estimated us<strong>in</strong>g numerical<br />
analysis. Sufficient density <strong>of</strong> boreholes and sufficient geotechnical <strong>in</strong>formation will allow the<br />
application <strong>of</strong> numerical analysis for numerically based zon<strong>in</strong>g. The numerical methods <strong>of</strong> site effects<br />
could be dist<strong>in</strong>guished as follows,<br />
• One dimensional response <strong>of</strong> soil columns<br />
• Advanced methods<br />
S<strong>in</strong>ce the one-dimensional response <strong>of</strong> soil columns is the ma<strong>in</strong> method used <strong>in</strong> this research it will be<br />
treated <strong>in</strong> more detail. Here the new approaches and arguments accord<strong>in</strong>g the literature will be discussed.<br />
For one-dimensional response analysis the soil and bedrock surface are assumed to be extend<strong>in</strong>g horizontally<br />
and <strong>in</strong>f<strong>in</strong>itely. The method simply uses, the geotechnical parameters <strong>of</strong> soils <strong>in</strong> l<strong>in</strong>ear or nonl<strong>in</strong>ear<br />
behaviour us<strong>in</strong>g specific calculations to estimate the ground response for a specific <strong>in</strong>put motion.<br />
In l<strong>in</strong>ear systems the structure damage is proportional to the ground shak<strong>in</strong>g, which means the<br />
level <strong>of</strong> shak<strong>in</strong>g assigns the level <strong>of</strong> damage. On the other hand, non-l<strong>in</strong>ear systems behave different at<br />
each level <strong>of</strong> shak<strong>in</strong>g. The reason <strong>of</strong> the damage results from the changes <strong>in</strong> the structure while the<br />
shak<strong>in</strong>g <strong>in</strong>creases. In l<strong>in</strong>ear approaches the nonl<strong>in</strong>earity could also be implemented us<strong>in</strong>g the soils<br />
properties such as damp<strong>in</strong>g and rigidity. With this k<strong>in</strong>d <strong>of</strong> calculations the <strong>in</strong>put parameters are based<br />
on velocity <strong>of</strong> shear wave, unit weight, thickness and damp<strong>in</strong>g. These parameters could be obta<strong>in</strong>ed<br />
us<strong>in</strong>g direct <strong>in</strong> situ measurements or from drill<strong>in</strong>gs and subsequent laboratory measurements or from<br />
known relations between the parameters such as us<strong>in</strong>g SPT-N (Standard Penetration Test, N values)<br />
values for the shear moduli calculation. Shake2000 s<strong>of</strong>tware is one <strong>of</strong> the most common programs that<br />
are used for these calculations (see chapter 3).<br />
And for the non-l<strong>in</strong>ear models CyberQuake program can be used (CyberQuake 1998). However, this<br />
analysis requires a quantitative knowledge <strong>of</strong> actual non-l<strong>in</strong>ear material behaviour, which can be obta<strong>in</strong>ed<br />
by sophisticated laboratory tests. As can be concluded, the approach requires deep understand<strong>in</strong>g<br />
<strong>of</strong> analytical models and the numerical methods. If the approach is not handled with care, the result<br />
could be unreliable <strong>in</strong> both cases l<strong>in</strong>ear or non-l<strong>in</strong>ear.<br />
In one dimensional ground response analysis, the l<strong>in</strong>ear and non-l<strong>in</strong>ear approaches are compared <strong>in</strong><br />
literature. Although equivalent l<strong>in</strong>ear approach provides reasonable results for many practical problems<br />
and is widely used, it rema<strong>in</strong>s an approximation <strong>of</strong> the reality. Here, the mathematical aspects <strong>of</strong><br />
30<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
the two approaches are not go<strong>in</strong>g to be presented but some <strong>of</strong> the terms could be expla<strong>in</strong>ed related to<br />
the approaches. An alternative approach is to analyse the actual non-l<strong>in</strong>ear response <strong>of</strong> a soil deposit<br />
us<strong>in</strong>g direct numerical <strong>in</strong>tegration <strong>in</strong> the time doma<strong>in</strong>, which falls under the non-l<strong>in</strong>ear approach title.<br />
In l<strong>in</strong>ear approach transfer functions are used to compute the response <strong>of</strong> s<strong>in</strong>gle degree <strong>of</strong> freedom systems.<br />
Simply, mentioned before a transfer function is a function that relates one parameter to another.<br />
And s<strong>in</strong>gle degree <strong>of</strong> freedom system is a discrete system whose position can be described completely<br />
by a s<strong>in</strong>gle variable (Figure 2-3).<br />
The mathematical analyses <strong>of</strong> the two approaches differ so the results obta<strong>in</strong>ed also differ. There has<br />
been some results obta<strong>in</strong>ed on the comparison <strong>of</strong> the approaches (Joyner and Chen 1975; Mart<strong>in</strong> and<br />
Seed 1978; Dikmen and Ghaboussi 1984).<br />
In general the results can be listed as follows;<br />
1. Artificial high amplifications may occur due to a strong component <strong>of</strong> the <strong>in</strong>put motion that<br />
corresponds with the natural frequency <strong>of</strong> a l<strong>in</strong>ear soil deposit.<br />
2. The use <strong>of</strong> an effective shear stra<strong>in</strong> <strong>in</strong> an equivalent l<strong>in</strong>ear analysis can lead to an over s<strong>of</strong>tened<br />
and over-damped system.<br />
3. Equivalent l<strong>in</strong>ear analyses can be much more efficient than non-l<strong>in</strong>ear analyses.<br />
4. Non-l<strong>in</strong>ear methods can be formulated <strong>in</strong> terms <strong>of</strong> effective stresses to allow modell<strong>in</strong>g <strong>of</strong> the<br />
generation, redistribution and eventual dissipation <strong>of</strong> excess pore pressure dur<strong>in</strong>g and after<br />
earthquake shak<strong>in</strong>g. Equivalent l<strong>in</strong>ear methods do not have this capability.<br />
5. Non-l<strong>in</strong>ear methods require a reliable stress-stra<strong>in</strong> or constitutive model.<br />
6. Differences between the results <strong>of</strong> equivalent l<strong>in</strong>ear and non-l<strong>in</strong>ear analyses depend on the degree<br />
<strong>of</strong> nonl<strong>in</strong>earity <strong>in</strong> the actual soil response.<br />
In conclusion both <strong>of</strong> the approaches could be used successfully for one dimensional ground response<br />
analysis. Neither can be considered mathematically exact or precise, yet their accuracy is not consistent<br />
with the variability <strong>in</strong> soil conditions, uncerta<strong>in</strong>ty <strong>in</strong> soil properties and scatter <strong>in</strong> the experimental<br />
data upon which many <strong>of</strong> their <strong>in</strong>put parameters are based (Kramer 1996). The dependency to the <strong>in</strong>put<br />
parameters and their variability highlights this study’s importance. It is very essential that we<br />
know about the parameters variability as mentioned <strong>in</strong> the previous paragraph. Many analysis are held<br />
depend<strong>in</strong>g on many assumptions, where at some levels this will lead to less accurate outcomes.<br />
After discuss<strong>in</strong>g the two approaches, one <strong>of</strong> the examples that use the non-l<strong>in</strong>ear approach is done by<br />
Slob and Hack (2002). They had suggested us<strong>in</strong>g the GIS and SHAKE comb<strong>in</strong>ed <strong>in</strong> an iterative way<br />
for microzonation for Armenia, Colombia. They have proposed us<strong>in</strong>g an automat<strong>in</strong>g the repetition <strong>of</strong><br />
response calculation through the execution <strong>of</strong> a computer program that forms the <strong>in</strong>terface between the<br />
gridded semi-3D ground model from the GIS and the seismic response calculation program SHAKE.<br />
Also, they used the geological conditions after the classification <strong>in</strong>to areas <strong>of</strong> different hazard level is<br />
done, contradictory to the traditional way, which generally uses the geological conditions at first hand.<br />
Conclusively the case study area showed correlation between the spatial variations <strong>of</strong> the spectral acceleration<br />
for different frequencies and the observations after the earthquake happened (Slob, Hack et<br />
al. 2002).<br />
Another study that used SHAKE (91) and one-dimensional ground response was done by Rodriguez-<br />
Marek and Bray (1999), they have used this s<strong>of</strong>tware and analysis <strong>in</strong> order to understand the behaviour<br />
<strong>of</strong> soil deposits. They have suggested a methodology for development <strong>of</strong> the proposed empirically<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 31
ased site-dependent amplification factors. For the classification scheme <strong>of</strong> the site, they have used<br />
SHAKE91 and checked the responses. And, observed that an <strong>in</strong>crease <strong>in</strong> depth shifts the fundamental<br />
period, where amplification is most significant, toward higher values. Also added that, the significantly<br />
higher response at longer periods for deep soil deposits is an important expected result that<br />
should be accommodated <strong>in</strong> a seismic site response evaluation (Rodriguez-Marek and and Bray 1999).<br />
Overall, it can be concluded that one dimensional soil column analysis is a practical method and<br />
widely used <strong>in</strong> many studies and the applications have varieties <strong>in</strong> soil site effect analysis.<br />
Advanced methods<br />
Advanced methods refer to the different models that have been proposed to <strong>in</strong>vestigate several <strong>of</strong> the<br />
various aspects <strong>of</strong> site effects. These aspects usually <strong>in</strong>volve complex phenomena. Various types <strong>of</strong><br />
<strong>in</strong>cident wave fields, such as near field (comparable or shorter than the wavelength concerned.), far<br />
field (It is used to refer a distance to a seismic source longer than the wavelength concerned), body<br />
waves, surface waves should be considered. The structure geometry may be 1D, 2D or 3D (Figure 2-<br />
11). Or, the mechanical behaviour <strong>of</strong> materials may have a very wide range like, viscoelasticity (Viscoelastic<br />
materials are those for which the relationship between stress and stra<strong>in</strong> depends on time),<br />
non-l<strong>in</strong>ear behaviour, water-saturated media and liquid doma<strong>in</strong>s.<br />
Figure 2-11 Subsurface geology could be referred as one-dimensional, two-dimensional or threedimensional<br />
(Smith 2001).<br />
Lacave et. al (2002) have dist<strong>in</strong>guished these complex conditions <strong>in</strong>to four.<br />
1. Analytical methods<br />
2. Ray methods<br />
3. Boundary based techniques<br />
4. Doma<strong>in</strong> based techniques<br />
Above mentioned methods need heavy computational processes, on the other hand their flexibility and<br />
versatility have leaded the way to the understand<strong>in</strong>g <strong>of</strong> the site effects.<br />
In one-dimensional response analysis the soil structure is essentially horizontal. However the conditions<br />
<strong>of</strong> other structures should also be taken <strong>in</strong>to account. Slop<strong>in</strong>g or irregular ground surfaces, the<br />
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presence <strong>of</strong> heavy structures or stiff, embedded structures or walls or tunnels all require twodimensional<br />
even three-dimensional analysis. For this k<strong>in</strong>d <strong>of</strong> problem analysis, the common approach<br />
is to make the analysis us<strong>in</strong>g dynamic f<strong>in</strong>ite-elements (This method assumes that a cont<strong>in</strong>uum as an<br />
composition <strong>of</strong> discrete elements whose boundaries are def<strong>in</strong>ed by nodal po<strong>in</strong>ts, and uses the response<br />
<strong>of</strong> the cont<strong>in</strong>uum can be described by the response <strong>of</strong> the nodal po<strong>in</strong>ts; Figure 2-12) An example for a<br />
required three-dimensional analysis could be an earth dam <strong>in</strong> a narrow canyon, a site where the subsurface<br />
geology differs too much <strong>in</strong> 3D or a site where the soil response is <strong>in</strong>fluenced by response <strong>of</strong><br />
other structures (Kramer 1996).<br />
Figure 2-12 Diagram show<strong>in</strong>g the cont<strong>in</strong>uum and the nodal po<strong>in</strong>ts (Kramer, 1996)<br />
Konno et. al. (1999) tested the analytical methods used for California us<strong>in</strong>g empirical modell<strong>in</strong>g. They<br />
have used two dense 3D strong motion arrays and operated <strong>in</strong> California to directly measure the response<br />
<strong>of</strong> stiff quaternary soil to earthquake shak<strong>in</strong>g. They have recommended that the site response<br />
measurements from these arrays along with detailed geotechnical and geophysical site <strong>in</strong>vestigations<br />
would provide important calibration and confirmation <strong>of</strong> site response modell<strong>in</strong>g techniques used for<br />
seismic sit<strong>in</strong>g criteria development (Konno, Kato et al. 1999).<br />
Lacave et. al. (2002) have po<strong>in</strong>ted out some <strong>of</strong> the concerns related to site effects evaluations. They<br />
have highlighted that the numerical models were a posterior computation, basically the analyser knew<br />
what to look and f<strong>in</strong>d. They have also found the compil<strong>in</strong>g the sufficient <strong>in</strong>put parameters, which depend<br />
on geotechnical and geophysical <strong>in</strong>vestigations to be expensive. Add<strong>in</strong>g, “This issue may sometimes<br />
be overcome through parametric studies, but this is useful only when the results do not exhibit<br />
too much sensitivity (which is rarely the case)”. Here we can see that they have already proposed to<br />
overcome the situation by parametric studies such as this one. But they also argued the sensitiveness<br />
<strong>of</strong> the results. The result <strong>of</strong> this research might give some answers to this op<strong>in</strong>ion.<br />
Empirical and semi-empirical methods<br />
<strong>Seismic</strong> waves <strong>of</strong> all types are progressively damped as they travel because <strong>of</strong> the <strong>in</strong>elastic properties<br />
(stiffness etc) <strong>of</strong> the Rocks and soils (Bolt 2001). The amplitude <strong>of</strong> seismic waves changes for two<br />
ma<strong>in</strong> reasons; first, the wave front usually spreads out as it travels away from the source and, because<br />
the energy <strong>in</strong> it has to be shared over a greater area, the amplitude decreases. Second, it happens when<br />
some <strong>of</strong> the wave energy is absorbed (Musset and Khan 2000). Many empirical attenuation laws have<br />
been derived on the basis <strong>of</strong> available strong ground motion record<strong>in</strong>gs. They all relate to the magnitude,<br />
distance and ground motion parameter; they also might consider the site parameter <strong>in</strong> a simple<br />
manner such as Rock or non-Rock. The reason for this is detailed <strong>in</strong>formation on strong ground motion<br />
record<strong>in</strong>g sites are generally miss<strong>in</strong>g. But a very important development <strong>in</strong> this area has been <strong>in</strong><br />
Japan. They have <strong>in</strong>stalled 1000 sites with 20 m deep boreholes for obta<strong>in</strong><strong>in</strong>g P and S waves after the<br />
destructive earthquake Kobe. The network is called K-Net. (K-Net 2002)<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 33
Another type <strong>of</strong> empirical methods uses Green’s function, which orig<strong>in</strong>ally comes from seismology<br />
studies. In seismology, Green’s functions are mathematical representations <strong>of</strong> how the earth’s geologic<br />
structure affects seismic waves generated by small earthquakes (Figure 2-13). Artificial ground motions<br />
can be developed <strong>in</strong> a number <strong>of</strong> different ways. And generation <strong>of</strong> artificial motions us<strong>in</strong>g<br />
Green’s functions is one <strong>of</strong> them. S<strong>in</strong>ce the subsurface geology is <strong>in</strong> most cases not well known,<br />
though the aim is to figure out it <strong>in</strong> detail us<strong>in</strong>g these functions one should choose a simple geology<br />
structure. Green’s functions are similar to actual record<strong>in</strong>gs <strong>of</strong> micro earthquakes. As such, these record<strong>in</strong>gs<br />
can be used <strong>in</strong>stead <strong>of</strong> mathematical forms to more accurately represent the seismic waves<br />
that could be expected at any given po<strong>in</strong>t on or <strong>in</strong> the earth, even when we don’t know the subsurface<br />
structure. The significant differentiation from the general methods which only look at parameters obta<strong>in</strong>ed<br />
at a s<strong>in</strong>gle moment <strong>in</strong> time, is that it <strong>in</strong>corporates the whole time history, rather than simply at<br />
one po<strong>in</strong>t <strong>in</strong> time (Hutch<strong>in</strong>gs 1999).<br />
Figure 2-13 The diagram for the Empirical Green’s function method (Bour 1994)<br />
The Empirical Green’s Function method also has two types <strong>of</strong> approaches <strong>in</strong> literature. The basic difference<br />
between the two is summ<strong>in</strong>g up <strong>of</strong> the EGF. First one sums up with k<strong>in</strong>ematic models (Irikura<br />
1983; Irikura 1986; Hutch<strong>in</strong>gs 1994; Irikura and K. Kamae 1994) . The second approach uses essentially<br />
statistical tools that allow to sum up the EGF’s <strong>in</strong> a way that the relevant earthquake scal<strong>in</strong>g laws<br />
will be presented (Lacave, Bard et al. 2002).<br />
2.1.4. <strong>Sensitivity</strong> <strong>Analysis</strong><br />
One <strong>of</strong> the ma<strong>in</strong> objectives for this research is to assess the sensitivity <strong>of</strong> the parameters that can be<br />
used to determ<strong>in</strong>e a microzonation study <strong>in</strong> Kathmandu Valley, Lalitpur. In simple words, sensitivity<br />
analysis measures the impact on analysis outcomes <strong>of</strong> chang<strong>in</strong>g one or more key <strong>in</strong>put values about<br />
which there is uncerta<strong>in</strong>ty. Pr<strong>in</strong>cipally, a pessimistic, expected and optimistic value could be chosen to<br />
be the uncerta<strong>in</strong> variables. Then, an analysis could be performed with each variable at a time while the<br />
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other parameters are kept constant. As a result, the outcomes would be <strong>in</strong>terpreted related to the chosen<br />
values.<br />
All <strong>in</strong>direct <strong>in</strong>ference <strong>of</strong> parameters and system states <strong>in</strong> the Earth Sciences is subject to uncerta<strong>in</strong>ty<br />
(Symes, Stark et al. 2002). Uncerta<strong>in</strong>ty is associated with <strong>in</strong>complete or imperfect knowledge and <strong>in</strong>herent<br />
to a physical process or property (Steward 2002).<br />
The complexity <strong>of</strong> the Earth system imposes limitations: many features <strong>of</strong> the subsurface have an aggregate<br />
effect on the data and estimation <strong>of</strong> these subresolution aspects <strong>of</strong> models is subject to great<br />
ambiguity. Many approaches have been proposed to quantify this uncerta<strong>in</strong>ty, <strong>in</strong>clud<strong>in</strong>g l<strong>in</strong>ear sensitivity<br />
analysis, Bayesian PDF estimation, m<strong>in</strong>imax, construction <strong>of</strong> solutions that are extreme <strong>in</strong> some<br />
sense and many others. Such studies are meant to provoke much needed progress towards better understand<strong>in</strong>g<br />
<strong>of</strong> the <strong>in</strong>formation content <strong>of</strong> geophysical data (Symes, Stark et al. 2002) .<br />
Above all, the sensitivity and uncerta<strong>in</strong>ty analyses should address parameter selection and ranges, not<br />
the selection <strong>of</strong> scenarios. On the other hand this research’s aim is also to touch on the scenarios created<br />
us<strong>in</strong>g the <strong>in</strong>put motion and parameters <strong>in</strong> Shake2000. Because the case study done <strong>in</strong> this research<br />
can also be analysed us<strong>in</strong>g the values sensitivity. The results could also address the scenario or methodology’s<br />
quality, which is used for the site. In site response the uncerta<strong>in</strong>ty could be found <strong>in</strong> the<br />
non-l<strong>in</strong>ear properties <strong>of</strong> velocity <strong>of</strong> shear wave <strong>in</strong> spatial varieties and measurement errors and for<br />
shear modulus and depth parameters <strong>in</strong> non-l<strong>in</strong>ear properties and sample disturbance. To deal with<br />
such problems one can use the conventional sensitivity/uncerta<strong>in</strong>ty analysis methods.<br />
Conventional methods for sensitivity and uncerta<strong>in</strong>ty propagation can be broadly classified <strong>in</strong>to four<br />
categories (Isukapalli 1999). Form the list; “<strong>Sensitivity</strong> Test<strong>in</strong>g” is applied <strong>in</strong> this study.<br />
• <strong>Sensitivity</strong> test<strong>in</strong>g<br />
• Analytical methods<br />
• Sampl<strong>in</strong>g based methods<br />
• Computer algebra methods<br />
The general methodology is to figure out the important parameters <strong>in</strong> a model, mak<strong>in</strong>g multiple runs<br />
for specific values chosen and fitt<strong>in</strong>g a polynomial least square analysis to the result curve. This fitted<br />
response surface is then used as a replacement or proxy for the computer model and all <strong>in</strong>ferences related<br />
to sensitivity/uncerta<strong>in</strong>ty analysis for the orig<strong>in</strong>al model are derived from this fitted model.<br />
Regard<strong>in</strong>g to the sensitivity analysis and Shake2000 s<strong>of</strong>tware, there were no literature reachable at the<br />
moment. But there are some other analysis done which are related to the approach and here will be<br />
summarized.<br />
Helton, (Helton 1993) studied the applicability <strong>of</strong> response surface methods <strong>in</strong> performance assessment<br />
<strong>of</strong> radioactive waste disposal. It has also been used <strong>in</strong> conjunction with soil erosion modell<strong>in</strong>g,<br />
with vegetative plant growth modell<strong>in</strong>g and with structural reliability problems. Rebez and Slejko did<br />
an example <strong>of</strong> sensitivity analysis on the seismic hazard estimates for Italy <strong>in</strong> 2000. They have chosen<br />
the parameters to be important. Add<strong>in</strong>g that, these choices are subjective and undoubtedly condition<br />
the f<strong>in</strong>al results. The choices were;<br />
• The def<strong>in</strong>ition <strong>of</strong> maximum magnitudes for the seismogenic zones<br />
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• The def<strong>in</strong>ition <strong>of</strong> variable s<strong>of</strong>t boundaries <strong>of</strong> the seismogenic zones<br />
• The choice <strong>of</strong> the seismicity rates as an <strong>in</strong>put<br />
• The PGA attenuation relation chosen.<br />
The scope <strong>of</strong> this work was to analyse the sensitivity <strong>of</strong> the hazard estimates when different choices<br />
are considered for the above-mentioned <strong>in</strong>put parameters. These data were used to perform several<br />
tests. The conclusions were; the major differences were caused by the <strong>in</strong>troduction <strong>of</strong> s<strong>of</strong>t boundaries<br />
for the seismogenic zones and by the cautious corrections <strong>of</strong> the seismicity rates com<strong>in</strong>g from the<br />
completeness analysis. Secondly, the <strong>in</strong>fluence <strong>of</strong> the attenuation relation seems relevant only <strong>in</strong> specific<br />
areas such as southern Italy, where high magnitude earthquakes with a very long return period<br />
occur (Rebez and Slejko 2000).<br />
There are other studies, which focuses on the <strong>in</strong>put parameter assessments for seismic hazard. In Switzerland,<br />
(Sellami, F. Bay et al.) have been assess<strong>in</strong>g the <strong>in</strong>put parameter selection and ranges. The outcome<br />
<strong>of</strong> this study will also address the estimation <strong>of</strong> uncerta<strong>in</strong>ties for the region. In site effects <strong>in</strong>put<br />
parameters assessments <strong>of</strong> Rodriguez-Marek and Bray (1999) they have found that both analytical<br />
studies and observation <strong>of</strong> previous earthquakes <strong>in</strong>dicated depth is <strong>in</strong>deed an important parameter<br />
affect<strong>in</strong>g seismic site response (Rodriguez-Marek and and Bray 1999) <strong>Sensitivity</strong> studies (Field and<br />
Jacob 1993) also draw attention to the need for multiple redundant geotechnical measurements (which<br />
<strong>in</strong>creases the actual cost <strong>of</strong> numerical estimations) (Lacave, Bard et al. 2002).<br />
2.2. Conclusıons<br />
This literature review was done <strong>in</strong> the early stages <strong>of</strong> the study, the list <strong>of</strong> reference has been<br />
broadened while the study cont<strong>in</strong>ued. The concept <strong>of</strong> seismic hazard assessment, microzonation and<br />
ground response analysis is very wide and has been on the focus <strong>of</strong> scientific community for long<br />
years. The aim for this review was to br<strong>in</strong>g the latest ones as possible. More detailed research can be<br />
and should be done <strong>in</strong> order to have a better review <strong>in</strong> all the topics. One <strong>of</strong> the difficulties faced was<br />
the absence <strong>of</strong> sensitivity analysis as it is and the sensitivity analysis done for the response analysis.<br />
There were not sufficient works done or reached for the help <strong>of</strong> this study <strong>in</strong> the response analysis. On<br />
the other hand the review supported the approach that is used for this study. For example, the<br />
experimental methods were not proper enough to apply <strong>in</strong> the chosen study area, because <strong>of</strong> the time,<br />
budget and data constra<strong>in</strong>ts. The second option which is the numerical analysis was not really proper<br />
s<strong>in</strong>ce the geotechnical parameters were not known very well <strong>in</strong> the site. Though, many boreholes were<br />
obta<strong>in</strong>ed for the Kathmandu Valley, from this database only 14 boreholes (even 10 s<strong>in</strong>ce 4 <strong>of</strong> them are<br />
very close po<strong>in</strong>ts to each other) were <strong>in</strong> Lalitpur. And from this list only 2 <strong>of</strong> them had a couple <strong>of</strong><br />
geotechnical <strong>in</strong>formation needed. So this was also not applicable. That is also another reason why the<br />
focus was moved to sensitivity analysis. But the ma<strong>in</strong> reason here is to try solv<strong>in</strong>g the data lack<strong>in</strong>g<br />
problem us<strong>in</strong>g some statistical analysis and compare them with simplified reality.<br />
This review also helped for future studies that could be related to this one. For <strong>in</strong>stance, the advanced<br />
methods <strong>in</strong> numerical analysis and the comb<strong>in</strong>ation <strong>of</strong> the empirical and numerical methods could also<br />
highlight new approaches to deal with the data lack<strong>in</strong>g problem. And it is also possible to use the other<br />
statistical methods mentioned (analytical methods, sampl<strong>in</strong>g based methods and computer algebra<br />
methods) <strong>in</strong> order to understand better the behaviour and range <strong>of</strong> values for the <strong>in</strong>put parameters.<br />
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3. Shake2000<br />
3.1. Introduction<br />
Local site effects <strong>in</strong>fluence the <strong>in</strong>tensity <strong>of</strong> shak<strong>in</strong>g, and they have been a popular research area for<br />
many earthquake eng<strong>in</strong>eers, seismologists and other scientists. The reason is also it plays an important<br />
role <strong>in</strong> earthquake resistant design <strong>of</strong> build<strong>in</strong>gs. The basics <strong>of</strong> this analysis depend on the wave propagation<br />
theory. In a nutshell the theory comes from seismology, which studies the ability <strong>of</strong> seismic<br />
waves -vibrations <strong>of</strong> Rocks- to propagate through the Earth. Generally, seismic waves do not travel <strong>in</strong><br />
straight l<strong>in</strong>es but are deflected, by refraction or reflection, by the layers they encounter, before they<br />
return to the surface <strong>of</strong> the Earth and this allows the <strong>in</strong>ternal structure to be determ<strong>in</strong>ed (Musset and<br />
Khan 2000).<br />
Us<strong>in</strong>g wave propagation theory comb<strong>in</strong>ed with material properties and seismic <strong>in</strong>put motion the expected<br />
ground movement could be determ<strong>in</strong>ed. This is done us<strong>in</strong>g quantitative <strong>in</strong>puts <strong>in</strong>to complex<br />
mathematical calculations. One <strong>of</strong> the earliest and most successful attempts was <strong>in</strong> the early seventies<br />
when Schabel and Lysmer (1972) published, “A computer program for conduct<strong>in</strong>g equivalent l<strong>in</strong>ear<br />
seismic response analyses for horizontally layered soil deposits” called SHAKE. This s<strong>of</strong>tware was<br />
based on Kanai (1951), Roesset and Whitman (1969), and Tsai and Housner (1970), SHAKE assumes<br />
that the recurrent and circular soil behaviour can be simulated us<strong>in</strong>g an equivalent l<strong>in</strong>ear model (e.g.<br />
(Kramer 1996)). From then, many upgrades and derived programs have been released. In general the<br />
upgrades were focused on the user friendl<strong>in</strong>ess <strong>of</strong> the s<strong>of</strong>tware; the fundamental part; the core algorithm<br />
was left untouched. The program is still <strong>in</strong> use widely all over the world and the upgrades are<br />
still cont<strong>in</strong>u<strong>in</strong>g <strong>in</strong> the same way.<br />
3.2. Background<br />
The s<strong>of</strong>tware that is used <strong>in</strong> this research is called SHAKE2000, which is a s<strong>of</strong>tware package that <strong>in</strong>tegrates<br />
ShakEdit and SHAKE. Computer programs such as WESHAKE (Wallace, 1999), ProShake<br />
(Edu Pro Civil Systems, 2002) and ShakEdit are examples <strong>of</strong> the trend towards the development <strong>of</strong><br />
the next generation <strong>of</strong> user-friendly, geotechnical earthquake eng<strong>in</strong>eer<strong>in</strong>g s<strong>of</strong>tware. ProShake, was<br />
developed from EduShake, is a public doma<strong>in</strong> program developed to help eng<strong>in</strong>eer<strong>in</strong>g students understand<br />
the mechanics <strong>of</strong> seismic ground response. Differ<strong>in</strong>g from the ProShake, EduShake can only be<br />
used with the seven ground motions that are <strong>in</strong>cluded <strong>in</strong> the s<strong>of</strong>tware itself. The development <strong>of</strong><br />
EduShake evolved through several stages and was eventually beta tested by graduate students, researchers<br />
and practic<strong>in</strong>g eng<strong>in</strong>eers. After a few modifications <strong>in</strong> response to the comments <strong>of</strong> beta testers,<br />
EduShake was made public doma<strong>in</strong>. Shortly thereafter, the restrictions <strong>of</strong> EduShake were removed<br />
and a few additional features added to produce ProShake. And, ProShake featured a w<strong>in</strong>dows<br />
graphical user <strong>in</strong>terface that both simplifies and speeds the analysis and <strong>in</strong>terpretation <strong>of</strong> seismic<br />
ground response (Edu Pro Civil Systems, 2002 ).<br />
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In addition to the above-mentioned s<strong>of</strong>tware, <strong>in</strong> 1998, the computer program EERA was developed<br />
start<strong>in</strong>g from the same basic concepts as SHAKE. EERA stands for “Equivalent l<strong>in</strong>ear Earthquake <strong>Response</strong><br />
<strong>Analysis</strong>”. EERA implements the well-known concepts <strong>of</strong> equivalent l<strong>in</strong>ear earthquake site<br />
response analysis tak<strong>in</strong>g advantages <strong>of</strong> FORTRAN 90 and spreadsheet program Excel. In 2001, the<br />
implementation pr<strong>in</strong>ciples used for EERA were applied to NERA, a nonl<strong>in</strong>ear site response analysis<br />
program based on the material model developed by Iwan (1967) and Mroz (1967). NERA stands for<br />
“Non-l<strong>in</strong>ear Earthquake <strong>Response</strong> <strong>Analysis</strong>” and takes full advantages <strong>of</strong> FORTRAN90 and Excel.<br />
Concepts similar to those <strong>in</strong> NERA have been used by Joyner and Chen (1975) and Lee and F<strong>in</strong>n<br />
(1978). The French Geology Survey BRGM developed another s<strong>of</strong>tware called CyberQuake, <strong>in</strong> 1998.<br />
The s<strong>of</strong>tware was meant for Earthquake eng<strong>in</strong>eers and researchers. It uses the 1D geometry; multi layered<br />
soil pr<strong>of</strong>iles with no lateral heterogeneity. Differ<strong>in</strong>g from the other s<strong>of</strong>tware it has the choices like<br />
rigid or deformable Rock, totally dra<strong>in</strong>ed condition for layers above the water level and totally or partially<br />
dra<strong>in</strong>ed conditions for saturated layers underneath the water level.<br />
The future developments <strong>in</strong> ground response analysis s<strong>of</strong>tware seems to be improv<strong>in</strong>g the abilities <strong>of</strong><br />
<strong>in</strong>put and output <strong>of</strong> the basic theory and mak<strong>in</strong>g it more user friendly. One <strong>of</strong> the recent developments<br />
regard<strong>in</strong>g to this issue is that the Shake maps are produced onl<strong>in</strong>e on the <strong>in</strong>ternet (Wald, 1999). Follow<strong>in</strong>g<br />
moderate and large earthquakes, this rapid -response ground motions maps are generated<br />
automatically (Figure 3-1). So there is a great focus and use <strong>of</strong> these analysis and will be improv<strong>in</strong>g<br />
itself onwards.<br />
Figure 3-1 An <strong>in</strong>tensity map done by rapid <strong>in</strong>strumental technique. (Wald, 1999)<br />
Therefore, <strong>in</strong>tegrat<strong>in</strong>g an analysis program with a user-friendly <strong>in</strong>terface facilitates and greatly enhances<br />
the <strong>in</strong>terpretation <strong>of</strong> the dynamic behaviour <strong>of</strong> a particular site. The <strong>in</strong>tegration <strong>of</strong> SHAKE and<br />
ShakEdit <strong>in</strong>to an affordable, quality computer program is the next logical upgrade <strong>of</strong> the SHAKE computer<br />
program (Ordonez 2002). ShakEdit was orig<strong>in</strong>ally developed as a 16-bit, w<strong>in</strong>dows 3.1 applica-<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 39
tion that provided a graphical <strong>in</strong>terface for SHAKE. It was orig<strong>in</strong>ally conceived as an aid to the user <strong>in</strong><br />
the creation <strong>of</strong> the <strong>in</strong>put file and to the user <strong>in</strong> the creation <strong>of</strong> the <strong>in</strong>put file and the graphical display <strong>of</strong><br />
the program’s numeric output. In 1999, ShakEdit was upgraded to ShakEdit32 which is a 32 bit shell<br />
(Kahmann 2002). SHAKE was developed <strong>in</strong> 1991 by the University <strong>of</strong> California Berkeley, H. Bolton<br />
Seed, John Lysmer and Per B. Schnabel (Figure 3-2). This program computes the response <strong>in</strong> a<br />
system <strong>of</strong> homogenous, viscoelastic layers <strong>of</strong> <strong>in</strong>f<strong>in</strong>ite horizontal extent subjected to vertically travell<strong>in</strong>g<br />
shear waves.<br />
SHAKE<br />
SHAKEDIT<br />
EDUSHAKE<br />
SHAKE 2000<br />
PROSHAKE<br />
Figure 3-2: Diagram show<strong>in</strong>g the relationships between Shake s<strong>of</strong>tware.<br />
SHAKE2000 is a W<strong>in</strong>dows based, user-friendly computer program. The ma<strong>in</strong> objective <strong>in</strong> the development<br />
was to add new features to transform SHAKE <strong>in</strong>to an analysis tool for seismic analysis <strong>of</strong> soil<br />
deposits and earth structures. Apart form a learn<strong>in</strong>g tool for students, this version also serves to practitioners<br />
<strong>of</strong> geotechnical earthquake eng<strong>in</strong>eer<strong>in</strong>g as a tool to provide a first approximation <strong>of</strong> the dynamic<br />
response <strong>of</strong> a site. Depend<strong>in</strong>g upon the prediction <strong>of</strong> the site response, the practitioner judges<br />
whether more sophisticated dynamic modell<strong>in</strong>g is needed such as two or three-dimensional modell<strong>in</strong>g.<br />
The solution <strong>of</strong> a particular problem requires use <strong>of</strong> realistic ground motions, modell<strong>in</strong>g site dynamics<br />
and the <strong>in</strong>terpretation and prediction <strong>of</strong> soil behaviour subject to dynamic load<strong>in</strong>g. To help the eng<strong>in</strong>eer<br />
<strong>in</strong> the solution <strong>of</strong> this problem, SHAKE2000 was developed as a computer program that the practic<strong>in</strong>g<br />
eng<strong>in</strong>eer could employ to address geotechnical aspects <strong>of</strong> earthquake eng<strong>in</strong>eer<strong>in</strong>g <strong>of</strong> a project<br />
site. It <strong>in</strong>cludes the follow<strong>in</strong>g (Ordonez, 2002):<br />
• Numerous attenuation relationships<br />
• Design Spectra<br />
• Permanent Slope displacement calculation<br />
• Cyclic stress ratio (us<strong>in</strong>g Seed & Idriss ’71 or equivalent uniform shear stress)<br />
• Cyclic resistance ratio estimation<br />
• Settlement <strong>in</strong>duced by earthquake shak<strong>in</strong>g<br />
• PGA’s from the latitude and longitudes<br />
• Ground motion database (2500+) and motion file conversion utility<br />
• <strong>Response</strong> Spectra<br />
• Pr<strong>in</strong>t out <strong>in</strong> report style<br />
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<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
As mentioned by Ordonez (2002), the graphical display <strong>of</strong> the results is the most important feature<br />
when compared to the earlier versions.<br />
For the future improvements, the work<strong>in</strong>g group is work<strong>in</strong>g on the <strong>in</strong>clusion <strong>of</strong> liquefaction analysis<br />
us<strong>in</strong>g Cone Penetration data and shear wave velocity, the evaluation <strong>in</strong>duced ground deformation and<br />
on a feature that will facilitate the creation <strong>of</strong> output reports.<br />
3.3. Program Structure<br />
Before runn<strong>in</strong>g SHAKE2000, required <strong>in</strong>put parameters should be collected. These parameters <strong>in</strong><br />
pr<strong>in</strong>ciple can be obta<strong>in</strong>ed from borehole logg<strong>in</strong>gs and several other geophysical <strong>in</strong>vestigations such as<br />
seismic reflection method or electric surveys. In order to run the program you need m<strong>in</strong>imum <strong>in</strong>put<br />
parameters as follows,<br />
• <strong>Soil</strong> type<br />
• Thickness <strong>of</strong> the layer<br />
• Unit weight <strong>of</strong> the material<br />
• Shear modulus value <strong>of</strong> the material<br />
• Shear wave velocity <strong>of</strong> the material<br />
• Earthquake acceleration file<br />
Between velocity <strong>of</strong> shear wave and shear modulus there is compatibility. So, if you do not have one<br />
you can use the other. But both <strong>of</strong> them are generally difficult to obta<strong>in</strong>. For example, you can calculate<br />
us<strong>in</strong>g special equations for Gmax (Shear Modulus) with SPT N (Standard Penetration Test) values.<br />
Some <strong>of</strong> these equations are also found <strong>in</strong> Shake2000 s<strong>of</strong>tware the ones that could be easily used<br />
are:<br />
Gmax = 325 (N 60 ) * 0.68<br />
Gmax = 65 * N<br />
Here, SPT test determ<strong>in</strong>es the relative densities <strong>of</strong> noncohesive soils, Sands, or<br />
Silts; N value refers to the number <strong>of</strong> blows used <strong>in</strong> the test. This value could be corrected and then, it<br />
is called N 60 . Depend<strong>in</strong>g on the value type that the borehole record has one can use one <strong>of</strong> the above<br />
formulas.<br />
For the other <strong>in</strong>put parameters, thickness and the soil type are <strong>of</strong> course essential to know. And, the<br />
soil type can be def<strong>in</strong>ed more accurately us<strong>in</strong>g the option “dynamic soil properties”. This option uses<br />
standard damp<strong>in</strong>g and modulus equations already <strong>in</strong> the program that you can select from a list.<br />
Another important <strong>in</strong>formation for the required <strong>in</strong>put values is that they have to be converted to feet,<br />
feet per second, kips cubic foot and kips square foot. This conversion is needed if you are us<strong>in</strong>g <strong>in</strong>ternational<br />
system <strong>of</strong> units (SI) (Table 3-1). The program uses the generally used units <strong>in</strong> U.S. and/or<br />
U.K. for calculations.<br />
Parameter International System <strong>of</strong> Units (SI) Shake2000 Units<br />
Thickness 1 meter 3.28083 feet<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 41
Shear Wave Velocity 1 meter/second 3.28083 feet/second<br />
Unit Weight<br />
1 KN/m 3 (Kilo Newton per meter<br />
cube)<br />
0.0063 kcf (Kips<br />
(kilo pounds) cubic<br />
foot)<br />
Shear Modulus 1 Mpa (Mega Pascal) 20.88511 ksf<br />
(kilopound per<br />
square feet)<br />
Table 3-1 The conversion formulas used <strong>in</strong> the calculations for Shake2000.<br />
For the above-adopted formulas, Factors for conversion to the Metric System (SI) <strong>of</strong> Units article was<br />
used (Meritt, 1995).<br />
The Figure 3-8 represents a summarized methodology that is used to calculate the earthquake response<br />
<strong>in</strong> SHAKE2000. Here, it can be seen that the general steps are creat<strong>in</strong>g the file us<strong>in</strong>g several options<br />
then runn<strong>in</strong>g the SHAKE, and then process<strong>in</strong>g it. In the end display<strong>in</strong>g results, creat<strong>in</strong>g graphs and<br />
implement<strong>in</strong>g the graphs to the report takes place.<br />
In the ma<strong>in</strong> menu you can create, edit a file or you can process an output file, which has been already<br />
calculated (Figure 3-3). If you are creat<strong>in</strong>g a new file you go to the earthquake response analysis<br />
menu, which <strong>in</strong>cludes all the 10 options that could be used <strong>in</strong> an analysis (Figure 3-4). These 10 options<br />
are used to create the <strong>in</strong>put <strong>in</strong>formation file before runn<strong>in</strong>g the Shake.<br />
Figure 3-3 The ma<strong>in</strong> menu <strong>of</strong> Shake2000 s<strong>of</strong>tware.<br />
42<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
In the first option the dynamic soil properties are implemented to the materials with<strong>in</strong> the pr<strong>of</strong>ile you<br />
have (Figure 3-5). This <strong>in</strong>cludes the damp<strong>in</strong>g and modulus ratios for the specific type <strong>of</strong> material. For<br />
example if you have 4 materials (For example; Sand, Clay, Gravel and Rock) you create 4 damp<strong>in</strong>g<br />
and 4 shear modulus ratios. This is done by choos<strong>in</strong>g the best option from the list <strong>of</strong> the curves. The<br />
list <strong>in</strong>cludes the widely used and recognized references such as, for damp<strong>in</strong>g <strong>of</strong> a soil: “Damp<strong>in</strong>g <strong>Soil</strong><br />
with PI (Plasticity Index) =15 used from Vucetic & Dobry 1/1991” can be chosen. It is not that easy to<br />
choose the dynamic soil properties from the list, once you don’t have sufficient knowledge on the geotechnical<br />
properties <strong>of</strong> the materials. But it is possible to use medium values s<strong>in</strong>ce there are choices <strong>of</strong><br />
for <strong>in</strong>stance 3 types with different values. So the middle or 2 nd value will be generally proper for most<br />
<strong>of</strong> the soil conditions.<br />
Figure 3-4 The w<strong>in</strong>dow for choos<strong>in</strong>g and fill<strong>in</strong>g <strong>in</strong> the options for Shake2000.<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 43
Figure 3-5 The first option from the earthquake response analysis for the dynamic material properties.<br />
The second option creates the soil pr<strong>of</strong>ile us<strong>in</strong>g material types and layers (Figure 3-6). Here, you put<br />
<strong>in</strong>to operation the <strong>in</strong>put values <strong>of</strong> thickness; unit weight, damp<strong>in</strong>g and velocity <strong>of</strong> shear wave/ shear<br />
modulus for each layer. If there the shear wave velocity values are not available, <strong>in</strong>stead there are<br />
some geotechnical <strong>in</strong>formation (such as SPT-N values), then it is possible to use some <strong>of</strong> the equations<br />
which are <strong>in</strong> the s<strong>of</strong>tware.<br />
Figure 3-6 The w<strong>in</strong>dow where the soil pr<strong>of</strong>ile is implemented.<br />
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<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
The third option lets you to choose the proper <strong>in</strong>put motion for the study area. The list <strong>of</strong> accelerograms<br />
<strong>in</strong>cludes over 2500 real and simulated records from all over the world. You can also use other<br />
strong ground motion files. To do this you need to convert the <strong>in</strong>put strong ground motion file <strong>in</strong>to a<br />
file that SHAKE2000 can use. There is a converter to deal with this problem. But so far it can be seen<br />
that the list <strong>of</strong> earthquakes is generally sufficient to work for the analysis.<br />
The fourth option assigns the object motion to the sub-layers, which is generally the Rock material<br />
beneath the soil site. The <strong>in</strong>put signal could be assigned to the Rock or other sublayers that the soil<br />
pr<strong>of</strong>ile have. The fifth option is to def<strong>in</strong>e the number <strong>of</strong> iterations and stra<strong>in</strong> ratio. The iterations are<br />
for obta<strong>in</strong><strong>in</strong>g an error <strong>of</strong> less than 5-10 % <strong>in</strong> the calculations. As proposed <strong>in</strong> the help menu <strong>of</strong> the<br />
s<strong>of</strong>tware normally 3-5 iterations are sufficient (Ordonez, 2002) and stra<strong>in</strong> ratio depends on your magnitude<br />
<strong>of</strong> <strong>in</strong>put motion. Stra<strong>in</strong> ratio is given by the formula:<br />
Stra<strong>in</strong> Ratio = (Magnitude <strong>of</strong> the <strong>in</strong>put motion-1) /10<br />
The sixth option computes the acceleration at specified sub-layers. S<strong>in</strong>ce the top layer (surface) is the<br />
important layer for microzonation studies, the results for <strong>in</strong>termediate layers are not computed for this<br />
study but if needed the acceleration values can also be calculated for each <strong>in</strong>dividual layer contact.<br />
The seventh option calculates the time histories for shear stresses or stra<strong>in</strong>s at the top <strong>of</strong> the specified<br />
sub-layer. Each layer undergoes some stress and stra<strong>in</strong> depend<strong>in</strong>g on its properties and the <strong>in</strong>put motion<br />
signal properties. This could also be plotted aga<strong>in</strong>st the time that depends on the <strong>in</strong>put signal duration.<br />
Option eight calculates the response spectrum for different damp<strong>in</strong>g chosen (5, 10 and 20). This<br />
graph could be plotted <strong>in</strong> frequency or period. Option n<strong>in</strong>e is for amplification spectrum you can assign<br />
different sub-layers and outcrop or with<strong>in</strong> the soil options are also available to work. The last option<br />
computes the Fourier Spectrum. In simple words Fourier spectrum any periodic function that<br />
meets certa<strong>in</strong> conditions can be expressed as the sum <strong>of</strong> the s<strong>in</strong>usoids <strong>of</strong> different amplitude, frequency<br />
and phase (Kramer, 1996). The Fourier spectra show the frequency content <strong>of</strong> a motion very<br />
clearly.<br />
After fill<strong>in</strong>g <strong>in</strong> the options we are <strong>in</strong>terested <strong>in</strong>, we can run SHAKE. This takes a couple <strong>of</strong> seconds.<br />
After that we can use the display option, to see the analysis (Figure 3-7). One <strong>of</strong> the significant advantages<br />
<strong>of</strong> SHAKE2000 is that the user has a large variety <strong>of</strong> selections for display<strong>in</strong>g results. After creat<strong>in</strong>g<br />
the graph you can execute these <strong>in</strong>to your report.<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 45
Figure 3-7 The display <strong>of</strong> results for the analysis <strong>in</strong> table format.<br />
Above, a very general and simplified methodology <strong>of</strong> SHAKE2000 was mentioned <strong>in</strong> a short summary.<br />
However, it could be seen that the program has many options and one has to be very careful<br />
with all, <strong>in</strong> detail <strong>in</strong> order not to make any mistakes, because one <strong>of</strong> the drawback <strong>of</strong> the s<strong>of</strong>tware is<br />
that it does not allocate the error you have done.<br />
46<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
SHAKE 2000 METHODOLOGY<br />
MAIN MENU<br />
Create, Edit and<br />
Process files<br />
Plot Options<br />
Other <strong>Analysis</strong><br />
(Attenuation<br />
Relationships,<br />
Newmark Method etc.)<br />
EARTHQUAKE RESPONSE ANALYSIS<br />
OPTIONS<br />
1. Dynamic <strong>Soil</strong> Properties<br />
2. <strong>Soil</strong> Pr<strong>of</strong>ile<br />
3. Input (Object) Motion<br />
4. Assignment <strong>of</strong> Object<br />
Motion to a specific<br />
Sublayer<br />
5. Number <strong>of</strong> iterations &<br />
Stra<strong>in</strong> Ratio<br />
6. Computation <strong>of</strong><br />
Acceleration at Specified<br />
Sublayers<br />
7. Computation <strong>of</strong> Shear<br />
Stress or Stra<strong>in</strong> Time<br />
History<br />
8. <strong>Response</strong> Spectrum<br />
9. Amplification Spectrum<br />
10. Fourier Spectrum<br />
SHAKE<br />
Process<br />
Display<br />
<strong>Analysis</strong><br />
Plot<br />
Options<br />
Report<br />
Figure 3-8 SHAKE 2000 methodology (summarized).<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 47
4. Study Area<br />
4.1. Location<br />
Nepal is surrounded by Ch<strong>in</strong>a on the North, India on the south and west, Bhutan and Bangladesh on<br />
the east (Figure 4-1). It has a landlocked and strategic location between Ch<strong>in</strong>a and India. Although it<br />
conta<strong>in</strong>s eight <strong>of</strong> world's 10 highest peaks, <strong>in</strong>clud<strong>in</strong>g Mount Everest; the world's tallest, which is on<br />
the border with Ch<strong>in</strong>a, it also has flat river areas- so called Terai. Terai lies to the south hav<strong>in</strong>g an altitude<br />
<strong>of</strong> 70 m above sea level. Economy is depended on tourism and textile. Almost half <strong>of</strong> the population<br />
is liv<strong>in</strong>g below the poverty l<strong>in</strong>e and is one <strong>of</strong> the least developed countries <strong>in</strong> the world. Its total<br />
area is 140,800 and % 20.27 <strong>of</strong> the area is arable.<br />
Figure 4-1 Small map show<strong>in</strong>g Asia, the rectangle <strong>in</strong>dicates Nepal. Also, Lalitpur is <strong>in</strong>dicated <strong>in</strong> Nepal<br />
map.<br />
Kathmandu is the capital <strong>of</strong> the country and has the highest population <strong>of</strong> 1,093,414 (2001). It is surrounded<br />
by high hills and forms a valley, <strong>in</strong>clud<strong>in</strong>g Lalitpur, Bhaktapur and Patan cities. Kathmandu is<br />
almost <strong>in</strong> the middle <strong>of</strong> the country and has an elevation around 1400 m surrounded by some 2100 m<br />
mounta<strong>in</strong>s and peaks reach<strong>in</strong>g up to 2765 m.<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 49
Lalitpur is on the south <strong>of</strong> Kathmandu city; the Bagmati River separates them. The border is almost<br />
unseen, and the separation is more on governmental issues (Figure 4-2). While Kathmandu is the metropolitan<br />
city, Lalitpur is a sub-metropolitan city with smaller population <strong>of</strong> approximately 336.677.<br />
The coord<strong>in</strong>ates <strong>of</strong> the study area are 27 o 32’58. 51’’/ 6 o 21’02. 15’’ NW and 27 o 30’41. 00’’/ 6 o 23’52.<br />
75’’ SE with an area <strong>of</strong> 15 square kilometres. The reason for choos<strong>in</strong>g Lalitpur sub-metropolitan city<br />
is it was chosen for the SLARIM projects case study area and also it fulfilled the data-lack<strong>in</strong>g problem<br />
better than Kathmandu. Not only data <strong>in</strong>sufficiency but also it also ma<strong>in</strong>ta<strong>in</strong>ed the required organizational<br />
support <strong>in</strong> the region.<br />
Figure 4-2 Study area; Lalitpur. North <strong>of</strong> Lalitpur is Kathmandu City.<br />
4.2. Geology<br />
Nepal has one <strong>of</strong> the most remarkable geological formations throughout the world; it emerges from the<br />
Himalayan Mounta<strong>in</strong> Range to the flat river; Ganga Pla<strong>in</strong>. The Himalayas were formed by a collision<br />
between the Indian and Tibetan plate that started about 50 million years ago. Hav<strong>in</strong>g the some <strong>of</strong> the<br />
highest peaks <strong>of</strong> the world it can be derived that the region is tectonically very active. The com<strong>in</strong>g together<br />
<strong>of</strong> two lithospheric plates and form<strong>in</strong>g <strong>of</strong> the mounta<strong>in</strong>s has a speed <strong>of</strong> 2 cm/year <strong>in</strong> the region.<br />
Not only collisions <strong>of</strong> the cont<strong>in</strong>ent appear <strong>in</strong> Nepal, but also subduction takes place between the Indian<br />
subcont<strong>in</strong>ent and Eurasia form<strong>in</strong>g convergent boundaries. Subduction happens where; dense oceanic<br />
crusts are pushed under the cont<strong>in</strong>ental plates, which are lighter <strong>in</strong> density.<br />
The major fault systems are parallel to the Himalayan arc formed by the collision and subduction. India,<br />
Nepal and Bangladesh are the countries that are associated with the Himalayan Frontal Arc with<br />
high seismic activity. The fault systems <strong>in</strong> the Himalayan arc are divided <strong>in</strong>to four major systems:<br />
• Himalayan Frontal Fault System (HFF)<br />
• Ma<strong>in</strong> Boundary Thrust Fault System (MBT)<br />
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<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
• Ma<strong>in</strong> Central Thrust Fault System (MCT)<br />
• Indus Suture Zone (ISZ)<br />
The movement <strong>of</strong> these major active fault systems and the branches <strong>of</strong> them creates the earthquakes <strong>in</strong><br />
the region.Shown <strong>in</strong> Figure 4-3, till the boundary <strong>of</strong> MBT, the region is called Sub-Himalayas. From<br />
that boundary to MCT Lesser-Himalayas and from the MCT boundary to the small fault is called<br />
Higher-Himalayas and the last part to the north is called Trans-Himalayas. The boundary between the<br />
Higher-Himalayas and the Trans –Himalayas also gives the boundary <strong>of</strong> the Indian Plate and the Eurasian<br />
Plate.<br />
Figure 4-3 From south to north it can be seen, ma<strong>in</strong> frontal fault system, ma<strong>in</strong> boundary trust and the<br />
ma<strong>in</strong> central trust boundaries. The Indus Suture Zone starts from the border <strong>of</strong> north side (Avouac,<br />
Boll<strong>in</strong>ger et al. 2001).<br />
Nepal topography could be divided <strong>in</strong>to three regions; Himalayan Mounta<strong>in</strong> Range, Mahabharat range<br />
<strong>in</strong> the middle and the pla<strong>in</strong> area Terai. Terai has the 17% <strong>of</strong> the land and it’s altitude changes from 100<br />
to couple <strong>of</strong> hundred meters. This lowland has fertile soils and therefore it is used for agriculture and is<br />
well known for its national parks <strong>in</strong> this region. Mahabharat range covers the 65% <strong>of</strong> the land. The<br />
altitude <strong>of</strong> this region changes from 500 to 3000 meters. And the Himalayan range has the 8 <strong>of</strong> the<br />
highest peaks <strong>of</strong> the world; which are Mt. Everest (8848m), Kanchanjunga (8586m), Lhotse (8516m),<br />
Cho Oyu (8201m) and Dhaulagiri (8167m), Mt. Makalu (8463m), Manaslu (8163m) and Annapurna I<br />
(8091m).<br />
Kathmandu valley lies <strong>in</strong> the middle <strong>of</strong> Nepal and is <strong>in</strong> the south <strong>of</strong> the higher Himalayan range and<br />
has the Mahabharat Lekh range on its south. It is an <strong>in</strong>tramontane bas<strong>in</strong> that was formed dur<strong>in</strong>g Quaternary<br />
period. The uplift <strong>of</strong> the Mahabharat Lekh range is believed to cause the lake formation <strong>in</strong> the<br />
bas<strong>in</strong>. The southward dra<strong>in</strong>age has stopped because <strong>of</strong> this uplift and formed very thick reach<strong>in</strong>g up to<br />
~545 m river and lake sediments. The lake had been dried and dra<strong>in</strong>ed out from a gorge that is cut by<br />
the Bagmati River. The sediments <strong>of</strong> the Kathmandu valley have a wide variety <strong>in</strong> category. The<br />
northern part <strong>of</strong> the valley consists <strong>of</strong> riverbed layered deposits <strong>of</strong> Clay, Silt, Sand and Gravel. Southern<br />
part has mostly Clay and Silt with coarse sediment layers (Yadav, S<strong>in</strong>gh et al. 1994). The<br />
unconsolidated sediments <strong>of</strong> the valley consists <strong>of</strong> f<strong>in</strong>e-gra<strong>in</strong>ed lake deposits <strong>of</strong> late Tertiary to<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 51
solidated sediments <strong>of</strong> the valley consists <strong>of</strong> f<strong>in</strong>e-gra<strong>in</strong>ed lake deposits <strong>of</strong> late Tertiary to Quaternary<br />
(5 million years ago or younger).<br />
Kathmandu valley forms a syncl<strong>in</strong>e <strong>in</strong> the Lesser Himalayas. On the north range <strong>of</strong> this syncl<strong>in</strong>e lies<br />
the Gneisses <strong>of</strong> the Shivapuri Lekh and on the south the granitic Rocks <strong>of</strong> the Mahabharat Range<br />
(Stöckl<strong>in</strong> 1986). In the Valley there are small anticl<strong>in</strong>es and syncl<strong>in</strong>es bordered by faults runn<strong>in</strong>g EW<br />
direction (Dill, Kharel et al. 2001). In general the valley has recent Quaternary deposits, but it also <strong>in</strong>cludes<br />
the formations Tistung, Sopyang and Chandragiri def<strong>in</strong>ed by Bajracharya, 2003. On the north<br />
<strong>of</strong> Valley, Rocks are def<strong>in</strong>ed as Gneiss. The west boundary <strong>in</strong>cludes the Tistung, Chitlang and Ghanapokhara.<br />
To the east Tistung and Chandragiri takes place on the boundaries <strong>of</strong> the recent deposits and<br />
the hills surrounded (Figure 4-4). Tistung Formation has; dull green grey coloured phyllites, p<strong>in</strong>k purplish<br />
th<strong>in</strong> bed Sandstone with Sandy limestones ripple marks, Clay cracks, worm tracks are abundant.<br />
And, pebbly beds near base can be seen. Chandragiri Formation has; light f<strong>in</strong>e-gra<strong>in</strong>ed crystall<strong>in</strong>e<br />
limestones, partly siliceous thick- to massively bedded white quartzites <strong>in</strong> upper parts. Chitlang Formation<br />
has; Dark slates with white quartzites at the base and impure limestones. Ghanapokhara Formation<br />
is def<strong>in</strong>ed as, black grey shales with black limestones th<strong>in</strong> calcareous slate, grey dolomitic limestones,<br />
black carbonaceous slates with th<strong>in</strong> calcareous Sandstone beds and grey to black dolomitic<br />
limestone (Bajracharya 2003).<br />
Though the surround<strong>in</strong>g <strong>of</strong> the Valley is def<strong>in</strong>ed <strong>in</strong> detail and the <strong>in</strong>side <strong>in</strong> general, Lalitpur area has<br />
been def<strong>in</strong>ed us<strong>in</strong>g river terrace levels <strong>in</strong> the JICA’s report on earthquake disaster assessment and database<br />
system <strong>in</strong> 2002. They have def<strong>in</strong>ed 1, 2 and 3 types <strong>of</strong> terrace deposits, talus deposits and recent<br />
river deposits (Figure 4-4). Also from the work done by the ICIMOD and R. Bajracharya 2003, the<br />
area was def<strong>in</strong>ed as alluvium; boulders, Gravels, Sands and Clays from Quaternary period. In general<br />
the boreholes <strong>in</strong> the study area shows that the ma<strong>in</strong> thick sediment type as Clay. On the north side <strong>of</strong><br />
the area, thick Clays and Gravely Sand can be found. Northwest side has less thick Clay deposits with<br />
some Sandy Gravel at the base. Central part consists <strong>of</strong> Silt and thick Clays with boulder and Gravels<br />
at the base. Southeast part has ma<strong>in</strong>ly Sandy Clay and Sandy Silt with some Sand close to surface but<br />
there is a sudden change <strong>in</strong> the stratigraphy laterally when we compare this borehole with its<br />
neighbour<strong>in</strong>g one, which consists <strong>of</strong> ma<strong>in</strong>ly Clay and Silty Sand. East section has thick Clay deposits<br />
over the Sands.<br />
In the study <strong>of</strong> National Build<strong>in</strong>g Code Development Project 5 ma<strong>in</strong> and active faults have been identified<br />
(Yadav, S<strong>in</strong>gh et al. 1994). Pleistocene to Holocene period aged sediments was moved by these<br />
faults. Three <strong>of</strong> them had been named, which are Thankot, Basoigaon, and Bungamati. One <strong>of</strong> the<br />
other two faults is a normal fault. It is found on the flood pla<strong>in</strong> <strong>of</strong> the Bagmati River <strong>in</strong> the Pharp<strong>in</strong>g<br />
area. The other runs through the northern foothills <strong>of</strong> the Kirtipur- Chobhar Ridge, which is as close as<br />
5 km to Kathmandu city. This is also estimated a normal fault. Thankot fault is a normal fault that<br />
strikes N-NW and truncates the toe <strong>of</strong> the alluvial fan on the slopes <strong>of</strong> the Chandragiri Range. The<br />
length <strong>of</strong> it is 8 km. Basigaon fault is probably the conjugate <strong>of</strong> the Thankot fault. It has a length <strong>of</strong> 3<br />
km and it has a similar strike. Bungamati fault is close to Lalitpur about 5 km and has an estimated<br />
length <strong>of</strong> 26 km. It has a strike <strong>of</strong> N-NE form the channel <strong>of</strong> the Bagmati River to the village <strong>of</strong> Sunakothi.<br />
52<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
Geology Map <strong>of</strong> Kathmandu Valley.<br />
(Department <strong>of</strong> M<strong>in</strong>es and Geology)<br />
W<br />
N<br />
E<br />
S<br />
Geopoly.shp<br />
Chandragiri formation<br />
Chitlang formation<br />
Godavari Limestone<br />
Kulekhani Formation<br />
Markhu Formation<br />
Recent river deposit<br />
Sheopuri Formation<br />
Sopyang formation<br />
Talus deposit<br />
Terrace I deposit<br />
Terrace II deposit<br />
Terrace III deposit<br />
Terrace IV deposit<br />
Terrace V deposit<br />
Tistung Formation<br />
10 0 10 20 Kilometers<br />
Study Area, Lalitpur Geology Map<br />
W<br />
N<br />
E<br />
S<br />
Terrace IV deposit<br />
Terrace I deposit<br />
Terrace II deposit<br />
Terrace III deposit<br />
Talus deposit<br />
Recent river deposit<br />
Lalitpur Boundary<br />
Geology Legend<br />
Chandragiri formation<br />
Chitlang formation<br />
Godavari Limestone<br />
Kulekhani Formation<br />
Markhu Formation<br />
Recent river deposit<br />
Sheopuri Formation<br />
Sopyang formation<br />
Talus deposit<br />
Terrace I deposit<br />
Terrace II deposit<br />
Terrace III deposit<br />
Terrace IV deposit<br />
Terrace V deposit<br />
Tistung Formation<br />
3 0 3 Kilometers<br />
Figure 4-4 Geology map <strong>of</strong> the Kathmandu Valley and the Lalitpur city.<br />
There are other faults with<strong>in</strong> the region but they are outside <strong>of</strong> Kathmandu about 20- 50 km. There are<br />
three <strong>of</strong> them with estimated potential magnitude level. First one is Kalphu Khola Fault to the northwest<br />
<strong>of</strong> the Valley is <strong>in</strong>terpreted that it could generate a maximum Richter’s magnitude <strong>of</strong> 6.9. Second<br />
fault, Kulikhani is also estimated to generate the same magnitude. Third one, which lies about 35km<br />
SE <strong>of</strong> Kathmandu, could generate 7.1 Richter’s magnitude. Any <strong>of</strong> these faults movement will create<br />
effects to the Valley’s cities.<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 53
4.3. <strong>Seismic</strong>ity<br />
Nepal is with<strong>in</strong> the seismic zone from Java-Myanmar-Himalayas-Iran and Turkey, where many destructive<br />
earthquakes happens. The earthquakes that occurred <strong>in</strong> the Himalayan region are the biggest<br />
<strong>in</strong>tra-cont<strong>in</strong>ental earthquakes <strong>of</strong> the 20 th century <strong>in</strong>clud<strong>in</strong>g the Kangra-India 1905, Bihar-Nepal 1934<br />
and Assam-India 1950. These earthquakes had magnitudes around 8.5. So far, the seismological studies<br />
showed that the big gap <strong>in</strong> the seismicity refers to Western and Central Nepal (Karanth 2002). This<br />
situation makes seismic hazard <strong>in</strong> Kathmandu valley, which is central Nepal and the western part <strong>of</strong><br />
the country <strong>in</strong> high risk for the future earthquakes (Figure 4-5).<br />
Figure 4-5 Taken from Bilham et al (2001) this figure shows the seismic gap regions and the potential<br />
magnitudes for the Himalayan region. It can be seen that Kathmandu has a potential slip <strong>of</strong> 4 m for certa<strong>in</strong><br />
and even more is possible.<br />
In Figure 4-5, the years that represent the orange circular areas are referr<strong>in</strong>g to the high magnitude<br />
earthquakes happened <strong>in</strong> the Himalayan arc region. Below a table is given for their magnitude and<br />
time <strong>in</strong>formation (Table 4-1).<br />
Year Location Magnitude (Ms)<br />
1803 Kumaon 8?<br />
1833 Kathmandu 7.7<br />
1885 Kashmir 7<br />
1905 Kangra 7.8<br />
1934 Bihar/Nepal 8.4<br />
1947 Assam 7.7<br />
54<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
1950 Arunchal Pradesh 8.5<br />
Table 4-1 Important high magnitude earthquakes happened <strong>in</strong> the Himalayan region.<br />
Kathmandu valley has experienced many destructive earthquakes with<strong>in</strong> history, such as 1833 with a<br />
magnitude <strong>of</strong> 7.5, 1934 with magnitude 8.4 and 1988 with 6.8 (Figure 4-6). One <strong>of</strong> the earliest <strong>in</strong>formation<br />
obta<strong>in</strong>ed for the valley is <strong>in</strong> 1255 <strong>in</strong> a report <strong>of</strong> the earthquake, it is said that 1/3 <strong>of</strong> the K<strong>in</strong>gdom<br />
<strong>of</strong> Nepal was perished. Additionally <strong>in</strong> 1408, 1681 and 1810 earthquakes had been reported with<br />
a Modified Intensity values rang<strong>in</strong>g around IX and X (Yadav, S<strong>in</strong>gh et al. 1994). It can be seen that<br />
the effects <strong>of</strong> these earthquakes had been devastat<strong>in</strong>g. The earthquake <strong>of</strong> 1934 had given a lot <strong>of</strong> damage<br />
to the Kathmandu valley and the Terai region though it was located <strong>in</strong> the city Cha<strong>in</strong>pur <strong>in</strong> the<br />
east. It has been estimated that around 1.100.000 houses were damaged <strong>in</strong> this earthquake. Also,<br />
Yadav, S<strong>in</strong>gh et al has mentioned that (1994) <strong>in</strong> the valley Bhaktapur had suffered more damage than<br />
the other cities <strong>in</strong> the Valley (Yadav, S<strong>in</strong>gh et al. 1994).<br />
1934 earthquake had been very damag<strong>in</strong>g to the Kathmandu Valley though it was 240 km away. The<br />
valley experienced <strong>in</strong>tensities <strong>of</strong> IX-X on the Modified Mercalli scale. About 8500 casualties were<br />
reported and 80.000 houses were damaged. The Valley itself had the 4300 people dead and 12500<br />
houses were damaged out <strong>of</strong> these numbers (Yadav, S<strong>in</strong>gh et al. 1994). Also the 1988, Udayapur<br />
earthquake (Magnitude: 6.6) that was aga<strong>in</strong> located relatively far from the Valley (1665 km) had been<br />
felt <strong>in</strong> the Valley. A few build<strong>in</strong>gs were damaged and several people were <strong>in</strong>jured. These cases had<br />
proved that Kathmandu Valley had unfavourable characteristics for the earthquake hazard.<br />
In September 2002, Pandey et al produced the seismic hazard map <strong>of</strong> Nepal. They have collected<br />
around 5000 local earthquakes <strong>in</strong> the microseismic database. The study had collected all the earthquakes<br />
greater than 2 between 1994 and 2002. In Figure 4-6 can also be seen the cluster<strong>in</strong>g <strong>of</strong> the microseismic<br />
epicentral distribution is ma<strong>in</strong>ly parallel to the Himalayan Frontal Arc. This region was<br />
divided <strong>in</strong>to eastern and western for their study. The computation between the local magnitude (Ml)<br />
(or undef<strong>in</strong>ed magnitude Mo) and the moment magnitude (Mw) was done by us<strong>in</strong>g the Ambrassey,<br />
2000 formula. Us<strong>in</strong>g the formula given;<br />
Log (Mo) = 19.08 +Ms<br />
Mw = (2/3) log (Mo) – 10.73<br />
The reason to convert local magnitude to the moment one is, that it is a better measure <strong>of</strong> the true size<br />
<strong>of</strong> an earthquake and is recommended to be used with the attenuation relationships (Erdik, Biro et al.<br />
1999). The magnitude-frequency relation for the earthquakes is given by the formula:<br />
Log N = constant – b Ms<br />
N, is the number <strong>of</strong> earthquakes with magnitudes equal to M or greater than M. M is “Ms” <strong>in</strong> the formula<br />
(surface wave magnitude). This formula represents that there is a close relationship between surface<br />
wave magnitude and N. B <strong>in</strong> the formula represents relatively small and large earthquakes measure.<br />
If b has a high value then small earthquakes are more frequent <strong>in</strong> the area. And if the value is<br />
small then the large earthquakes are more frequent <strong>in</strong> the area. For this formula the b values are calculated<br />
as 1.7 ± 0.2 for a given magnitude <strong>of</strong> 5 by the study <strong>of</strong> Pandey et al. They have also calculated<br />
the rate <strong>of</strong> activity for this earthquake, which is approximately equal to one event per year.<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 55
Figure 4-6 Map show<strong>in</strong>g, seismic data for the years between 04/01/1995 and 10/12/1999, geodetic measurements<br />
and major geological structures with (MFT, MBT, MCT) (Catt<strong>in</strong> and Avouac 2000).<br />
5. <strong>Seismic</strong> <strong>Response</strong> <strong>Analysis</strong> For<br />
Lalitpur, Nepal<br />
5.1. Ground <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> Methodology<br />
This chapter describes the <strong>in</strong>put data, procedures and methods used for the ground response analysis<br />
applied <strong>in</strong> the Lalitpur study area. Ground response analysis could be done <strong>in</strong> several ways depend<strong>in</strong>g<br />
56<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
on the availability <strong>of</strong> the data <strong>in</strong> the site. If there is a dense network <strong>of</strong> boreholes <strong>in</strong> the site, then it is<br />
possible to create 1D <strong>in</strong>formation and this could be used <strong>in</strong> the analysis <strong>of</strong> Shake2000 or other programs.<br />
It is also possible to obta<strong>in</strong> geotechnical <strong>in</strong>formation through geophysical <strong>in</strong>vestigation methods<br />
(such as, seismic and electrical methods), and these provide 2D cross-sections with geotechnical<br />
<strong>in</strong>formation (layer thickness, shear wave velocity etc). Another method to do a ground response analysis/modell<strong>in</strong>g<br />
is to use a generalized 2,5 or 3D subsurface model. Though, there were some boreholes<br />
<strong>in</strong> the region (17), the number was not sufficient to model the area us<strong>in</strong>g <strong>in</strong>terpolation techniques. And<br />
geophysical <strong>in</strong>vestigations were not available from the fieldwork or the literature. On the other hand,<br />
the 2,5 D subsurface geology was available to use (Piya, 2004). Conclusively, this subsurface geology<br />
model was used to do the modell<strong>in</strong>g. The PGA, MMI and resonance maps are produced us<strong>in</strong>g this subsurface<br />
geology model and runn<strong>in</strong>g them <strong>in</strong> Shake2000. To understand the reliability <strong>of</strong> the models,<br />
the boreholes were also used to make a crosscheck. The results are discussed <strong>in</strong> this chapter.<br />
Ground response modell<strong>in</strong>g has been carried out us<strong>in</strong>g two methodologies. The first methodology focused<br />
on the use <strong>of</strong> the actual borehole <strong>in</strong>formation <strong>in</strong> the soil response modell<strong>in</strong>g, whereas the second<br />
methodology uses the results from the generalized soil pr<strong>of</strong>iles and the GIS based layer models developed<br />
by Piya (2004). In the first methodology two models are used with 3 different earthquake scenarios.<br />
The second methodology used the generalized soil pr<strong>of</strong>ile for the Lalitpur region and resulted <strong>in</strong><br />
different maps (PGA, MMI and Resonance etc.) for the worst earthquake scenario.<br />
5.1.1 Methodology 1: <strong>Modell<strong>in</strong>g</strong> based on available borehole data<br />
Methodology 1 uses two models (see Figure 5-2), which are expla<strong>in</strong>ed below.<br />
Model 1: Us<strong>in</strong>g actual borehole data<br />
The borehole database for Kathmandu valley generated by Piya (2004) conta<strong>in</strong>s 17 boreholes for the<br />
Lalitpur area. Table 5.1 shows the deep and shallow boreholes with their depths and Figure 5-1 shows<br />
their locations. Table 5-2 gives the po<strong>in</strong>ts and their thickness values from the generalized pr<strong>of</strong>ile.<br />
Three boreholes (Borehole ID: C291, B1 and C288) were <strong>in</strong>itially <strong>in</strong>cluded <strong>in</strong> the analysis but no<br />
proper results could be obta<strong>in</strong>ed because the ground motion caused shear stra<strong>in</strong>s greater than the shear<br />
stra<strong>in</strong> used to def<strong>in</strong>e the material properties <strong>in</strong> the analysis. Several analyses were done <strong>in</strong> order to<br />
overcome this situation but they did not work. On the other hand B1 was corrected for the shear stra<strong>in</strong>s<br />
us<strong>in</strong>g other reduction modulus values and work<strong>in</strong>g well, but this result came too late to implement it <strong>in</strong><br />
the analysis (Ordonez, personal communication). 14 Boreholes <strong>in</strong>cluded; thickness values for each<br />
layer with stratigraphic <strong>in</strong>formation (Table 5-1). Four <strong>of</strong> them (C 296, SPT 6; SPT 39 and SPT 25)<br />
were only a few meters deep. On the other hand, they (C296 and SPT 6) were the ones with much<br />
more geotechnical <strong>in</strong>formation than the others. Basically the geotechnical <strong>in</strong>formation <strong>in</strong> the borehole<br />
logs consisted <strong>of</strong> SPT-N values, void ratio, or unit weight (dry, saturated) etc. From borehole SPT-6,<br />
the SPT-N values and from borehole C296, SPT N-corrected values were used. SPT (Standard Penetration<br />
Test) is a soil sampl<strong>in</strong>g method called Standard Penetration Test, which is a commonly<br />
standardised site <strong>in</strong>vestigation test method to determ<strong>in</strong>e the relative densities <strong>of</strong> noncohesive soils,<br />
such as Sands, or Silts. The procedure is as follows: At the bottom <strong>of</strong> a borehole a cyl<strong>in</strong>drical sampler<br />
is driven with standardised dimensions (ASTM 2004). To determ<strong>in</strong>e the number <strong>of</strong> blows a drive<br />
hammer (A short tube like device designed to be forced, without rotation) is used. The blow count,<br />
which is the N value, is obta<strong>in</strong>ed by the total blows required from a hammer, over the <strong>in</strong>terval 150 to<br />
450 mm per 0.3 m. The numbers <strong>of</strong> blows are counted where it requires the hammer to move from 150<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 57
m. The numbers <strong>of</strong> blows are counted where it requires the hammer to move from 150 to 450 mm and<br />
it is repeated every 0.3 meters. In liquefaction analysis and foundation design the N-value is used as a<br />
basis. It is possible to improve the N-values us<strong>in</strong>g a correction formula:<br />
N’= 15 + ½(N+15)<br />
Where: N = N value and N’ = corrected N value. If the test is done <strong>in</strong> very f<strong>in</strong>e Sand or Silty Sand below<br />
the water table the measured N value, if greater than 15 (derived from laboratory tests), should be<br />
corrected (Craig 1987). This formula was applied to C296 borehole us<strong>in</strong>g the exist<strong>in</strong>g N-values.<br />
Shallow Boreholes<br />
Deep Boreholes<br />
ID code Depth (m) ID code Depth (m)<br />
C 40 12 B 23 304.19<br />
C 296 2.45 B 25 136.12<br />
SPT 6 1.45 DMG 13 298<br />
SPT 39 6.5 BHD 3 195<br />
PR 16 48 P 29 174<br />
SPT 25 4.45 P 37 350<br />
B 24 60 AG 68 189<br />
Table 5-1 Actual Deep and shallow boreholes.<br />
Po<strong>in</strong>t ID<br />
Thickness <strong>of</strong> the<br />
post-lake<br />
deposits (m)<br />
Thickness <strong>of</strong><br />
the lake deposits<br />
(m)<br />
Thickness <strong>of</strong><br />
the pre- lake<br />
deposits (m)<br />
Total<br />
Thickness (m)<br />
B24 & B25 (Po<strong>in</strong>t No:8) 3 62 7 72<br />
SPT39 & PR16 (14) 3 91 79 173<br />
BHD 3 (44) 2 133 80 215<br />
SPT6 & AG68 (24) 16 85 126 227<br />
C 40 (10) 14 118 106 238<br />
C 296 (16) 9 50 184 243<br />
B 23 (43) 30 141 95 266<br />
P 29 (2) 1 173 149 323<br />
DMG 13 (29) 1 161 246 408<br />
SPT25 & P37 (58) 43 36 419 498<br />
Table 5-2 The borehole po<strong>in</strong>ts and their correspond<strong>in</strong>g thickness’ read from the generalized pr<strong>of</strong>ilee.<br />
58<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
For each borehole an excel sheet was prepared. These sheets <strong>in</strong>volved the conversion from SI units to<br />
the units that Shake2000 uses (See Appendix), the <strong>in</strong>terpreted shear wave velocity, unit weight, thickness<br />
and soil types. In the table shown below (Table 5-3), only the unit weight and two sets <strong>of</strong> shear<br />
wave velocities are <strong>in</strong>volved. Damp<strong>in</strong>g was selected as 5% for the whole analysis. In general damp<strong>in</strong>g<br />
ratio is accepted as 5, 10 or 20 percent (Kramer 1996). It is assumed that 5 percent will be sufficient<br />
for the analysis. And thickness varies <strong>in</strong> every layer.<br />
<strong>Soil</strong> Type<br />
Unit Weight<br />
Shear wave<br />
velocity (m<strong>in</strong>imum<br />
value used)<br />
Shear wave velocity<br />
(maximum values<br />
used)<br />
KN/m3 Kcf M/s F/s M/s F/s<br />
<strong>Soil</strong> 15 0.10 250 820 250 820<br />
Clay 16 0.10 300 984 600 1968<br />
Silt 17 0.11 450 1476 800 2625<br />
Sand 18 0.11 600 1969 1200 3937<br />
Gravel 20 0.12 1700 5577 1700 5577<br />
Boulders 21 0.13 1500 4921 2000 6562<br />
Rock 22 0.14 3000 9842 3000 9842<br />
Table 5-3 Assumed shear wave velocity values for different soil types.<br />
Accord<strong>in</strong>g to discussions held with experts on the range <strong>of</strong> shear wave velocities and the unit weight<br />
values, the first set <strong>of</strong> shear wave values was produced. The unit weight values were kept constant for<br />
both <strong>of</strong> the sets. The unit weight values could have been analysed <strong>in</strong> more detail us<strong>in</strong>g the water table<br />
<strong>in</strong>formation, by us<strong>in</strong>g dry unit weight above and saturated unit weight below the water table. But, this<br />
would also change the assumptions balance between the parameters. For <strong>in</strong>stance it would be better if<br />
we could estimate the shear wave velocities and its value changes with depth. But if this is done, then<br />
the other <strong>in</strong>puts like unit weight should also be more accurately estimated through the assign<strong>in</strong>g <strong>of</strong><br />
values.<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 59
Figure 5-1 Map show<strong>in</strong>g borehole locations and the total thickness <strong>of</strong><br />
the soil layer.<br />
60<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
GROUND RESPONSE MODELLING<br />
METHOD 1<br />
Model 1<br />
Model 2<br />
Input Parameters<br />
14 boreholes with def<strong>in</strong>ed depth and<br />
soil type <strong>in</strong>formation.<br />
Input Parameters<br />
•14 po<strong>in</strong>ts with the same coord<strong>in</strong>ates<br />
thickness read from the generalized map.<br />
•<strong>Soil</strong> type, unit weight and shear wave velocity are<br />
def<strong>in</strong>ed by generalization from literature.<br />
•Two different sets <strong>of</strong> shear wave velocity are used for<br />
the region.<br />
•Damp<strong>in</strong>g is chosen %5 for all soil types.<br />
Borehole def<strong>in</strong>ed<br />
soil pr<strong>of</strong>iles.<br />
4 layer simplified<br />
soil pr<strong>of</strong>ile.<br />
Name <strong>of</strong> the<br />
earthquake<br />
Mae Center<br />
RR 2B<br />
Synthetic<br />
Los Angeles<br />
Simulated<br />
SAC Steel<br />
Northridge<br />
1994<br />
Input Motion<br />
Magnitude<br />
8<br />
7.1<br />
6.7<br />
Distance<br />
48 km<br />
(hypocentral<br />
distance)<br />
17.5 km<br />
(epicentral)<br />
6.4 km<br />
(epicentral)<br />
•Model 1 Outputs<br />
•Peak Ground Acceleration Values<br />
•<strong>Response</strong> Spectrum<br />
•Amplification Spectrum<br />
•Model 2 Outputs<br />
•Peak Ground Acceleration Values<br />
•<strong>Response</strong> Spectrum<br />
•Amplification Spectrum<br />
Comparison <strong>of</strong> the<br />
two models outputs.<br />
Figure 5-2 Flowchart <strong>of</strong> the method 1.<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 61
For the other <strong>in</strong>put parameter, strong motion record, which is necessary to run Shake2000, three earthquake<br />
scenarios were chosen. In order to estimate the ground response <strong>in</strong> a region, the best would be<br />
hav<strong>in</strong>g actual records from the area. But the s<strong>in</strong>gle set <strong>of</strong> available acceleration records obta<strong>in</strong>ed from<br />
Kathmandu Valley was not sufficient to use. To overcome this, Shake2000 s<strong>of</strong>tware’s database could<br />
be used. S<strong>in</strong>ce Shake2000 has 2500 scenario earthquakes <strong>in</strong> the s<strong>of</strong>tware, it should be possible to<br />
choose an earthquake that represents the regional characteristics. Selection procedure generally depends<br />
on the magnitude and distance parameters, though it is advised to use data from similar tectonic<br />
sett<strong>in</strong>g, fault properties and attenuation charactreristics. Because <strong>of</strong> the unavailability <strong>of</strong> such <strong>in</strong>put<br />
motions, the approach was to use the exist<strong>in</strong>g database <strong>in</strong> Shake2000. These scenarios are based on<br />
discussions with Nepalese geologists, seismologists and other scientists who worked <strong>in</strong> this region<br />
(Avouac, personal communication). From the Department <strong>of</strong> M<strong>in</strong>es and Geology (DMG), the acceleration<br />
records for a real earthquake were also obta<strong>in</strong>ed. There were two stations that recorded one <strong>in</strong><br />
DMG and one <strong>in</strong> the Rock outcrop called Kakani. The response spectra were also obta<strong>in</strong>ed <strong>in</strong> paper<br />
format but they are lack<strong>in</strong>g one direction (Z; vertical component is miss<strong>in</strong>g). The earthquake’s properties<br />
(magnitude, distance and location etc.) were also not certa<strong>in</strong>; enough <strong>in</strong>formation could not be<br />
gathered from the scientists <strong>of</strong> the national seismological centre. The file <strong>of</strong> the accelerograph can be<br />
found <strong>in</strong> the appendices <strong>in</strong> digital. But, these records did not have sufficient data <strong>in</strong> order to implement<br />
them <strong>in</strong>to the s<strong>of</strong>tware. For example they did not specify the acceleration units or direction <strong>of</strong> the<br />
components (North, South or Z (Vertical)), which are essential to run the program. Though, assum<strong>in</strong>g<br />
a couple <strong>of</strong> <strong>in</strong>puts, they were tried to implement and convert to the specific file <strong>in</strong>put for Shake2000<br />
but it also didn’t work.<br />
As a conclusion, all <strong>of</strong> the three used earthquake scenarios are chosen from the s<strong>of</strong>tware’s own database<br />
(Table 5-5). One <strong>of</strong> these, correspond<strong>in</strong>g to the Bihar-Nepal 1934 earthquake, with a magnitude<br />
<strong>of</strong> M=8 and a 10 km epicentral distance, was proposed, which can be considered as the worst scenario<br />
for the Valley. A more plausible scenario was considered to be the same magnitude but with a 50 km<br />
distance. As a result, MAE with a Magnitude <strong>of</strong> 8 and distance <strong>of</strong> 48 km was chosen for thewrost scenario.<br />
Another one was with a magnitude <strong>of</strong> 7, at some 10-15 km us<strong>in</strong>g this <strong>in</strong>formation <strong>in</strong>ternet and<br />
the s<strong>of</strong>tware’s database was <strong>in</strong>vestigated. The second scenario is LA with 7.1 magnitude and 17.5 km.<br />
The third one is the Northridge 6.7 magnitude and 6.4 km distance.<br />
Table 5-4 shows the <strong>in</strong>itially used strong ground motions that were obta<strong>in</strong>ed from onl<strong>in</strong>e strong<br />
ground motion database; PEER. The study for this project was supported <strong>in</strong> part by the Pacific Earthquake<br />
Eng<strong>in</strong>eer<strong>in</strong>g Research (PEER) Center through the Earthquake Eng<strong>in</strong>eer<strong>in</strong>g Research Centres<br />
Program <strong>of</strong> the National Science Foundation. The PEER Strong Motion Database conta<strong>in</strong>s 1557 records<br />
from 143 earthquakes from high seismicity areas, processed by Dr. Walt Silva <strong>of</strong> Pacific Eng<strong>in</strong>eer<strong>in</strong>g<br />
us<strong>in</strong>g publicly available data from federal, state, and private contributors <strong>of</strong> strong motion data<br />
(Silva 2000). With these databases hav<strong>in</strong>g the ASCII (American Standard Code for <strong>in</strong>formation <strong>in</strong>terchange;<br />
a seven bit code represent<strong>in</strong>g a character set <strong>of</strong> modern written English) format have been implemented<br />
successfully to Shake2000. One <strong>of</strong> the good opportunities <strong>of</strong> this s<strong>of</strong>tware is the option that<br />
allows you to <strong>in</strong>put the strong ground motion file from other sources. To use the files, one has to use<br />
the converter option with<strong>in</strong> the s<strong>of</strong>tware, which makes it readable for Shake2000.<br />
Earthquake Name (Strong<br />
Ground Motion File Name)<br />
Magnitude Distance Time<br />
62<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
Loma Prieta M=6.9 28.2 km (distance closest to<br />
fault rupture)<br />
1989/10/18 00:05<br />
Kocaeli, Turkey 1999/08/17 M=7.4 197.6 km (Hypocentral) 1999/08/17<br />
Kobe M=6.9 157.2 km (distance closest to<br />
fault rupture)<br />
1995/01/16 20:46<br />
Coal<strong>in</strong>ga Thrust Fault Ms=6.5 25.5 km 1983/05/02 23:42<br />
Table 5-4 Strong ground motion obta<strong>in</strong>ed from the PEER Strong Motion database (Silva 2000).<br />
Other sources <strong>of</strong> strong ground motion files are also analysed but reach<strong>in</strong>g the data was hard or the<br />
catalogue did not cover the area related to the study area. Some <strong>of</strong> the databases that were <strong>in</strong>vestigated<br />
are:<br />
• ANSS (Advanced National <strong>Seismic</strong> System) (ANSS 1990)<br />
• (http://quake.geo.berkeley.edu/anss/cnss-detail.html#description)<br />
• IRIS SeismoQuery (Incorporated Research Institutions for Seismology)<br />
(http://www.iris.wash<strong>in</strong>gton.edu/SeismiQuery/<strong>in</strong>dex.html)(IRIS 2003)<br />
• MCEER (Multidiscipl<strong>in</strong>ary Center for Earthquake Eng<strong>in</strong>eer<strong>in</strong>g Research) (MCEER 2004)<br />
(http://mceer.buffalo.edu/l<strong>in</strong>ks/agrams.asp#top)<br />
• CISN (California Integrated <strong>Seismic</strong> Network) (CISN/Tr<strong>in</strong>et 2004)<br />
(http://doc<strong>in</strong>et3.consrv.ca.gov/csmip/cisn-edc/default.htm)<br />
• NGDC (National Geophysical Data Center) (NGDC 2002)<br />
(http://www.ngdc.noaa.gov/seg/hazard/strong.html)<br />
In the ANSS database the earthquake catalogue was cover<strong>in</strong>g Ch<strong>in</strong>a, India, Pakistan, Bhutan and Nepal.<br />
The database was from 1964 to 2002; it gave an idea for the general magnitudes for that region<br />
which ranges from 6.1 to 7.5. From IRIS database it was not possible to obta<strong>in</strong> data, because you<br />
needed to know exactly the network, station id, and channel number <strong>in</strong> order to make a query. They<br />
did not have data for Nepal or India but some 10 stations from Ch<strong>in</strong>a. MCEER has a web site to guide<br />
for other sources <strong>of</strong> databases. CISN is a comb<strong>in</strong>ed database for eng<strong>in</strong>eer<strong>in</strong>g purposes, such as the<br />
strong motion that could be felt on a build<strong>in</strong>g. This <strong>in</strong>formation is more for earthquake resistant design<br />
issues. NGDC ma<strong>in</strong>ta<strong>in</strong> an earthquake strong motion archive <strong>of</strong> over 15,000 digitised and processed<br />
accelerograph records. This web site is produced by NOAA (National Oceanic and Atmospheric Adm<strong>in</strong>istration)(NGDC<br />
2002).<br />
Another source <strong>of</strong> earthquakes was also obta<strong>in</strong>ed, the Uttarkashi and Chamoli from the northern India.<br />
In 29 March 1999 - Chamoli (Uttaranchal), India, a Mw 6.6 with the epicentral distance 9.8 km has<br />
happened. And Uttarkashi had Mw: 6.8 with a 10.5 km on 21st October 1991. The strong ground motions<br />
obta<strong>in</strong>ed could not be converted <strong>in</strong> order to use them <strong>in</strong> the s<strong>of</strong>tware: Shake2000.<br />
As mentioned before, it was possible to <strong>in</strong>put the PEER strong motion files <strong>in</strong>to Shake2000; this has<br />
been done for the Loma Prieta and Kocaeli earthquakes and used for the first trials <strong>in</strong> the analysis. But<br />
for the Kathmandu Valley the proposed worst scenarios were not compatible with the PEER list obta<strong>in</strong>ed<br />
from the web sites. So the earthquake database that is with<strong>in</strong> the s<strong>of</strong>tware was queried <strong>in</strong> order<br />
to f<strong>in</strong>d a similar characteristics earthquake. The <strong>in</strong>put motions with<strong>in</strong> the database are more than 2500.<br />
The three earthquakes selected are shown <strong>in</strong> Table 5-5. The first two are synthetically generated files<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 63
and the third one is from real records. Synthetically (theoretically) generated files are based on a series<br />
<strong>of</strong> mathematical assumptions. All <strong>of</strong> the considered three scenarios have the epicentre very close to the<br />
location <strong>of</strong> the city.<br />
Name <strong>of</strong> the earthquake Magnitude Distance<br />
Mae Center RR 2B Synthetic 8 48 km (hypocentral distance)<br />
Los Angeles Simulated 7.1 17.5 km (epicentral)<br />
SAC Steel Northridge 1994 6.7 6.4 km (epicentral)<br />
Table 5-5 The selected 3 scenario earthquakes form the Shake2000 strong motion database.<br />
These assumptions are basically related to source parameters, such as slip, rupture velocity and slip<br />
velocity function. Us<strong>in</strong>g these parameters and the particular geometry with elastic or <strong>in</strong>elastic earth<br />
results <strong>in</strong> theoretical amplitudes versus time <strong>of</strong> arrival times for the seismic waves. The travel time<br />
curves could be def<strong>in</strong>ed from the seismograms recorded from an earthquake. These curves show the<br />
time and the signal characteristics. Us<strong>in</strong>g this <strong>in</strong>formation and special formulas the magnitude and the<br />
location <strong>of</strong> the earthquake can be calculated. In pr<strong>in</strong>ciple this procedure is <strong>in</strong>verted <strong>in</strong> the generation <strong>of</strong><br />
synthetic seismograms. The seismogram records <strong>of</strong> the three selected earthquakes can be found <strong>in</strong> the<br />
appendix <strong>of</strong> the thesis.<br />
After acquir<strong>in</strong>g the <strong>in</strong>put parameters for 14 boreholes, the process <strong>of</strong> ground response analysis was<br />
done <strong>in</strong> Shake 2000. The <strong>in</strong>formation for the 14 boreholes was implemented <strong>in</strong>to the database <strong>of</strong><br />
Shake2000. The first approach for the boreholes was to analyse the PGA’s (Peak Ground Acceleration).<br />
So the program had been used to run the 1D l<strong>in</strong>ear ground response analysis and the result <strong>of</strong> the<br />
analysis were ma<strong>in</strong>ly focused on the PGA values. The response spectrum and other analysis were also<br />
done for the selected boreholes from the database. This will be discussed <strong>in</strong> later parts <strong>of</strong> this thesis.<br />
Model 2: Selection <strong>of</strong> generalized pr<strong>of</strong>ile data<br />
With the same procedure <strong>of</strong> model 1, also model 2 was calculated. The basic difference between the<br />
models is the <strong>in</strong>put <strong>of</strong> 14 po<strong>in</strong>ts <strong>in</strong>stead <strong>of</strong> the actual boreholes. These 14 po<strong>in</strong>ts were hav<strong>in</strong>g the same<br />
coord<strong>in</strong>ates <strong>of</strong> the actual boreholes <strong>in</strong> the city <strong>of</strong> Lalitpur, but the soil pr<strong>of</strong>ile used the generalized pr<strong>of</strong>ile<br />
generated by Piya, (2004). S<strong>in</strong>ce the simplified soil pr<strong>of</strong>ile had 4 layers, these po<strong>in</strong>ts also had the<br />
same 4 layers.<br />
Unit weight, and shear wave velocity have been <strong>in</strong>terpreted us<strong>in</strong>g the former assumptions. The only<br />
variable <strong>in</strong> this case was the thickness for each layer. The thickness <strong>of</strong> the 4-layer model was read us<strong>in</strong>g<br />
the maps <strong>of</strong> Piya, (2004) us<strong>in</strong>g the ILWIS table calculation programme. The maps provided the<br />
thickness <strong>of</strong> the pre-lake deposits, the lake deposits and the materials overlay<strong>in</strong>g the lake sediments.<br />
Here, the soil part is basically divided <strong>in</strong>to three types: top, bottom and lake. From the bedrock till the<br />
surface the soil types are: Rock, Gravel, Clay and Sand/Silt. Us<strong>in</strong>g the <strong>in</strong>formation <strong>in</strong> the Table 5-6,<br />
the <strong>in</strong>put values were <strong>in</strong>tegrated <strong>in</strong>to Shake2000. Damp<strong>in</strong>g was kept at 5% just like <strong>in</strong> the former<br />
analysis. The shear wave velocities are aga<strong>in</strong> used <strong>in</strong> two sets as <strong>in</strong> Table 5-3. The <strong>in</strong>put motions are<br />
also the same three earthquakes, as chosen before.<br />
64<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
Layer<br />
Thickness (example<br />
values)<br />
Unit Weight<br />
Shear wave<br />
Velocity<br />
(Feet) Meters (Kcf) KN/m3 (Fps) M/s<br />
Damp<strong>in</strong>g<br />
(decimal)<br />
Recent alluvial: 1 82 24.9 0.11 17.5 1476 450 0.05<br />
Lake deposits: 2 360 109.7 0.1 16 1968 600 0.05<br />
Pre-lake deposits: 3 580 176.7 0.13 20 5577 1700 0.05<br />
Bedrock: 4 - 0.14 22 9842 3000 0.05<br />
Table 5-6 Generalized soil pr<strong>of</strong>ile values that are used <strong>in</strong> the soil site analysis.<br />
Comparison <strong>of</strong> the two models (Model 1 & 2)<br />
Results <strong>of</strong> the Peak Ground Acceleration Values<br />
The results <strong>of</strong> the analysis provided <strong>in</strong>formation on the sensitivity <strong>of</strong> the follow<strong>in</strong>g four aspects:<br />
1. Shear wave velocity (Set 1 and 2: m<strong>in</strong>imum and maximum values)<br />
2. Earthquakes (3 Scenarios)<br />
3. Thickness (Deep and Shallow boreholes, generalized soil thickness)<br />
4. <strong>Soil</strong> Pr<strong>of</strong>ile (Many layers versus 4 layers)<br />
All these aspects are assessed and compared us<strong>in</strong>g the output Peak Ground Acceleration values. It was<br />
more convenient to use PGA outcome then the others (response spectrum and amplification spectrum<br />
graphs) s<strong>in</strong>ce it gives a s<strong>in</strong>gle value. Such as response spectrum, amplification graph is also hard to<br />
compare once you have many data and time constra<strong>in</strong>ts. All these four aspects can be divided <strong>in</strong>to<br />
smaller sections and compared between each other. But the general research question that should be<br />
answered from these graphs is the difference <strong>in</strong> result<strong>in</strong>g acceleration between the actual and the generalized<br />
soil pr<strong>of</strong>iles. This could be answered by plott<strong>in</strong>g the PGA values <strong>of</strong> the actual boreholes and<br />
the correspond<strong>in</strong>g po<strong>in</strong>ts read from the generalized soil pr<strong>of</strong>ile. Such a graph, <strong>in</strong>clud<strong>in</strong>g the other parameters<br />
such as shear wave velocity and earthquake scenarios, would be relatively complex so that it<br />
has been divided <strong>in</strong>to smaller charts (Figure 5-3). In Figure 5-3, the first earthquake scenario has<br />
smaller PGA values then the other two. This is a little contrary to what one would expect, s<strong>in</strong>ce the<br />
magnitude is higher than the other two (M=8). But the other two earthquakes occur very close to the<br />
Lalitpur area. The second earthquake is 17,5 km and the third one is 6.4 km, which would <strong>in</strong>fluence<br />
the accelerations more, with the earthquakes that are chosen. (Second scenario; M=7.1 and Third scenario;<br />
M=6.7)<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 65
Scenario 1 Scenario 2 Scenario 3<br />
PGA (g)<br />
1.6<br />
1.4<br />
1.2<br />
1<br />
0.8<br />
0.6<br />
0.4<br />
0.2<br />
0<br />
B25 BHD3 AG 68 B23 P29 DMG13 P37<br />
Borehole ID<br />
A<br />
Series1 Series2 Series3<br />
PGA (g)<br />
1.6<br />
1.4<br />
1.2<br />
1<br />
0.8<br />
0.6<br />
0.4<br />
0.2<br />
0<br />
B25 AG 68 P29 P37<br />
Borehole ID<br />
B<br />
Figure 5-3 The deep boreholes correspondent PGA values for the shear wave velocity set 1 (A: m<strong>in</strong>imum<br />
Vs values) and 2 (B: maximum Vs values).<br />
From Figure 4-3 several th<strong>in</strong>gs can be concluded for the deep boreholes and their PGA results. First,<br />
the two graphs show different PGA for different shear wave velocities (Set 1 and 2). When we compare<br />
the PGA value range for the two, it is easy to see that the second set which has higher shear wave<br />
velocity values than the first set gave higher PGA values for all boreholes. So an <strong>in</strong>crease <strong>of</strong> shear<br />
wave velocity gives a higher Peak Ground Acceleration, which is unexpected. Second, the second scenario<br />
earthquake has almost always higher PGA values then the other two scenarios. The lowest PGA<br />
values are produced from the worst scenario earthquake, which is also unexpected. But this consequence<br />
is very related to Shake2000 limitations and the use <strong>of</strong> the synthetic earthquake that has been<br />
chosen. This will be further discussed <strong>in</strong> Chapter 7.<br />
The general acceleration differences between the actual boreholes and the generalized soil pr<strong>of</strong>ile<br />
po<strong>in</strong>ts are basically depend on the:<br />
• Depth <strong>of</strong> bedrock level<br />
66<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
• <strong>Soil</strong> thickness.<br />
The two mentioned parameters show similarity when the po<strong>in</strong>t <strong>of</strong> view is the shear wave velocity sets.<br />
The correlation between the PGA values for actual boreholes and the simplified 4-layer po<strong>in</strong>ts are observed<br />
to be good <strong>in</strong> the deep boreholes/po<strong>in</strong>ts. The expected good correlation refers to the close range<br />
<strong>of</strong> peak acceleration values for both the actual boreholes and the generalized pr<strong>of</strong>ile po<strong>in</strong>ts. For example,<br />
the range <strong>of</strong> acceleration values with the same shear wave velocity set (1) for P37 borehole/po<strong>in</strong>t<br />
is from 0.2 to 0.4 g. On the other hand for shallow boreholes/po<strong>in</strong>ts the difference range could go as<br />
high as up to 2.75 g. The probable reason for this is; high values are produced by the shallow boreholes,<br />
which are very close to the surface (Even 1.45 m). The pr<strong>of</strong>ile then uses the bedrock as close as<br />
this value, which is not a realistic case. In reality the area has thick unconsolidated materials reach<strong>in</strong>g<br />
up to 500 meters. The shallow borehole does not end at the level <strong>of</strong> the bedrock. Because, <strong>of</strong> this the<br />
results from the shallow boreholes were excluded from the analysis. The correlation between the<br />
PGA values from the deep boreholes correlation and the generalized soil pr<strong>of</strong>ile po<strong>in</strong>ts is more dependable<br />
then for the shallow boreholes. But, this also changes when the shear wave velocity changes.<br />
Likewise, for lower values <strong>of</strong> shear wave velocity the correlation <strong>of</strong> the actual boreholes and the po<strong>in</strong>ts<br />
are much better then the second set with higher values. So, we expect the actual shear wave velocity<br />
values to be more close to the m<strong>in</strong>imum values that were used <strong>in</strong> the analysis. But this should be tested<br />
with many other tests, us<strong>in</strong>g several shear wave velocity sets.<br />
Overall Results <strong>in</strong>dicate that:<br />
• Depth <strong>of</strong> bedrock level and soil thickness plays an important role <strong>in</strong> the correlation <strong>of</strong> the actual<br />
boreholes and the generalized soil pr<strong>of</strong>ile po<strong>in</strong>ts.<br />
• Los Angeles simulated earthquake with a magnitude <strong>of</strong> 7.1 and distance 17.5 km produced the<br />
highest acceleration values for both the actual boreholes and the generalized pr<strong>of</strong>ile po<strong>in</strong>ts <strong>in</strong><br />
Lalitpur.<br />
• The extreme values <strong>of</strong> PGA could be caused by wrong selection <strong>of</strong> soil depths and shear wave<br />
velocities for the soil pr<strong>of</strong>iles. Assign<strong>in</strong>g very thick or th<strong>in</strong> levels to a specific soil type also<br />
affects the output values. For <strong>in</strong>stance, very thick Clay sediment would result <strong>in</strong> high acceleration<br />
values, but a th<strong>in</strong> Clay layer would not affect that much with<strong>in</strong> the pr<strong>of</strong>ile.<br />
• The shallow boreholes should not be used if the layers till bedrock are not known. They create<br />
unrealistic values.<br />
• In general, the assumption that higher acceleration values are obta<strong>in</strong>ed if the soil thickness <strong>in</strong>creases<br />
and if the shear wave velocity decreases was not supported by the results.<br />
Results <strong>of</strong> the <strong>Response</strong> Spectra <strong>Analysis</strong><br />
Apart from the PGA value analysis, response spectra curves were also generated for the selected boreholes.<br />
The selection was based on the acceleration responses with lowest, mean and highest values for<br />
the 3 scenario earthquakes and two sets <strong>of</strong> shear wave velocities (m<strong>in</strong>imum and maximum values). For<br />
the highest values borehole PR16 was taken, Borehole B25 for the medium values, and B23 for the<br />
lowest values. Figures 5-4, 5-5 and 5-6 shows the response spectra <strong>of</strong> the actual boreholes and the correspond<strong>in</strong>g<br />
generalized pr<strong>of</strong>ile po<strong>in</strong>ts. On the left side <strong>of</strong> the Figures, the response spectra are given<br />
for the generalized pr<strong>of</strong>iles and on the right side the ones for the actual boreholes. For B25 the shear<br />
wave velocity set 1 was used, and for PR16 and B23 the shear wave velocity set 2 was used (Table 5-<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 67
7). Though the magnitude is great and the hypocentral distance is very close, a value over 2.35 g is not<br />
a reliable value theoretically.<br />
Po<strong>in</strong>t ID<br />
Thickness <strong>of</strong> the<br />
post-lake deposits<br />
(m)<br />
Thickness <strong>of</strong> the<br />
lake deposits (m)<br />
Thickness <strong>of</strong> the prelake<br />
deposits (m)<br />
Total thickness<br />
<strong>of</strong> the<br />
soil site (m)<br />
B25 (Po<strong>in</strong>t ID: 8) 3 62 7 92<br />
PR 16 (Po<strong>in</strong>t ID: 14) 3 91 79 202<br />
B23 (Po<strong>in</strong>t ID: 43) 30 141 95 318<br />
Table 5-7 The chosen po<strong>in</strong>ts (they correspond to actual boreholes) from the generalized 4 layer pr<strong>of</strong>ile.<br />
For borehole PR16 us<strong>in</strong>g the scenario earthquake Los Angeles, with Magnitude: 6.2 and distance 15<br />
km the maximum acceleration <strong>of</strong> the acceleration record is 0.32 g. This earthquake is used because <strong>of</strong><br />
the results obta<strong>in</strong>ed from the sensitivity analysis and the extreme values obta<strong>in</strong>ed before. From the upcom<strong>in</strong>g<br />
analysis it is found out that the scenario earthquakes should not exceed the acceleration maximum<br />
<strong>of</strong> 0.45 g for the Shake2000 s<strong>of</strong>tware. For PR 16 the bedrock level from the generalized soil pr<strong>of</strong>ile<br />
was also used. The last layer conta<strong>in</strong>ed the weathered limestone so the bedrock was already shown<br />
when the actual borehole pr<strong>of</strong>ile was used. There was no need to assign a soil layer type for the difference<br />
between the given bedrock level (from generalized pr<strong>of</strong>ile) and the actual log.<br />
The various peaks at different frequencies <strong>of</strong> the response curve match with the height <strong>of</strong> build<strong>in</strong>gs and<br />
may cause resonance if they co<strong>in</strong>cide with the natural frequency <strong>of</strong> the build<strong>in</strong>gs. So it seems high<br />
build<strong>in</strong>gs would suffer much more damage then the low ones <strong>in</strong> Lalitpur city. Look<strong>in</strong>g at the other<br />
curves, for example for po<strong>in</strong>t 43 (B23) it suggests reliable values and gives the peak acceleration values<br />
0.6 and 1.5. Here also high build<strong>in</strong>gs are considered to be very susceptible to damage. As the frequencies<br />
gets low the storey number <strong>in</strong>creases. Aga<strong>in</strong> the generalized and the actual borehole response<br />
spectra do not fit well. The response spectrum from the actual borehole shows a high peak <strong>in</strong> the frequency<br />
<strong>of</strong> 1 Hertz (related to 10 storey build<strong>in</strong>gs). The last curves <strong>in</strong> Figure 5.6 are for the borehole<br />
with the lowest acceleration values. At first sight, the two curves fit <strong>in</strong> pattern, but <strong>in</strong> detail they are<br />
not very good l<strong>in</strong>ked. The generalized pr<strong>of</strong>ile shows a high peak for the frequency value <strong>of</strong> 4.9 Hertz.<br />
Here, four storey build<strong>in</strong>gs are more susceptible to the damage. And, the real spectrum shows a peak at<br />
frequency <strong>of</strong> 1 Hertz with an acceleration <strong>of</strong> 2.4 g creat<strong>in</strong>g damage to 10 storey build<strong>in</strong>gs more then<br />
the others. On the whole, B23 showed reliable values for both <strong>of</strong> the curves. B25 showed a bit less<br />
reliability for the generalized pr<strong>of</strong>ile but it’s the actual borehole showed trustable spectrum.<br />
General results obta<strong>in</strong>ed from the response spectrum curves can be summarized as follows:<br />
• Either generalized pr<strong>of</strong>ile or real <strong>in</strong>vestigations for the same po<strong>in</strong>t could differ significantly.<br />
• The first two scenario earthquakes did reach high values but the third one did not reach that<br />
much (Northridge). This relation will be discussed <strong>in</strong> further sections.<br />
• The Peak Ground Acceleration values, which depend on the accelerations time history, reflect<br />
more sensible values as compared to the response spectrum. The highest peaks did not reach<br />
very extreme values <strong>in</strong> the acceleration time histories.<br />
68<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
PR 16 - <strong>Analysis</strong> No. 1 - Pr<strong>of</strong>ile No. 2 - Layer 1<br />
4<br />
Spectral Acceleration (g)<br />
3<br />
2<br />
1<br />
0<br />
0.1 1 10 100<br />
Frequency (Hz)<br />
Po<strong>in</strong>t 14 (PR16)<br />
<strong>Soil</strong> Pr<strong>of</strong>ile No. 1 - <strong>Analysis</strong> No. 1 - Pr<strong>of</strong>ile No. 1 - Layer 3<br />
1.5<br />
Spectral Acceleration (g)<br />
1.0<br />
0.5<br />
0.0<br />
0.1 1 10 100<br />
Frequency (Hz)<br />
PR16 Borehole<br />
Figure 5-4 The response spectrum curves for three critical boreholes and correspondent po<strong>in</strong>ts for the<br />
earthquake scenarios (For PR 16 LA M=6.2).<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 69
B 23 - <strong>Analysis</strong> No. 1 - Pr<strong>of</strong>ile No. 3 - Layer 1<br />
2.5<br />
2.0<br />
Spectral Acceleration (g)<br />
1.5<br />
1.0<br />
0.5<br />
0.0<br />
0.1 1 10 100<br />
Frequency (Hz)<br />
Po<strong>in</strong>t 43 (B23)<br />
VS SET 2 - <strong>Analysis</strong> No. 1 - Pr<strong>of</strong>ile No. 1 - Layer 1<br />
3.0<br />
2.5<br />
Spectral Acceleration (g)<br />
2.0<br />
1.5<br />
1.0<br />
0.5<br />
0.0<br />
0.1 1 10 100<br />
Frequency (Hz)<br />
B23 Borehole<br />
Figure 5-5 The response spectrum curves for three critical boreholes and correspondent po<strong>in</strong>ts for the<br />
earthquake scenarios (M=8, R=48km for B23).<br />
70<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
B 25 - <strong>Analysis</strong> No. 1 - Pr<strong>of</strong>ile No. 3 - Layer 1<br />
5<br />
4<br />
Spectral Acceleration (g)<br />
3<br />
2<br />
1<br />
0<br />
0.1 1 10 100<br />
Frequency (Hz)<br />
Po<strong>in</strong>t 8 (B25)<br />
B 25 - <strong>Analysis</strong> No. 1 - Pr<strong>of</strong>ile No. 3 - Layer 1<br />
2.5<br />
2.0<br />
Spectral Acceleration (g)<br />
1.5<br />
1.0<br />
0.5<br />
0.0<br />
0.1 1 10 100<br />
Frequency (Hz)<br />
B25 Borehole<br />
Figure 5-6 The response spectrum curves for three critical boreholes and correspondent po<strong>in</strong>ts for the<br />
earthquake scenarios (M=8, R=48km for B25).<br />
For the examples shown above, the bedrock level was considered to be right after the last soil layer <strong>in</strong><br />
the borehole pr<strong>of</strong>ile. In this example, the borehole: for P37 the bedrock level was read from the generalized<br />
pr<strong>of</strong>ile. P37 has the follow<strong>in</strong>g stratigraphy and altitudes (<strong>in</strong> meters)(Figure 5-7). In generalized<br />
pr<strong>of</strong>ile the depth was 419 feet (127.71 m) and the actual borehole was till 370 feet (112.7 m). The difference<br />
between the levels was 160.7 feet. This difference was considered to be the Gravely layer till<br />
bedrock level <strong>of</strong> the generalized pr<strong>of</strong>ile. The calculations for this borehole were done us<strong>in</strong>g this layer<br />
also. The aim was to see if the two layers match up or not <strong>in</strong> the response analysis. The earthquake<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 71
used is Los Angeles, Magnitude: 6.2 distance 15 km and the maximum acceleration <strong>of</strong> the acceleration<br />
record is 0.32 g like PR16 borehole.<br />
Look<strong>in</strong>g at the Figure 5-8 and 5-9, the range <strong>of</strong> values for both <strong>of</strong> the graphs response and amplification<br />
spectrum, was close. But, <strong>in</strong> detail the peaks and frequencies were different. It appears to be they<br />
would suggest very different natural frequencies for the same environment. This could be taken as one<br />
or other is not giv<strong>in</strong>g the reality close enough. S<strong>in</strong>ce, borehole log depends on the actual data, it shows<br />
the reality. Nevertheless, this example shows that simplify<strong>in</strong>g the subsurface geology will not show<br />
the ground response accurate enough.<br />
Figure 5-7 The stratigraphic section <strong>of</strong> P37 borehole log.<br />
72<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
<strong>Soil</strong> Pr<strong>of</strong>ile No. 1 - <strong>Analysis</strong> No. 1 - Pr<strong>of</strong>ile No. 1 - Layer 1<br />
2.0<br />
Spectral Acceleration (g)<br />
1.5<br />
1.0<br />
0.5<br />
0.0<br />
0.1 1 10 100<br />
Frequency (Hz)<br />
A<br />
SPT 25 - <strong>Analysis</strong> No. 1 - Pr<strong>of</strong>ile No. 1 - Layer 1<br />
2.0<br />
Spectral Acceleration (g)<br />
1.5<br />
1.0<br />
0.5<br />
0.0<br />
0.1 1 10 100<br />
Frequency (Hz)<br />
B<br />
Figure 5-8 The Figure is show<strong>in</strong>g the actual borehole (ID: P37) and the po<strong>in</strong>t read from the generalized<br />
soil pr<strong>of</strong>ile. A and C belongs to the actual borehole. The A and B are the response spectra for the chosen<br />
scenario earthquake (Los Angeles M: 6.2; D: 15 km).<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 73
<strong>Soil</strong> Pr<strong>of</strong>ile No. 1 - <strong>Analysis</strong> No. 1 - Pr<strong>of</strong>ile No. 1<br />
6<br />
5<br />
Amplification Ratio<br />
4<br />
3<br />
2<br />
1<br />
0<br />
0 5 10 15 20 25<br />
Frequency (Hz)<br />
C<br />
SPT 25 - <strong>Analysis</strong> No. 1 - Pr<strong>of</strong>ile No. 1<br />
8<br />
6<br />
Amplification Ratio<br />
4<br />
2<br />
0<br />
0 5 10 15 20 25<br />
Frequency (Hz)<br />
D<br />
Figure 5-9 The Figure is show<strong>in</strong>g the actual borehole (ID: P37) and the po<strong>in</strong>t read from the generalized<br />
soil pr<strong>of</strong>ile. A and C belongs to the actual borehole, the others C and D are from the generalized pr<strong>of</strong>ile.<br />
The C and D are the amplification spectrums for chosen scenario earthquake (Los Angeles M: 6.2; D: 15<br />
km).<br />
5.1.2 Methodology 2: Generat<strong>in</strong>g acceleration maps<br />
In the second methodology, a generalized subsurface layer model was used (Piya, 2004). Figure 5-10,<br />
shows a flowchart <strong>of</strong> the followed method. This layer model (consist<strong>in</strong>g <strong>of</strong> bedrock, pre-lake deposits,<br />
lake deposits, and recent sediments) was based on 185 boreholes that are collected from the Kathmandu<br />
Valley, and it gives for each po<strong>in</strong>t an idea on the soil types and soil thickness. Shear wave velocity<br />
and unit weight parameters that are essential <strong>in</strong> the soil site response analysis should be l<strong>in</strong>ked to<br />
these layers. The values that are used <strong>in</strong> the analysis are shown <strong>in</strong> Table 5-8.<br />
74<br />
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GROUND RESPONSE MODELLING<br />
Methodology 2<br />
Input Parameters<br />
60 po<strong>in</strong>ts with generalized thickness data and generalized 4<br />
layer soil pr<strong>of</strong>ile.<br />
Input Motion<br />
Mae Center RR 2B Synthetic<br />
Magnitude: 8<br />
Hypocentral Distance: 48 km<br />
Output<br />
•PGA Map <strong>of</strong> the study area.<br />
•Modified Mercalli Intensity Map (us<strong>in</strong>g Trifunac and<br />
Brandy 1975 formula)<br />
•Map show<strong>in</strong>g the natural frequency <strong>of</strong><br />
build<strong>in</strong>gs that would create resonance<br />
with the <strong>in</strong>put motion frequencies.<br />
•Different period maps for selected<br />
shear wave velocities.<br />
Figure 5-10 Flowchart <strong>of</strong> the method 2.<br />
<strong>Soil</strong> Type<br />
Unit weight<br />
KN/m3<br />
kcf<br />
Shear Wave Velocity<br />
(1 st set) m/s<br />
f/s<br />
Shear Wave Velocity<br />
(2 nd set) m/s<br />
Sandy/Silty 17.5 0.11 550 1804 450 1476<br />
Clay 16 0.10 300 984 600 1968<br />
Gravel 20 0.13 1000 3281 1700 5577<br />
Rock 22 0.14 3000 9842 3000 9842<br />
Table 5-8 Four-layer generalized soil pr<strong>of</strong>iles attributes that are used <strong>in</strong> the response calculation <strong>in</strong><br />
Shake2000.<br />
Ft/s<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 75
The soil pr<strong>of</strong>ile is divided <strong>in</strong>to four layers. The first layer from the surface is ma<strong>in</strong>ly consist<strong>in</strong>g <strong>of</strong><br />
Sandy and Silty sediments. The second layer consists <strong>of</strong> Clay sediments, which were formed <strong>in</strong> the<br />
lake that existed <strong>in</strong> the valley up to 29000 B.P. The third layer ma<strong>in</strong>ly consists <strong>of</strong> Gravel. Lastly, the<br />
fourth layer is the bedrock ma<strong>in</strong>ly consist<strong>in</strong>g <strong>of</strong> limestone, Sandstone, Slates and Phyllites. After def<strong>in</strong><strong>in</strong>g<br />
the sediment types it is possible to <strong>in</strong>terpret the geotechnical parameters used <strong>in</strong> the analysis.<br />
The unit weight and shear wave values are based on the general values which were derived from different<br />
<strong>in</strong>formation sources (Koloski, Schwarz et al. 1989; Whitlow 1995; Cur 1996) and discussions<br />
(S. Slob and R. Hack, personal communication). For damp<strong>in</strong>g a percentage <strong>of</strong> 5 has been accepted as a<br />
default value. Every material type had to be also def<strong>in</strong>ed us<strong>in</strong>g the dynamic material properties (Figure<br />
5-11). For damp<strong>in</strong>g <strong>of</strong> Sand, Clay, Gravel and Rock, there was only one option, which was based on<br />
the various studies, mentioned <strong>in</strong> Table 5-9. For the Gravel layer a choice had to be made between the<br />
Gravely soils and Gravel options. Gravely soils found to be more representative for the region. And<br />
for the modulus reduction curves, Clay options were depend<strong>in</strong>g on the plasticity <strong>in</strong>dex <strong>of</strong> Clays .The<br />
plasticity <strong>of</strong> f<strong>in</strong>e soils has importance <strong>in</strong> the eng<strong>in</strong>eer<strong>in</strong>g purposes where it def<strong>in</strong>es the shear strength<br />
and compressibility. And, the plastic states <strong>of</strong> soils are given by the plasticity <strong>in</strong>dex. The options <strong>in</strong>cluded<br />
0, 10, 20, 40 and above 80. In order to make a sensible assumption Clay 20 was chosen. For<br />
Sand, three types were def<strong>in</strong>ed Sand 1, 2 and 3 for reduction modulus curve option. Sand 2 was chosen.<br />
And for Gravel, Gravel average was used. The shear stra<strong>in</strong> and modulus reduction curve/ damp<strong>in</strong>g<br />
ratio relations can be observed from Figure 5-11. The first graph shows that the shear modulus types<br />
are gradually decreas<strong>in</strong>g while the shear stra<strong>in</strong>s <strong>in</strong>creases. After 1% <strong>of</strong> the shear stra<strong>in</strong>, only Clay<br />
could cont<strong>in</strong>ue to decrease till 10 %. Clay can undertake more stra<strong>in</strong>s then the other materials <strong>in</strong> the<br />
chosen pr<strong>of</strong>ile. In the damp<strong>in</strong>g curve, while the damp<strong>in</strong>g percentage <strong>in</strong>creases the shear stra<strong>in</strong>s also<br />
<strong>in</strong>crease. For values more then the 1 % shear stra<strong>in</strong> Clay and Sand has shear stra<strong>in</strong>s till 10% correspond<strong>in</strong>g<br />
up to 30% damp<strong>in</strong>g ratios.<br />
Material Type Modulus Name (Shake 2000) Damp<strong>in</strong>g<br />
Sandy/Silty G/Gmax - S2 (SAND CP=1-3 KSC) 3/11 1988 Damp<strong>in</strong>g for SAND, February<br />
1971<br />
Clay G/Gmax - C3 (CLAY PI =20-40, Sun et al. 198) Damp<strong>in</strong>g for CLAY May 24 -<br />
1972<br />
Gravel G/Gmax - GRAVEL, Average (Seed et al. 1986) Damp<strong>in</strong>g for Gravely <strong>Soil</strong>s (Seed<br />
et al 1988)<br />
Rock G/Gmax - ROCK (Schnabel 1973) Damp<strong>in</strong>g for ROCK (Schnabel<br />
1973)<br />
Table 5-9 Dynamic material properties are shown for the four-layer generalized model.<br />
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Shear Modulus Reduction Curves<br />
Modulus Reduction (G/Gmax)<br />
1.0<br />
0.8<br />
0.6<br />
0.4<br />
Sand S2 G/Gmax - S2<br />
(SAND CP=1-3 KSC)<br />
3/11 1988<br />
Clay PI=20 G/Gmax -<br />
C3 (CLAY PI =20-40,<br />
Sun et al. 198)<br />
Gravel Avg. G/Gmax -<br />
GRAVEL, Average<br />
(Seed et al. 1986)<br />
Rock G/Gmax -<br />
ROCK (Schnabel 1973)<br />
0.2<br />
0.0<br />
0.00001 0.0001 0.001 0.01 0.1 1 10<br />
Shear Stra<strong>in</strong> (%)<br />
a.<br />
Damp<strong>in</strong>g Ratio (%)<br />
Damp<strong>in</strong>g Ratio Curves<br />
30<br />
25<br />
20<br />
15<br />
10<br />
Sand Damp<strong>in</strong>g for<br />
SAND, February 1971<br />
Clay Damp<strong>in</strong>g for<br />
CLAY May 24 - 1972<br />
Gravel Damp<strong>in</strong>g for<br />
Gravelly <strong>Soil</strong>s (Seed et<br />
al 1988)<br />
Rock Damp<strong>in</strong>g for<br />
ROCK (Schnabel 1973)<br />
5<br />
0<br />
0.00001 0.0001 0.001 0.01 0.1 1 10<br />
Shear Stra<strong>in</strong> (%)<br />
b.<br />
Figure 5-11 The dynamic material properties and their relation to the shear stra<strong>in</strong>, which are used for the<br />
four-layer soil pr<strong>of</strong>ile. (a and b)<br />
The first parameter; thickness was obta<strong>in</strong>ed from the thickness maps produced before. Three thickness<br />
maps were used which refer to the altitudes <strong>of</strong> the boundaries between the four layers. For develop<strong>in</strong>g<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 77
the <strong>in</strong>put data, all spatial calculations have been made <strong>in</strong> ILWIS. The pixel size has been changed to<br />
500 by 500 m pixels <strong>in</strong> the Lalitpur area, which gave 60 pixels for Lalitpur site. 60 pixels meant 60<br />
times runn<strong>in</strong>g Shake2000, so that the denser pixel sizes were not chosen because <strong>of</strong> the time constra<strong>in</strong>ts.<br />
In ILWIS the three thickness maps have been converted to po<strong>in</strong>t maps and then all the values<br />
for each map were collected <strong>in</strong> a table. So, each po<strong>in</strong>t had three values: thickness <strong>of</strong> the layer, which is<br />
above the lake layer (also called top <strong>of</strong> the lake), the lake layer thickness and the layer below the lake<br />
layer (also called lake bottom) (Figure 5-12). For the thickness <strong>of</strong> the fourth layer; Rock, it is considered<br />
that this layer has an <strong>in</strong>f<strong>in</strong>ite thickness <strong>in</strong> the analysis <strong>of</strong> 1D horizontal layer earthquake response<br />
analysis. Result<strong>in</strong>g thickness values were passed to the Excel files that are used to prepare the calculations.<br />
As there were now 60 different po<strong>in</strong>ts for which the Shake2000 had to be used, which took a<br />
long time, especially <strong>in</strong> prepar<strong>in</strong>g the <strong>in</strong>put files, only one scenario earthquake has been chosen. The<br />
worst scenario was applied <strong>in</strong> the calculations (M=8, R=48km; Synthetic).<br />
Top <strong>of</strong> the lake deposits<br />
Lake deposits<br />
Bottom <strong>of</strong> the lake deposits<br />
Rock Layer<br />
Figure 5-12 The illustration <strong>of</strong> the generalized subsurface geology <strong>of</strong> the Kathmandu Valley.<br />
From the analysis results <strong>in</strong> Shake 2000, 60 PGA values have been produced. From the raster map<br />
show<strong>in</strong>g 500 by 500 m pixels, a po<strong>in</strong>t map was created <strong>in</strong> order to make it easier to l<strong>in</strong>k the po<strong>in</strong>ts with<br />
the attributes. These PGA values were associated with the po<strong>in</strong>ts <strong>in</strong> the map. After convert<strong>in</strong>g to raster<br />
the PGA map had been densified and resampled. It can be seen from the PGA map produced (Figure<br />
5-13) Along with Ch<strong>in</strong>a, Myanmar, Afghanistan and Taiwan, Nepal has the highest hazard values <strong>of</strong><br />
PGA <strong>in</strong> the Asian cont<strong>in</strong>ent (Giard<strong>in</strong>i 1999). Once, the PGA value is known, it is possible to calculate<br />
the MMI (Modified Mercalli Intensity). For this the formula from Trifunac and Brandy (1975) was<br />
used:<br />
MMI =1/0.3*(LOG 10 (PGA*980)-0.014)<br />
The relation between Shake 2000 analysis and the ILWIS map creation can be seen <strong>in</strong> a summarized<br />
diagram <strong>in</strong> Figure 5-14.<br />
In the report <strong>of</strong> JICA (2001) on earthquake loss estimation for Kathmandu Valley, the Mid Nepal<br />
earthquake was correspond<strong>in</strong>g to a great magnitude earthquake (Above 8). The Kathmandu Valley<br />
Local earthquake is a local earthquake occurr<strong>in</strong>g with<strong>in</strong> the Valley. The last scenario earthquake used<br />
by JICA (2001) is the so-called North Bagmati Earthquake, which is a middle scale earthquake. These<br />
earthquake scenarios have been used by JICA (2001) to create the ground response and the <strong>in</strong>tensity<br />
78<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
estimations Figure 5-13. An earthquake occurr<strong>in</strong>g <strong>in</strong> the subduction boundary <strong>of</strong> Himalayas was calculated<br />
to give <strong>in</strong>tensity <strong>of</strong> 8 for the region. Consider<strong>in</strong>g the closeness <strong>of</strong> the source <strong>in</strong> this research, the<br />
MMI map produced is <strong>in</strong>deed <strong>in</strong> good correlation with the JICA’s <strong>in</strong>tensity map. For the Kathmandu<br />
Valley local earthquake the high <strong>in</strong>tensity is clustered on the northwest <strong>of</strong> the region. This cluster<strong>in</strong>g<br />
could also be recognized <strong>in</strong> the MMI map <strong>of</strong> this study. JICA assigned <strong>in</strong>tensity n<strong>in</strong>e for a local scenario<br />
and this scenario is basically <strong>in</strong> close relationship with the scenario chosen for Lalitpur site. The<br />
scenario <strong>of</strong> the North Bagmati earthquake also co<strong>in</strong>cides with the <strong>in</strong>tensities <strong>of</strong> this study s<strong>in</strong>ce it has<br />
shown the <strong>in</strong>tensity seven <strong>in</strong> general.<br />
Figure 5-13 The <strong>in</strong>tensity maps visualized from JICA report. (JICA, 2001) The <strong>in</strong>tensities are for the scenario<br />
earthquakes named (from left through right) respectively; Mid Nepal, Kathmandu Valley Local and<br />
North Bagmati.<br />
A further step is to create spectral acceleration maps for different frequencies for resonance zonation.<br />
Every calculation <strong>in</strong> each po<strong>in</strong>t has produced a response spectrum. The response spectrum was calculated<br />
for the surface so that it can be related to the build<strong>in</strong>gs on the surface. This <strong>in</strong>formation is important<br />
s<strong>in</strong>ce it gives the relation between the build<strong>in</strong>gs and the strong ground motion. First, for the eng<strong>in</strong>eer<strong>in</strong>g<br />
purposes, the generally used storey number should be determ<strong>in</strong>ed. The average number <strong>of</strong><br />
floors is 3 or 4 <strong>in</strong> the Lalitpur area (Guraga<strong>in</strong>, personal communication). A series <strong>of</strong> frequencies<br />
match<strong>in</strong>g this average value and other special frequencies were determ<strong>in</strong>ed. Table 5-10 shows the relations<br />
that could be used.<br />
Fundamental<br />
Frequency (Hz)<br />
Fundamental<br />
Period (sec.)<br />
N (Ingeom<strong>in</strong>as, 1999;<br />
Arnold, 1982)<br />
N (Vidal et.<br />
al.,1998)<br />
N(Day, 2001)<br />
10 0.1 1 storey 2 1<br />
5 0.2 2 4 2<br />
2 0.5 4 8 5<br />
1-0.5 1.0-0.2 10-20 20-40 10-20<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 79
Table 5-10 The relations between the fundamental frequencies and the storey numbers <strong>of</strong> the build<strong>in</strong>gs<br />
from three different sources (Vidal and Yamanaka 1998; INGEOMINAS 1999; Day 2001).<br />
From the relations mentioned <strong>in</strong> the table Day, 2001 was used. The relation was def<strong>in</strong>ed as follows;<br />
F= 10/N<br />
Here F is the fundamental frequency and N is the storey number. Us<strong>in</strong>g above formula and the determ<strong>in</strong>ed<br />
frequencies for the study area, resonance maps were produced. There are rarely 10 storey build<strong>in</strong>gs<br />
<strong>in</strong> the study area but it is <strong>in</strong>cluded for references.<br />
Frequency (Hz)<br />
5 2<br />
3 3<br />
2 5<br />
1 10<br />
N (Storey number,<br />
Day, 2001)<br />
Table 5-11 The fundamental frequencies for Lalitpur and their storey numbers.<br />
Given the frequencies, the spectral accelerations were read from the response spectra <strong>of</strong> the po<strong>in</strong>ts.<br />
Then, these values were moved to the ILWIS tables and attribute maps were created from these columns.<br />
The attribute maps F1, F2, F3 and F5 can be seen <strong>in</strong> the Figure 5-14. The graphs for frequencies<br />
1, 2, 3 and 5 have high spectral accelerations <strong>in</strong> the North West side <strong>of</strong> the area. The high values <strong>in</strong> the<br />
middle could also be seen <strong>in</strong> the frequency <strong>of</strong> 3 Hz map. The highest spectral acceleration was obta<strong>in</strong>ed<br />
<strong>in</strong> the frequency map <strong>of</strong> 1 Hz with a value <strong>of</strong> 4.9 g. The high values <strong>of</strong> the spectral accelerations<br />
will be discussed <strong>in</strong> further sections. For 3Hz-frequency map, there are three clusters <strong>of</strong> high values.<br />
For 2 and 1 Hz it is a bit broader area then shown <strong>in</strong> the 3 Hz map. S<strong>in</strong>ce, <strong>in</strong> Lalitpur build<strong>in</strong>gs mostly<br />
have 3 or 4 storeys, match<strong>in</strong>g this number, the frequencies 3 and 2 Hz could be used to determ<strong>in</strong>e the<br />
most hazardous places for the new build<strong>in</strong>gs and the ones are already there. It can be <strong>in</strong>terpreted that<br />
the north; northeast and south <strong>of</strong> the site are safer than the other areas <strong>in</strong> the city for the specific storey<br />
build<strong>in</strong>gs. The Figure 5-16 was produced from the exist<strong>in</strong>g thickness files for the subsurface geology.<br />
The formula used is:<br />
F= Vs /4 * H<br />
Where; F is the fundamental soil frequency, Vs is the shear wave velocity and H is the thickness <strong>of</strong> the<br />
soil taken from total thickness map produced by Piya, 2004. This formula also represents the firstmode<br />
(resonant) frequency if we replace the shear wave velocity with the arithmetic average <strong>of</strong> it<br />
with<strong>in</strong> the thickness <strong>of</strong> soil considered. For this we can assume that the generalized pr<strong>of</strong>ile represents<br />
the general sett<strong>in</strong>g <strong>in</strong> the site. Then, the shear wave velocities used can be calculated for the arithmetic<br />
average Vs. Then, for the layers the Vs; from the surface to the bedrock respectively is 450, 600 and<br />
1700 m/s. The average makes 916 m/s. If we also consider the average thickness to be 257 m read<br />
from the histogram <strong>of</strong> the total thickness map. Then, the formula gives ~1 (0.89) and corresponds with<br />
the 10 storey build<strong>in</strong>gs <strong>in</strong> the area. The largest spectral amplifications will happen <strong>in</strong> this range <strong>of</strong> frequencies<br />
and the match<strong>in</strong>g build<strong>in</strong>g storeys; 10 (Ni, Siddharthan et al. 1997). For now, Lalitpur does<br />
not have such high build<strong>in</strong>gs but <strong>in</strong> the future there will be probably build<strong>in</strong>gs as high as 10 storeys<br />
and even higher.<br />
80<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
For the representative shear wave velocities, 500, 800 and 1500 m/s were chosen. They slightly represent,<br />
the Clay, Sand and Gravel layers <strong>of</strong> the generalized pr<strong>of</strong>ile.<br />
The Figure 5-15 assesses the relations between frequencies and <strong>in</strong>tensity and thickness. In general, the<br />
high spectral acceleration values correspond to the high MMI <strong>in</strong>tensity X. Though, the densest part <strong>of</strong><br />
the city does not match with the high spectral accelerations, the spot on the 3 frequency map show that<br />
this part would have suffered severely also. Look<strong>in</strong>g at the Figure 5-15; if we consider the actual situation<br />
which would correspond to the 500 and 800 shear wave velocities s<strong>in</strong>ce we are certa<strong>in</strong> that the<br />
there exists a thick unconsolidated layer beneath the city. Then, form 2 to 5 storey build<strong>in</strong>gs would be<br />
<strong>in</strong> unsafe situation <strong>in</strong> a worst scenario case like shown. Formerly, it was mentioned that the first mode<br />
frequency for the city was ~1 Hertz (10 storey). But, the thickness maps also show that <strong>in</strong> case <strong>of</strong><br />
earthquake not only 10 storey build<strong>in</strong>gs, but also 2, 3, 4 and 5 storey build<strong>in</strong>gs would receive the highest<br />
damage.<br />
Overall conclusions for this method;<br />
• When we compared the generalized soil pr<strong>of</strong>iles response model with the actual boreholes <strong>in</strong><br />
several ways presented before, the correlation between them was not good enough to use <strong>in</strong>stead<br />
<strong>of</strong> each other. For <strong>in</strong>stance it is not advised to use the generalized pr<strong>of</strong>ile <strong>in</strong>stead <strong>of</strong> an<br />
actual borehole log s<strong>in</strong>ce they differ <strong>in</strong> their response spectrum curves, which is essential to relay<br />
on <strong>in</strong> order to create an accurate build<strong>in</strong>g code for the area for build<strong>in</strong>g vulnerability studies.<br />
• The natural resonance maps were generally clustered <strong>in</strong> the northwest <strong>of</strong> the city for all the<br />
chosen values (1, 2, 3 and 5). The thickness <strong>of</strong> this place is less then the rest <strong>of</strong> the city. Generally<br />
thick sediments are known for their behaviour <strong>of</strong> <strong>in</strong>creas<strong>in</strong>g the accelerations compar<strong>in</strong>g<br />
to the other geological situations. But this was not clearly shown by the maps produced. It can<br />
be <strong>in</strong>terpreted that for the frequencies chosen the th<strong>in</strong>ner part produced higher values.<br />
• For a good result it seems the shear wave velocity is very essential <strong>in</strong> all cases.<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 81
Methodology 2 Input and Output Relations.<br />
Four-layer Model<br />
(Generalized <strong>Soil</strong><br />
Pr<strong>of</strong>ile)<br />
Input Motion<br />
Synthetic Earthquake<br />
with M=8 R= 48 km.<br />
Shake2000<br />
PGA (Peak<br />
Ground<br />
Acceleration)<br />
Values (g)<br />
Figure 5-14 The second methodology’s <strong>in</strong>puts and outputs. The first part represents the calculations with Shake 2000. The second part was done <strong>in</strong> ILWIS us<strong>in</strong>g 60<br />
po<strong>in</strong>ts derived from the 500 m pixel sized thickness map.<br />
82<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
Figure 5-15 Graph show<strong>in</strong>g the resonance maps correspond<strong>in</strong>g to frequencies; 1, 2, 3 and 5 Hz and the MMI<br />
map for the worst scenario earthquake and soil thickness map.<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 83
Figure 5-16 The natural frequency maps for 500, 800 and 1500 m/s shear wave velocities.<br />
84<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
6. <strong>Sensitivity</strong> <strong>Analysis</strong><br />
6.1. Methodology<br />
The objective <strong>of</strong> this study is to assess the sensitivity <strong>of</strong> the parameters that can be used to determ<strong>in</strong>e a<br />
microzonation study <strong>in</strong> Kathmandu Valley. The use <strong>of</strong> 1D horizontally layered soil pr<strong>of</strong>ile response<br />
analysis, which is broadly used, such as this one requires specific parameters. This analysis could be done<br />
us<strong>in</strong>g the Shake2000 s<strong>of</strong>tware, which is also a popular approach. But, to do this ground response analysis,<br />
detailed geotechnical (shear wave velocity, unit weight etc.), geometrical (thickness <strong>of</strong> soils) and seismological<br />
(Input Signal) parameters are needed. It is very <strong>of</strong>ten the case that all these data are not available<br />
and/or gathered with less accuracy. Most <strong>of</strong> the time, an expert’s knowledge on the <strong>in</strong>put parameter will<br />
be needed to fill the gap <strong>of</strong> data. Under these circumstances, the objective <strong>of</strong> this study is to use a sensitivity<br />
analysis to understand the natural variation <strong>of</strong> the parameters, additionally; the objective is to assess<br />
their effect on the output <strong>of</strong> the response analysis.<br />
Unless expensive <strong>in</strong>vestigations (such as seismic and electrical surveys etc.) are carried out, the exact<br />
value range <strong>of</strong> shear wave velocity, soil depth and acceleration values are not well understood or solved<br />
<strong>in</strong> the concept <strong>of</strong> soil site analysis. These <strong>in</strong>put parameters have close relations among themselves. Shear<br />
wave velocity and soil depth are the most important parameters <strong>in</strong> response analysis and they <strong>in</strong>fluence<br />
the acceleration values received on the surface. In this research, there were no real values for shear wave<br />
velocity available that have been measured <strong>in</strong> Kathmandu valley itself, unit weights were only available<br />
from a limited number <strong>of</strong> boreholes, as is the soil depth. Also a real earthquake accelerograph record,<br />
which is needed to apply the numerical response analysis, was miss<strong>in</strong>g for Kathmandu valley, as there is<br />
no network <strong>of</strong> accelerographs. In an attempt to address the parameter selection and range <strong>of</strong> values for the<br />
parameters, a sensitivity analysis is applied. Every type <strong>of</strong> analysis always <strong>in</strong>cludes a certa<strong>in</strong> degree <strong>of</strong><br />
uncerta<strong>in</strong>ty, as the range <strong>of</strong> <strong>in</strong>put parameters is almost never fully understood. Likewise, both the numerical<br />
or experimental seismic microzonation techniques need a critical evaluation <strong>of</strong> the results, which<br />
should preferably be done quantitatively. This could be done us<strong>in</strong>g various statistical uncerta<strong>in</strong>ty and/or<br />
sensitivity techniques. Pr<strong>in</strong>cipally, they are divided <strong>in</strong>to four:<br />
1. <strong>Sensitivity</strong> test<strong>in</strong>g;<br />
2. Analytical methods (Green’s function, Differential analysis etc.);<br />
3. Sampl<strong>in</strong>g based methods (Monte Carlo and Lat<strong>in</strong> hypercube, Fourier Amplitude <strong>Sensitivity</strong> Test<br />
<strong>Response</strong> Surface etc.);<br />
4. Computer algebra methods (ADIC, ADIFOR, etc) (Isukapalli 1999)<br />
<strong>Sensitivity</strong> test<strong>in</strong>g focuses on the set <strong>of</strong> changes, <strong>in</strong> the model us<strong>in</strong>g one variable and the rest as constant<br />
parameters. Analytical methods, reformulate the orig<strong>in</strong>al method with algebraic equations. Sampl<strong>in</strong>g<br />
based methods uses the orig<strong>in</strong>al model with different comb<strong>in</strong>ations for one <strong>of</strong> the <strong>in</strong>put parameters for<br />
numerous<br />
trials. The last one is the automatic differentiation, which is called computer algebra method. Most <strong>of</strong> the<br />
mentioned techniques <strong>in</strong>volve heavy mathematics and understand<strong>in</strong>g <strong>of</strong> statistics. On the contrary, the<br />
technique applied <strong>in</strong> this study is relatively easier <strong>in</strong> the theory part.<br />
The sensitivity test<strong>in</strong>g applied <strong>in</strong> this research is a straightforward technique. This technique does not use<br />
the model equations and codes like the other more complex techniques. It establishes a relationship be-<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 85
tween the <strong>in</strong>puts and outputs <strong>of</strong> the model. And also, it assesses the behaviour <strong>of</strong> the parameter selected<br />
for the analysis. Firstly, a general knowledge on the importance <strong>of</strong> the <strong>in</strong>put parameters is needed. From<br />
the beg<strong>in</strong>n<strong>in</strong>g <strong>of</strong> this study, the shear wave velocity and depth were known for their significance <strong>in</strong> soil<br />
site response. Therefore, the sensitivity analysis was applied for these two factors <strong>in</strong>itially. Secondly, the<br />
general ranges <strong>of</strong> values for these parameters were determ<strong>in</strong>ed. For example for shear wave velocity the<br />
possible range was between 100 and 10.000 feet per second. Then, the s<strong>of</strong>tware; Shake2000 was run for<br />
numerous times us<strong>in</strong>g the def<strong>in</strong>ed pair values. F<strong>in</strong>ally, the output value to assess the result was the PGA<br />
value. This value was chosen because; it is believed that it represents the soil site response better than the<br />
peak ground velocity and displacement values. In essence, the result<strong>in</strong>g table <strong>in</strong>cluded the shear wave<br />
values and their correspondence PGA values. F<strong>in</strong>ally, the values are plotted aga<strong>in</strong>st each other and a fitt<strong>in</strong>g<br />
polynomial function is derived from it us<strong>in</strong>g the least square method. A schematic overview <strong>of</strong> the<br />
method is given <strong>in</strong> Figure 6-1.<br />
INPUT PARAMETERS<br />
Shear wave<br />
velocity<br />
Variable<br />
OUTPUT<br />
Unit weight<br />
<strong>Soil</strong> thickness<br />
One <strong>of</strong> the<br />
variables<br />
İs chosen for<br />
the calculations.<br />
The rest is<br />
Kept<br />
constant.<br />
SHAKE2000<br />
PGA (g)<br />
Variable values<br />
Earthquake<br />
Figure 6-1 Methodology <strong>of</strong> the sensitivity analysis. In the analysis shear wave velocity unit weight and thickness<br />
had been also variables. The program was run for the selected range <strong>of</strong> values for the variables and the<br />
output PGA values are plotted aga<strong>in</strong>st the variable values.<br />
The variable shear wave velocity has also been replaced by thickness and unit weight. Also for these variables,<br />
a two layer and a three-layer soil pr<strong>of</strong>ile model has been applied. Variations <strong>in</strong> earthquakes <strong>in</strong>put<br />
motions could also be assessed us<strong>in</strong>g this method. This is done <strong>in</strong> the first methodology <strong>of</strong> the soil site<br />
response analysis section, which applied 3 earthquakes (see Chapter 4). Therefore, the consequences for<br />
different <strong>in</strong>put motions could also be assessed from that analysis, which will be discussed <strong>in</strong> further sections.<br />
S<strong>in</strong>ce the change is detected us<strong>in</strong>g the s<strong>of</strong>tware outputs, it can be <strong>in</strong>ferred that this analysis also addresses<br />
the sensitivity <strong>of</strong> the Shake2000 s<strong>of</strong>tware.<br />
6.2. <strong>Sensitivity</strong> to changes <strong>in</strong> Shear Wave Velocity<br />
For the two-layer model, which was tested, the values that are used for shear wave velocity are between<br />
100 and 10.000 and for the three-layer model they are from 100 to 4000 feet per second. The range <strong>of</strong><br />
values has been reduced for three-layer model s<strong>in</strong>ce above 4000 fps the PGA values are chang<strong>in</strong>g <strong>in</strong> very<br />
small <strong>in</strong>tervals (See Figure 6-2 and 6-3). For the two-layer model, Sand was selected as soil type, soil<br />
damp<strong>in</strong>g and reduction modulus were chosen to be the Sand-1 and Sand-Damp<strong>in</strong>g (See chapter 4). For<br />
86<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
the thickness a value <strong>of</strong> 40 feet was selected and 0 .11 kcf for the unit weight. For Rock, which is the second<br />
layer, the thickness was empty (it is considered to be <strong>in</strong>f<strong>in</strong>ite), and the unit weight was selected to be<br />
0.14 kcf and the shear wave velocity 9842 f/s (3000 m/s). The given values are based on the discussions<br />
and the literature. Damp<strong>in</strong>g and Reduction modulus were chosen to be “Rock type” for the underly<strong>in</strong>g<br />
Rock layer. The properties <strong>of</strong> Rock did not vary throughout the sensitivity analysis. Damp<strong>in</strong>g was kept at<br />
% 5 as <strong>in</strong> all calculations. The <strong>in</strong>put motion chosen was the seismogram record for the 1971 Adak, Alaska<br />
earthquake with a M=8 and R=67 km. For the above-mentioned range <strong>of</strong> values, the calculation was done<br />
by runn<strong>in</strong>g Shake2000 for numerous times. Figure 2 shows the result<strong>in</strong>g graph, where peak accelerations<br />
are plotted aga<strong>in</strong>st the shear wave velocity values.<br />
Vs (ft/s)<br />
Poly. (Vs (ft/s))<br />
PGA (g)<br />
0.4<br />
0.35<br />
0.3<br />
0.25<br />
0.2<br />
0.15<br />
0.1<br />
0.05<br />
0<br />
0 1000 2000 3000 4000 5000 6000<br />
Vs (f/s)<br />
Figure 6-2 Calculated PGA values for different shear wave velocities. The blue dotted curve is the orig<strong>in</strong>al<br />
curve obta<strong>in</strong>ed by plott<strong>in</strong>g the two data sets aga<strong>in</strong>st each other. The p<strong>in</strong>k l<strong>in</strong>e is the trend l<strong>in</strong>e obta<strong>in</strong>ed from<br />
this orig<strong>in</strong>al curve.<br />
The graph <strong>in</strong> Figure 6-2 shows a dotted blue and a purple curve. The latter one is the direct result <strong>of</strong> the<br />
two parameters relation. The dotted curve gives high accelerations between 700 and 1750 f/s shear wave<br />
velocities. The three peaks are at respectively, 700, 1450 and 2200 f/s. The curve could also be related to<br />
the fundamental natural frequency <strong>of</strong> the soil. Given the formula, the thickness for the two layer model is<br />
40 feet:<br />
V<br />
f = s<br />
0<br />
4H<br />
For frequency 1, the Vs should be 160 s<strong>in</strong>ce the below part <strong>of</strong> the division is 4*40 feet = 160 .The effect<br />
that can be seen is the rapid <strong>in</strong>crease <strong>of</strong> the PGA values close to this value. And, the decrease values are<br />
almost fall<strong>in</strong>g to the frequencies 1 and 5, but then this pattern is also lost <strong>in</strong> the higher values. As a result,<br />
a two layer soil pr<strong>of</strong>ile with velocities around 700 and 1750 would result <strong>in</strong> worse situations than the<br />
other shear wave velocities can cause. The purple l<strong>in</strong>e curve is a 6-degree polynomial function curve, with<br />
an R 2 , which is 0.8523. The R-squared value represents the correlation between the two curves. If the<br />
number is close to 1 or 1 then, it is considered to be highly correlated. But if it is less then, 0.40 then the<br />
correlation is not good enough to compare the two l<strong>in</strong>es. The R square is given by:<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 87
R 2 = 1- SSE<br />
SST<br />
SSE= ∑ (Yi-Ỳi ) 2<br />
SST = (∑Yi 2 ) - (∑Y i ) 2 / n<br />
Here, the Y (Yi-Ỳi ) is the variable symbol for the 2 data sets used.. And the formula <strong>of</strong> the 6 th degree<br />
polynomial is:<br />
Y = -6E-23x 6 +2E-18x 5 -3E-14x 4 +2E-10x 3 -6 E-07x 2 + 0.0007x - 0.062<br />
The behaviour <strong>of</strong> the shear wave velocities for two layered soil pr<strong>of</strong>ile could be <strong>in</strong>terpreted from the<br />
above curve and formula. Once you have your shear wave velocity value (x), you can calculate the average<br />
acceleration (y) that could result. The ma<strong>in</strong> idea here is to estimate close values <strong>of</strong> acceleration for the<br />
two-layered model. On the other hand, these relations are basically for presentation. In order to use them,<br />
<strong>in</strong> a practical way, these relations should be understood better. When this analysis is done for the threelayered<br />
model, Figure 6-3 was obta<strong>in</strong>ed.<br />
PGA values for shear wave velocity sample set.<br />
0,25000<br />
0,20000<br />
PGA (g)<br />
0,15000<br />
0,10000<br />
0,05000<br />
0,00000<br />
(0,05000)<br />
Sand Clay Poly. (Sand) Poly. (Clay)<br />
0 500 1000 1500 2000 2500 3000 3500 4000 4500<br />
Vs fps<br />
Figure 6-3 The PGA values obta<strong>in</strong>ed after the runn<strong>in</strong>g <strong>of</strong> Shake2000 for the shear wave velocity sample set.<br />
The Figure 6-3 shows the two soil types selected, Sand and Clay and their response to the shear wave velocity<br />
sample set which is from 100 to 4000 f/s. Sand layer is the first layer from the surface and Clay is<br />
the second layer, then the Rock layer comes. The PGA values were read for both <strong>of</strong> the layers <strong>in</strong> one<br />
analysis so that the graph shows the two layer values. Sand is outcropp<strong>in</strong>g and Clay is with<strong>in</strong> the pr<strong>of</strong>ile<br />
for all calculations done for the sensitivity analysis. Though both <strong>of</strong> the layers are shown here, major focus<br />
is on the material, which is outcropp<strong>in</strong>g. Because, the damage will be created on the build<strong>in</strong>gs by the<br />
response <strong>of</strong> the surficial layer mostly. This range has been chosen s<strong>in</strong>ce the changes after this value are<br />
dramatically small. The values tend to lower down start<strong>in</strong>g from 2500 f/s and cont<strong>in</strong>ue till 10.000 <strong>in</strong> the<br />
calculations. The lower<strong>in</strong>g <strong>of</strong> the PGA values reach at the end 0.08 g. The curve <strong>in</strong> Figure 6-3 suggests a<br />
second-degree polynomial trend l<strong>in</strong>e with high R-square values (Sand R=0.99; Clay R=0.97). Look<strong>in</strong>g at<br />
this statistics it looks like there is almost a l<strong>in</strong>ear relation between PGA and shear wave velocities. On the<br />
88<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
contrary, this relation should not be like this. In general, low shear wave velocities create higher accelerations<br />
and higher damage on the surface. To understand and give an explanation to this phenomenon, we<br />
can refer to the shear wave velocity limitations.<br />
0,05000<br />
0,04500<br />
0,04000<br />
0,03500<br />
0,03000<br />
0,02500<br />
0,02000<br />
0,01500<br />
0,01000<br />
0,00500<br />
0,00000<br />
Series1<br />
Series2<br />
0 100 200 300 400 500 600<br />
Figure 6-4 Graph show<strong>in</strong>g the <strong>in</strong>itial analysis for PGA values obta<strong>in</strong>ed for different shear wave velocities <strong>in</strong><br />
two-layer model. Series 1 is Sand and series 2 is Clay. The x-axis shows Vs values; y-axis shows the PGA (g)<br />
values.<br />
In Figure 6-4, the expected decrease <strong>of</strong> the PGA values could be seen for the first prelim<strong>in</strong>ary part and<br />
only for the Clay layer. One <strong>of</strong> the aspects that create these high values could depend on the limitations <strong>of</strong><br />
the shear wave velocity <strong>of</strong> the specific material. For example, Rock does not have low shear wave velocities<br />
like 100 or 300 m/s. Likewise, unconsolidated materials should not have high shear wave velocities<br />
close to 1500 m/s and above. It is also effective that the other constant parameters such as damp<strong>in</strong>g, reduction<br />
modulus and unit weight are kept constant though the material changes its type while <strong>in</strong>creas<strong>in</strong>g<br />
the shear wave velocity. The below formula also creates a l<strong>in</strong>k between the rigidity, mass and the shear<br />
wave velocity.<br />
____<br />
Vs = √ µ / ρ<br />
In which µ is the elasticity parameter called rigidity (The property <strong>of</strong> a material to resist applied stress that<br />
would tend to distort it.) and ρ is the density <strong>of</strong> the material. If the general values <strong>of</strong> the chosen soil type:<br />
Sand is known then, the limitation could be def<strong>in</strong>ed for the shear wave velocity. The limitation <strong>of</strong> the<br />
shear<br />
wave velocity values are also depended on the soil type chosen with the <strong>in</strong>formation that follow to the<br />
chosen soil type. Such as, once you select Sand as the material, then the unit weight and the dynamic soil<br />
properties also reflects these material properties. In turn, this selection would also give some limitations<br />
to the calculations done. So for the specific soil pr<strong>of</strong>ile that was selected for this test it could be <strong>in</strong>terpreted<br />
that the shear wave velocity <strong>of</strong> 250 f/s is the limit. Higher values <strong>of</strong> the shear wave velocity <strong>in</strong> the<br />
graph could not be representative <strong>in</strong> this case. Apart from the above analysis, <strong>in</strong> the ground response<br />
analysis two sets <strong>of</strong> shear wave velocities were used for the boreholes and the generalized pr<strong>of</strong>ile <strong>in</strong><br />
method 1. And, the comparison result <strong>of</strong> the shear wave velocity analysis us<strong>in</strong>g two sets showed that the<br />
PGA values are affected very much with the different values <strong>of</strong> shear wave velocity.<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 89
6.3. <strong>Sensitivity</strong> to Input Motions<br />
The sensitivity analysis could also be applied to <strong>in</strong>put motions, s<strong>in</strong>ce they are also one <strong>of</strong> the <strong>in</strong>put parameters<br />
for ground response analysis. Input motions have a more direct affect on the output values;<br />
PGA’s, if the <strong>in</strong>put motion has a high magnitude then, the PGA will also have high values. But <strong>of</strong> course<br />
apart from this affect, there are other essential th<strong>in</strong>gs that change the PGA’s such as the source parameters<br />
<strong>of</strong> the focus and the distance to the location etc. In Shake2000, the <strong>in</strong>put parameters could be divided <strong>in</strong>to<br />
two types: those related to the soil material properties and those related to the earthquake motion. For the<br />
same soil pr<strong>of</strong>iles, one can apply several different <strong>in</strong>put motions, which represent different earthquakes.<br />
The earthquakes could be from the database <strong>of</strong> the s<strong>of</strong>tware or other sources <strong>of</strong> strong motion records<br />
mentioned <strong>in</strong> Chapter 4. A number <strong>of</strong> different trials have been done <strong>in</strong> the beg<strong>in</strong>n<strong>in</strong>g <strong>of</strong> the research but<br />
these did not have the same soil pr<strong>of</strong>iles. On the other hand, the Methodology 1 (Model 2), expla<strong>in</strong>ed <strong>in</strong><br />
Chapter 4, used 3 different earthquakes for the same soil pr<strong>of</strong>ile. So the sensitivity analysis could also be<br />
applied to these results obta<strong>in</strong>ed. To present the different earthquakes and the PGA values could be plotted<br />
aga<strong>in</strong>st each other (Figure 6-5).<br />
90<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
1.8<br />
Scenario Earthquakes and Their PGA Values.<br />
1.6<br />
1.4<br />
Scenario 1 Scenario 2 Scenario 3<br />
1.2<br />
PGA (g)<br />
1<br />
0.8<br />
0.6<br />
0.4<br />
0.2<br />
0<br />
0 0.2 0.4 0.6 0.8 1 1.2 1.4<br />
Amax (g)<br />
Figure 6-5: Graph show<strong>in</strong>g the PGA values that are obta<strong>in</strong>ed for the 3 different earthquakes (Scenario 1, 2,<br />
and 3) from the methodology 1 / Model 2. The black arrow shows the range <strong>of</strong> PGA’s that could be <strong>in</strong> the<br />
site. Amax is the maximum acceleration recorded <strong>in</strong> time doma<strong>in</strong> <strong>of</strong> the earthquake.<br />
Look<strong>in</strong>g at the graph (Figure 6-5); the range <strong>of</strong> PGA’s for the first scenario earthquake is between 0.17<br />
and 0.70 g. The second scenario has values between 0.32 and 1.59 g, and the last one between 0.29 and<br />
1.07 g. The po<strong>in</strong>ts <strong>in</strong> the graph related to different soil pr<strong>of</strong>iles that will result <strong>in</strong> different PGA values<br />
given the same <strong>in</strong>put motion. PGA (peak acceleration) is what is experienced by a particle on the ground.<br />
And, A max is the maximum acceleration recorded <strong>in</strong> time doma<strong>in</strong> <strong>of</strong> the earthquake. The ranges <strong>of</strong> PGA<br />
values are very different from scenario 1 when compar<strong>in</strong>g with the other 2. Almost the range is doubled<br />
for the second and third scenario. Look<strong>in</strong>g at the graph it could be concluded that the region will suffer<br />
from 0.3 to 0.9 g for sure if there is a major earthquake.<br />
Scenario Earthquake<br />
Acceleration max.<br />
(The maximum <strong>of</strong> the <strong>in</strong>put signal)<br />
<strong>in</strong> g.<br />
PGA range<br />
In g.<br />
Los Angeles Synthetic 1.19 0.32 - 1.59 1.59<br />
Northridge (SAC Steel) 0.50 0.29 - 1.07 1.07<br />
Mae Center Synthetic<br />
(RR 2B)<br />
0.074 0.17 - 0.70 0.70<br />
PGA max.<br />
In g.<br />
Table 6-1 The comparison table for the PGA ranges <strong>of</strong> the consequent scenario earthquakes.<br />
The <strong>in</strong>put motions (either synthetic or actually measured) on Rock could have high acceleration values <strong>in</strong><br />
their time doma<strong>in</strong> records. The maximum <strong>of</strong> the record is called the acceleration maximum (Table 6-1).<br />
This also characterises the <strong>in</strong>put motion severity. The three earthquakes chosen appeared to have very<br />
high values <strong>of</strong> Amax for the first two earthquakes.. This yielded the high output accelerations on the soil,<br />
which were as high as 1.59 g. These values will be discussed <strong>in</strong> the further sections <strong>in</strong> the aspect <strong>of</strong> the<br />
analysis limits.<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 91
When the response spectra are considered, the spectral accelerations reach high values such as 2g. This is<br />
also related to the limitations <strong>of</strong> the s<strong>of</strong>tware, which was used, and the analysis chosen. The large variability<br />
<strong>of</strong> the response spectra is illustrated <strong>in</strong> Figure 6-6, which shows response spectra for two different<br />
boreholes and two different earthquakes. It can be seen that the frequencies and the spectral acceleration<br />
relations for borehole B25, are giv<strong>in</strong>g different peaks for different frequencies. For example, the second<br />
scenario created higher SA (spectral accelerations) values than the first scenario. The first scenario gives<br />
the peak acceleration on the frequency <strong>of</strong> 1 Hz. But the second scenario gives a first peak at 0.7 Hz, and a<br />
second peak is at 3 Hz for both <strong>of</strong> the curves. The second earthquake gives only two major peaks and the<br />
rest is more straightforward when we compare with the first curve. If the curves are compared <strong>in</strong> more<br />
detail the SA versus frequency types will differ a lot for the two earthquakes. The same behaviour can<br />
also be seen <strong>in</strong> the response spectra for the other example <strong>in</strong> Figure 6-6 (B23). The second earthquake has<br />
an effect <strong>of</strong> smooth<strong>in</strong>g the values for SA and also <strong>in</strong>creas<strong>in</strong>g the SA values. The differences are important<br />
s<strong>in</strong>ce the different frequencies refer to different build<strong>in</strong>g storey numbers. So <strong>in</strong> this case the far end <strong>of</strong> the<br />
analysis, <strong>in</strong> the branch <strong>of</strong> the vulnerability assessment <strong>of</strong> the build<strong>in</strong>gs, changes a lot. Conclusively, the<br />
outcome <strong>of</strong> the sensitivity analysis for the earthquake variation shows that it is very important which<br />
earthquake to choose <strong>in</strong> the response analysis.<br />
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B 25 - <strong>Analysis</strong> No. 1 - Pr<strong>of</strong>ile No. 3 - Layer 1<br />
B 25 - <strong>Analysis</strong> No. 1 - Pr<strong>of</strong>ile No. 3 - Layer 1<br />
2.5<br />
3.0<br />
2.0<br />
Sa for 5% damp<strong>in</strong>g<br />
SHAKE<br />
2.5<br />
Spectral Acceleration (g)<br />
1.5<br />
1.0<br />
0.5<br />
Spectral Acceleration (g)<br />
2.0<br />
1.5<br />
1.0<br />
0.0<br />
0.1 1 10 100<br />
Frequency (Hz)<br />
A<br />
0.5<br />
0.0<br />
0.1 1 10 100<br />
Frequency (Hz)<br />
B<br />
B 23 - <strong>Analysis</strong> No. 1 - Pr<strong>of</strong>ile No. 3 - Layer 1<br />
B 23 - <strong>Analysis</strong> No. 1 - Pr<strong>of</strong>ile No. 3 - Layer 1<br />
0.8<br />
1.0<br />
Sa for<br />
SHAKE<br />
Spectral Acceleration (g)<br />
0.6<br />
0.4<br />
Spectral Acceleration (g)<br />
0.8<br />
0.6<br />
0.4<br />
0.2<br />
0.2<br />
C<br />
0.0<br />
0.1 1 10 100<br />
Frequency (Hz)<br />
0.0<br />
0.1 1 10 100<br />
Frequency (Hz)<br />
D<br />
Figure 6-6: A and C graphs show the response spectra <strong>of</strong> two boreholes (B25 and B23) for the first scenario<br />
earthquake (M=8; R=48km). B and D show the response spectra for the same boreholes but with the third<br />
scenario earthquake (M=6.7; D=6.4 km). Please note that the y-axis range is differ<strong>in</strong>g <strong>in</strong> each graph.<br />
6.4. <strong>Sensitivity</strong> for Unit Weight<br />
Unit weight is related to the water content <strong>of</strong> the soil material. The value for the unit weight depends on<br />
the material type and its water-hold<strong>in</strong>g capacity. The maximum available water-hold<strong>in</strong>g capacity occurs<br />
<strong>in</strong> the Silty loam type <strong>of</strong> soil. So the maximum unit weight value changes would be <strong>in</strong> this soil type. The<br />
difference between a saturated soil and a dry one could differ <strong>in</strong> 2 or even 3 (<strong>in</strong> KN/m 3 ) units for the parameter.<br />
But, this situation was not taken <strong>in</strong>to consideration for the analysis s<strong>in</strong>ce it would unbalance the<br />
precision with the other <strong>in</strong>put parameters. Additionally, the porosity (the empty space <strong>in</strong> a material; Absolute<br />
porosity refers to the total amount <strong>of</strong> pore space <strong>in</strong> a reservoir, regardless <strong>of</strong> whether or not that space<br />
is accessible to fluid penetration) and the degree <strong>of</strong> compaction <strong>of</strong> the soil are important when it is assessed<br />
for the amplification relation. Apart from these <strong>in</strong>formation Figure 6-7 shows the results <strong>of</strong> a sensitivity<br />
analysis for a two-layer model for differ<strong>in</strong>g unit weights.<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 93
Unit Weight (Kcf)<br />
0,35<br />
0,3<br />
0,25<br />
PGA (g)<br />
0,2<br />
0,15<br />
0,1<br />
0,05<br />
0<br />
0,00 0,02 0,04 0,06 0,08 0,10 0,12 0,14 0,16<br />
Unit Weight (Kcf)<br />
Figure 6-7: The correlation between PGA values and the unit weights (Two layer model).<br />
The calculation was done for the general value pair from 15 till 22 (KN/m 3 ) for Sand (Sand 1 <strong>in</strong> the dynamic<br />
soil properties option <strong>in</strong> the s<strong>of</strong>tware). A constant thickness <strong>of</strong> 40 feet and a shear wave velocity <strong>of</strong><br />
1640 f/s were used. Damp<strong>in</strong>g was 5% as was the case for all calculations. The <strong>in</strong>put motion chosen was<br />
the seismogram record for the 1971 Adak, Alaska earthquake with a M=8 and R=67 km. The calculation<br />
resulted <strong>in</strong> a constant PGA value <strong>of</strong> 0.3 g for all tests. So it can be concluded that unit weight is not a very<br />
important factor <strong>in</strong> the analysis, and that the model is not sensitive to changes <strong>in</strong> unit weight.<br />
However, this relation changes for the two-layer soil pr<strong>of</strong>ile (Figure 6-8). The calculations for the same<br />
pair <strong>of</strong> values <strong>of</strong> unit weight (15-22 KN/m 3 ), gave a 2 nd degree polynomial function. The calculations<br />
were done and recorded for the two layers: Sand and Clay. Sand PGA values resulted with a high R-<br />
squared number (0.9961). Clay PGA values also resulted with a good correlation (0.998). The formulas<br />
for the Sand and Clay are respectively:<br />
Y = -30.206x 2 + 8.298x - 0.3601<br />
Y = -15.809x 2 +4.2514x - 0.1503<br />
In the formula x refers to the unit weight value and y is the output PGA value.<br />
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0,25<br />
PGA (g)<br />
0,2<br />
0,15<br />
0,1<br />
0,05<br />
Sand Clay Poly. (Sand) Poly. (Clay)<br />
y = -30,206x 2 + 8,298x - 0,3601<br />
R 2 = 0,9961<br />
y = -15,809x 2 + 4,2514x - 0,1503<br />
R 2 = 0,998<br />
0<br />
0,00 0,02 0,04 0,06 0,08 0,10 0,12 0,14 0,16<br />
Unit Weight (Kcf)<br />
Figure 6-8: Unit weight and PGA relations for a two-layer soil pr<strong>of</strong>ile (Sand and Clay).<br />
In the two layer model the same properties for Sand were used as <strong>in</strong> the one-layer model described above<br />
(thickness 40 feet and shear wave velocity <strong>of</strong> 1640 f/s), The <strong>in</strong>put parameters for the Clay layer were basically<br />
the same: a thickness <strong>of</strong> 100 feet and a shear wave velocity <strong>of</strong> 1840 f/s.. The graph <strong>in</strong> Figure 6-8<br />
<strong>in</strong>dicates that the Sand layer has higher PGA values than the Clay layer. Also, Sand has a more rapid <strong>in</strong>crease<br />
for the PGA values. In general it can be concluded that, unit weight variations create only slight<br />
changes <strong>in</strong> PGA values. For <strong>in</strong>stance, the <strong>in</strong>crease from the m<strong>in</strong>imum unit weight value to the maximum<br />
affects the PGA values for 0.158 to 0.208 (0.50 g difference for Sand layer).<br />
6.5. <strong>Sensitivity</strong> for soil thickness<br />
For the sensitivity analysis <strong>of</strong> the model to variations <strong>in</strong> the depth to bedrock, a two-layer as well as a<br />
three-layer model was used. Sand (Sand 1 <strong>in</strong> dynamic soil properties) and Clay (Clay PI=0) were used,<br />
and damp<strong>in</strong>g was aga<strong>in</strong> 5 percent. The shear wave velocity <strong>of</strong> Sand was fixed at 1640 f/s and the thickness<br />
was the variable. The same earthquake was used for this analysis also (1971 Adak, Alaska earthquake<br />
with a M=8 and R=67 km). The result for the two-layer model (bedrock and soil) is shown <strong>in</strong> Figure<br />
6-9.<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 95
PGA Values for Differ<strong>in</strong>g Depth Values <strong>in</strong> Two Layer Model.<br />
Depth Poly. (Depth )<br />
0.45<br />
0.4<br />
0.35<br />
0.3<br />
PGA (g)<br />
0.25<br />
0.2<br />
0.15<br />
0.1<br />
y = -4E-11x 6 + 2E-08x 5 - 4E-06x 4 + 0.0005x 3 - 0.0312x 2 + 0.9811x - 11.878<br />
R 2 = 0.8563<br />
0.05<br />
0<br />
0 20 40 60 80 100 120 140<br />
Depth (feet)<br />
Figure 6-9 The relation between PGA values and depth difference <strong>in</strong> a two-layer model. Sand was used for<br />
the two-layer model. The Rock layer shear wave velocity was 9842 f/s.<br />
For the two-layer soil pr<strong>of</strong>ile, R-squared was calculated as 0.8563. The formula for the 6 th degree polynomial<br />
is:<br />
Y = -4E-11x 6 +2E -0.8x 5 - 4E- 0.6x 4 +0.0005x 3 - 0.0312x 2 + 0.9811x -11.878<br />
In which X = soil thickness (<strong>in</strong> feet) and Y = PGA <strong>in</strong> g. The formula given above is considered <strong>in</strong> order to<br />
extract more <strong>in</strong>formation on the data behaviour. On the other hand, this was not that helpful and these<br />
formulas are kept because they are also <strong>in</strong> the methodology <strong>of</strong> the sensitivity analysis.<br />
The graph shows two peaks, one between 32 and 59 feet and the second between 85 and 98 feet. Both <strong>of</strong><br />
the value pairs refer to an important <strong>in</strong>crease and decrease <strong>in</strong> PGA values. The difference reaches 0.25 g<br />
<strong>in</strong> the first crest. The first crest corresponds to the first 18 meters <strong>of</strong> the soil pr<strong>of</strong>ile and the second till 30<br />
meters ( Figure 6-9 uses feet as unit). As a result, it could be <strong>in</strong>ferred that the most important depth for<br />
one-layer models is the upper 30 meters. Though, the rest <strong>of</strong> the values seem to have a steady pattern,<br />
they can be considered as secondary important value pairs. To understand these pairs also, new values<br />
and calculations are needed.<br />
The next step was to analyse the three layer model (Figure 6-10).<br />
96<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
PGA Values and Thickness Relation Us<strong>in</strong>g the Two-layer Model.<br />
Sand Clay Poly. (Sand) Poly. (Clay)<br />
0.2<br />
0.15<br />
PGA (g)<br />
0.1<br />
0.05<br />
0<br />
0 50 100 150 200 250 300 350<br />
Thickness (feet)<br />
Figure 6-10 Two-layer model for the analysis <strong>of</strong> thickness and PGA values sensitivity results.<br />
The analysis for a three-layer model with Sand and Clay layers was done for the range <strong>of</strong> 0 - 328 feet<br />
(100 meters) with an <strong>in</strong>terval <strong>of</strong> 3.28083 feet. The same dynamic properties were used; for Clay layer the<br />
plasticity <strong>in</strong>dex was “0” and for Sand layer it was “1”.Damp<strong>in</strong>g was 5 percent as always. Additional to<br />
the two-layer <strong>in</strong>put parameters attributes, the Clay layer had 1840 f/s shear wave velocity. The curve <strong>of</strong><br />
Sand has the R-squared model as 0.959. The formula for the 6 th degree polynomial that suits the curve is:<br />
Y = -1E -15x 6 + 2E -12x 5 -1E-0.9x 4 + 4E-0.7 x 3 -5E-0.5x 2 + 0.0037x+ 0.0976<br />
For Clay the R-squared is 0.8735. Both <strong>of</strong> the layers have good correlation with the trend l<strong>in</strong>e created.<br />
The formula for Clay is:<br />
Y = -1E-15x 6 + 2E -12x 5 -1E-09x 4 +4E-0.7x 3 -5E-0.5x 2 + 0.003x + 0.0692<br />
The graph has 4 peaks but they do not show a great <strong>in</strong>crease or decrease for PGA <strong>in</strong> pattern. Both the<br />
curves look alike but Clay has less PGA values than the Sand layer. As the thickness <strong>in</strong>creases both<br />
curves gradually decrease <strong>in</strong> PGA values. The range between 6.5 and 150 feet gives the highest PGA values,<br />
therefore this range should be considered as most important. The variation <strong>in</strong> PGA is from 0.09 till<br />
0.2, which is also not a big difference but it shows the sensitive area.<br />
6.6. Conclusions on the <strong>Sensitivity</strong> <strong>Analysis</strong><br />
For the most part, sensitivity analysis gave complex results for the all parameters assessed (such as shear<br />
wave velocity, <strong>in</strong>put motions, unit weight and thickness). Though tried, it is very difficult to obta<strong>in</strong> a simple<br />
pattern for these <strong>in</strong>put parameters. S<strong>in</strong>ce the parameters and the calculations both are very sensitive, it<br />
is not advised to use the expert assumptions.<br />
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In order to give some range <strong>of</strong> values for the <strong>in</strong>put parameters, a general estimation which is based on the<br />
graphs and the <strong>in</strong>terpretations will be given.<br />
The range <strong>of</strong> values that can be <strong>in</strong>terpreted from the graphs for shear wave velocity is for two-layer<br />
model, the range is between 100 and the 3000 m/s which has basically different pattern then the 3000-<br />
10000 part <strong>of</strong> the graph. The PGA difference ranges around 0.4 g. But this pattern changes significantly<br />
<strong>in</strong> three-layer model. Almost a l<strong>in</strong>ear correlation can be seen, but this is not realistic, s<strong>in</strong>ce the shear wave<br />
velocities decrease, as the PGA’s gets higher <strong>in</strong> theory. Only Clay layer shows a decrease till 250 f/s and<br />
it is also awkward because the two layers should not behave so much differently. The consequences that<br />
create this pattern could be related to the assumption that the soil layers chosen have shear wave velocities<br />
assigned beyond their properties.<br />
For the <strong>in</strong>put motions and their range <strong>of</strong> PGA values, there could be some estimation values. The range<br />
for the scenario earthquakes for 1 and 2, PGA changes from 0.1 to 1.1 g. And this value did not <strong>in</strong>clude<br />
the third scenario, which will be discussed further. This result also co<strong>in</strong>cides with the PGA map created<br />
us<strong>in</strong>g the generalized pr<strong>of</strong>ile, which has values rang<strong>in</strong>g from 0.56 to 1.40 g. Us<strong>in</strong>g both ranges it could be<br />
summarized as 0.1 till 1.40 g is the range <strong>of</strong> PGA values for the city; Lalitpur. Additionally spectral acceleration<br />
read from the generalized pr<strong>of</strong>ile calculations gave SA start<strong>in</strong>g from 0.7 till 4.9 g for different<br />
frequencies (1, 2, 3 and 5). The maximum value will be discussed <strong>in</strong> detail <strong>in</strong> follow<strong>in</strong>g chapter.<br />
Unit weight showed no change <strong>in</strong> two-layer model. Three-layer model showed PGA values rang<strong>in</strong>g from<br />
0.12 to 0.22 g. This pattern could be <strong>in</strong>terpreted that unit weight has very less affect on the PGA values<br />
compar<strong>in</strong>g to the other ones.<br />
The other <strong>in</strong>put parameter Thickness showed, the biggest change for 32 – 59 feet correspond<strong>in</strong>g 0.15-0.38<br />
g. But, cont<strong>in</strong>ued some s<strong>in</strong>usoidal behaviour through the other thickness for the two-layer model. Threelayer<br />
model also showed some s<strong>in</strong>usoidal pattern and the biggest range created a difference <strong>of</strong> 0.08-0.2 g<br />
for the range 3-100 feet. The changes <strong>in</strong> g show that this parameter is not significant as <strong>in</strong>put motion.<br />
As a conclusion, the most important parameter seemed to be the <strong>in</strong>put motion; then shear wave velocity,<br />
then thickness and unit weight.<br />
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7. Discussion, conclusions and<br />
recommendations<br />
In this chapter the general conclusions will be presented <strong>in</strong> two parts: discussions along with recommendations<br />
and conclusions. The two ma<strong>in</strong> objectives <strong>of</strong> this study were to estimate the strong ground motions<br />
for soil site responses with the available data for Lalitpur, Nepal and to assess the sensitivity <strong>of</strong> the<br />
<strong>in</strong>put parameters for response modell<strong>in</strong>g <strong>in</strong> general. Both <strong>of</strong> them have been fulfilled, under special considerations.<br />
7.1. Discussions and Recommendations<br />
In view <strong>of</strong> the first objective an <strong>in</strong>tensity map for Lalitpur was made us<strong>in</strong>g the generalized soil pr<strong>of</strong>iles<br />
derived from the layer model by Piya (2004) and Shake2000. The orig<strong>in</strong>al map with 60 pixels <strong>of</strong> 500 by<br />
500 meters was densified <strong>in</strong>to smaller pixels and each po<strong>in</strong>t produced response parameters, such as PGA<br />
and the spectral acceleration (SA) values for specific frequencies. From these data it was possible to create<br />
a PGA map and resonance and <strong>in</strong>tensity maps. The response spectrum (which relates the SA with frequency)<br />
is the l<strong>in</strong>k between the earthquake resistant design and the ground response modell<strong>in</strong>g. It is basically<br />
used directly as <strong>in</strong>put <strong>in</strong> the dynamic analysis <strong>of</strong> structures. Therefore it is important to know the<br />
response <strong>of</strong> the soil. The four-layer soil pr<strong>of</strong>ile was created on the basis <strong>of</strong> generalized subsurface model<br />
and <strong>in</strong>terpreted parameter values. The geotechnical parameters were based on generic values based on<br />
experience and taken from literature. The result with the right scenario gave an approximated map with<br />
values for the city <strong>of</strong> Lalitpur. The question to be answered is how accurate the result<strong>in</strong>g PGA and SA<br />
maps are. The PGA values that were obta<strong>in</strong>ed from this study, us<strong>in</strong>g three earthquake scenarios that are<br />
all very close to Lalitpur (see chapter 4) were <strong>in</strong> the range <strong>of</strong> 0.2 to 0.4 g, if relatively low shear wave velocities<br />
are used, and from 0.4 to 1.4 if relatively high shear wave velocities are used. PGA values for<br />
Kathmandu valley have been estimated by JICA (2002) based on an earthquake scenario model that varies<br />
from 0.2g to 0.3g for the 1934 earthquake, whereas it is taken as 0.1g for the characterization <strong>of</strong> the<br />
earthquake zone <strong>of</strong> V accord<strong>in</strong>g to the Indian standard IS 1093-1934.<br />
The assessments <strong>of</strong> the sensitivity <strong>of</strong> the response modell<strong>in</strong>g <strong>in</strong>put parameters, which is the second objective,<br />
showed that they are very sensitive to certa<strong>in</strong> <strong>in</strong>put parameters.<br />
The results <strong>of</strong> the several runs <strong>in</strong> Shake2000 give the follow<strong>in</strong>g priority <strong>of</strong> parameters importance;<br />
1. Input motion<br />
2. Shear wave velocity<br />
3. Thickness<br />
4. Unit weight<br />
1. Input Motion<br />
Initially, the importance <strong>of</strong> the parameters was also assumed like this list. Though, some <strong>of</strong> them did not<br />
show a clear pattern, it is clear that <strong>in</strong>put motion is always very important <strong>in</strong>put <strong>in</strong> any case. The best<br />
would be to use an earthquake that is a real record from the site. S<strong>in</strong>ce, it was not available, the other options<br />
were used. The other options refer to the Shake2000 strong motion database and the databases that<br />
can be obta<strong>in</strong> through Internet (NGDC 2002; MCEER 2004). Based on discussions with experts (J.P.<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 99
Avouac, personal communication) and consider<strong>in</strong>g the geological sett<strong>in</strong>g <strong>of</strong> the area, a synthetic strong<br />
motion was used <strong>in</strong> the analysis for the worst scenario (M; 8; R: 48km). The results were good for the<br />
PGA and <strong>in</strong>tensity maps, but when the values <strong>in</strong> the response spectrum reached very high accelerations (4<br />
g). The maximum <strong>of</strong> the strong motions recorded are around 2.38 g so far <strong>in</strong> the databases on Internet.<br />
The reason to have such high accelerations depends on the s<strong>of</strong>t and thick soils that are used and the very<br />
severe scenario chosen. But these could not be solely the reason, because it should be possible to calculate<br />
realistic values <strong>in</strong> the given situation. To understand this behaviour other sources <strong>of</strong> <strong>in</strong>formation were assessed.<br />
Another study also had high SA values (RIED 2000), reach<strong>in</strong>g 5.9 g. The <strong>in</strong>put signal that was<br />
used <strong>in</strong> this study used a synthetic one and was derived with a Green function analysis (A mathematical<br />
representation that, <strong>in</strong> reference to earthquake shak<strong>in</strong>g, is used to represent the ground motion caused by<br />
<strong>in</strong>stantaneous slip on a small part <strong>of</strong> a fault) from the Qu<strong>in</strong>dio Earthquake (1999) In every component <strong>of</strong><br />
the acceleration time histories it could be seen that the peak were over 0.4 g. The highest acceleration was<br />
0.58 g <strong>in</strong> the North-South component. To use the earthquake record from the soil site gives already the<br />
amplification <strong>of</strong> the soil. Secondly, the record was synthetically generated. The earthquake record that<br />
was used <strong>in</strong> this study is also synthetic but it is not certa<strong>in</strong> if it is a surface record, or a record measured<br />
on hard Rock. Additionally, it should not be surface record s<strong>in</strong>ce the s<strong>of</strong>tware is for calculat<strong>in</strong>g the soil<br />
site response <strong>in</strong> respect to seismic waves com<strong>in</strong>g from Rock. A record<strong>in</strong>g <strong>in</strong> soil would help to assess the<br />
quality <strong>of</strong> the result modelled by Shake2000.<br />
From the both studies it could be <strong>in</strong>terpreted that us<strong>in</strong>g synthetic motions could reveal results exceed<strong>in</strong>g<br />
limitations if not handled with special attention <strong>in</strong> 1D l<strong>in</strong>ear response analysis s<strong>of</strong>tware. This statement is<br />
true for synthetic and real motions when the <strong>in</strong>put signal is above 0.45 g, as expla<strong>in</strong>ed <strong>in</strong> a late stage <strong>of</strong><br />
this research by one <strong>of</strong> the developers <strong>of</strong> the Shake2000 s<strong>of</strong>tware (Ordonez, personal communication). It<br />
was advised by several researches that SHAKE (mean<strong>in</strong>g also other versions) should not be used if the<br />
<strong>in</strong>put motion exceeds a given limit. Actually, us<strong>in</strong>g the <strong>in</strong>put motions beyond this acceleration means that<br />
the earthquake has a major magnitude, such as 8 and above. So, it should be correct to use SHAKE for<br />
moderate levels <strong>of</strong> shak<strong>in</strong>g, generally between 0.15 –0.35 g. And it would be suitable for earthquake resistant<br />
design procedures s<strong>in</strong>ce beyond this limit it is really hard to construct a resistant build<strong>in</strong>g for a reasonable<br />
cost especially <strong>in</strong> develop<strong>in</strong>g countries.<br />
Under these circumstances, Shake2000 is advised to be used only for the moderate levels <strong>of</strong> shak<strong>in</strong>gs.<br />
Secondly, when choos<strong>in</strong>g an <strong>in</strong>put motion to run the analysis, the parameters that should be evaluated are<br />
not only the magnitude and distance but also the <strong>in</strong>put signals maximum acceleration <strong>in</strong> the time history<br />
components (North-South; East-West; Vertical).<br />
2. Shear wave velocity<br />
Com<strong>in</strong>g back to the priority list; the behaviour <strong>of</strong> the model under different shear wave velocities did not<br />
lead to clear results <strong>in</strong> the sensitivity analysis. The expected decrease <strong>of</strong> acceleration with <strong>in</strong>creas<strong>in</strong>g shear<br />
wave velocities was not shown <strong>in</strong> the result<strong>in</strong>g graphs. In fact, the results were contrary to that. The reason<br />
for the result<strong>in</strong>g pattern could be very much related to the analysis technique at first hand. The assumption<br />
<strong>of</strong> hav<strong>in</strong>g a very wide range <strong>of</strong> shear wave values for a s<strong>in</strong>gle layer could not show realistic values,<br />
s<strong>in</strong>ce every material has its own ranges. For this parameter, more detailed analysis should be carried<br />
out. For example, the behaviour can be assessed to different soil layers and crosschecked with the real<br />
geotechnical values.<br />
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But this situation could also be argued <strong>in</strong> another way. If we consider that the theoretically shear wave<br />
velocities could get higher as PGA values gets higher, then the explanation could refer to the soil react<strong>in</strong>g<br />
more stiff to the shear waves produced by the <strong>in</strong>put motion. High shear wave velocities relates to high<br />
shear modulus and this results <strong>in</strong> more stiff soils. Depend<strong>in</strong>g on the <strong>in</strong>put signal characteristics this could<br />
refer to high amplifications <strong>in</strong> high frequencies and high PGA and SA values.<br />
Another subject that should be po<strong>in</strong>ted out is the 30-meter shear wave velocity approach (Borcherdt<br />
1994). He proposed that certa<strong>in</strong> period <strong>of</strong> amplification factors used to scale design spectrum could be<br />
calculated as a cont<strong>in</strong>uous function <strong>of</strong> mean shear wave velocity <strong>in</strong> the top 30 m. But this was not seen <strong>in</strong><br />
the analysis <strong>of</strong> Darragh and Idriss study (1997) where they have assessed the shear wave velocity for the<br />
top 30 meters <strong>in</strong> two sites <strong>in</strong> California and found that the variation was about 60%, therefore not very<br />
applicable. This could be also assessed us<strong>in</strong>g def<strong>in</strong>ed shear wave velocities and 30 meters thickness us<strong>in</strong>g<br />
sensitivity analysis (For the same soil pr<strong>of</strong>ile, different Vs and thickness pairs could be assessed for PGA<br />
values and see their difference)<br />
Shear wave velocity changes with depth also. And this is also an important effect and should be considered<br />
<strong>in</strong> more detailed studies. If the change <strong>in</strong> shear wave velocity is not known <strong>in</strong>itially, some derived<br />
formulas can be used (refer to (Ni, Siddharthan et al. 1997)). Due to time constra<strong>in</strong>ts, the <strong>in</strong>crease <strong>of</strong> shear<br />
wave velocity was depth has not been taken <strong>in</strong>to account <strong>in</strong> this study.<br />
3. Thickness<br />
Thickness showed two important peaks around the first 30 meters and slightly <strong>in</strong> the three-layer model.<br />
This range revealed important changes <strong>in</strong> PGA values. Also, it was obvious that through great thickness<br />
the PGA value was decreas<strong>in</strong>g. This could be <strong>in</strong>terpreted that very thick sediments are considered stiffer<br />
regard<strong>in</strong>g to the calculations. Also for the thickness-acceleration relation, the result<strong>in</strong>g correlation was<br />
opposite to the one expected <strong>in</strong>itially. The <strong>in</strong>itial hypothesis that acceleration would <strong>in</strong>crease with <strong>in</strong>creas<strong>in</strong>g<br />
depth (keep<strong>in</strong>g all other factors constant), had to be rejected. With <strong>in</strong>creas<strong>in</strong>g depth, acceleration values<br />
were decreas<strong>in</strong>g.<br />
Above statement refers to the general behaviour <strong>of</strong> the curve obta<strong>in</strong>ed for thickness and PGA values. On<br />
the other hand the curve also showed a s<strong>in</strong>usoidal pattern, which could also be much related to the stand<strong>in</strong>g<br />
waves, formed while the waves are at specific depths.<br />
5. Unit Weight<br />
Unit weight has shown very slight differences <strong>in</strong> the analysis and it appears to be the least important parameter,<br />
because it showed less correlation with PGA values <strong>in</strong> the sensitivity analysis. It is debatable<br />
whether it is appropriate not to <strong>in</strong>clude this parameter <strong>in</strong> the calculations. A better understand<strong>in</strong>g <strong>of</strong> all the<br />
parameters and the calculation is needed to support such an idea.<br />
In this study the difference between the use <strong>of</strong> saturated and dry unit weights was not evaluated due to<br />
time constra<strong>in</strong>ts. On the other hand, it was noted that the pore water is very effective on the strong ground<br />
motion and should not be left out <strong>in</strong> the assessment <strong>of</strong> seismic hazard (Ni, Siddharthan et al. 1997).<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 101
Based on the results <strong>of</strong> the sensitivity analysis done <strong>in</strong> this research, several recommendations can<br />
be made for future work:<br />
1. The <strong>in</strong>put motion used should be under the 0.45 g limit so that the s<strong>of</strong>tware works properly.<br />
2. It will be better to assess these (Vs, UW, Thickness and <strong>in</strong>put motion) parameters <strong>in</strong> several<br />
situations, such as the material was generally accepted as Sand and Clay; this could be also done<br />
to others (Silt, Gravel etc).<br />
3. The range <strong>of</strong> the geotechnical data, such as unit weight or shear wave velocities should be more<br />
accurate, better us<strong>in</strong>g actual test data from the project area.<br />
4. Trial number <strong>of</strong> the sensitivity analysis could be <strong>in</strong>creased<br />
5. A more sophisticated sensitivity/uncerta<strong>in</strong>ty (Computer Algebra methods etc) analysis could be<br />
applied improve the detection <strong>of</strong> relationship patterns.<br />
L<strong>in</strong>ear approach<br />
Though the non-l<strong>in</strong>earity is accounted for through the use <strong>of</strong> modulus reduction curves and damp<strong>in</strong>g, the<br />
l<strong>in</strong>ear approach used <strong>in</strong> this study could also be less representative then a non-l<strong>in</strong>ear approach that <strong>in</strong>cludes<br />
the soil sites non-l<strong>in</strong>earity, which is very important to thick s<strong>of</strong>t soil sites. Not only the <strong>in</strong>put signal<br />
created the high accelerations <strong>in</strong> the response spectrums, but also the deep s<strong>of</strong>t soil deposits produced<br />
them. Deep s<strong>of</strong>t soils are a special case for the geotechnical problems, especially <strong>in</strong> response models.<br />
Many settlements are constructed over quaternary bas<strong>in</strong>s, with lacustr<strong>in</strong>e deposits such as Kathmandu,<br />
Lalitpur, Mexico etc. And also, these soils could also be saturated and create more complex behaviour for<br />
an earthquake. So it is important to understand these soil sites <strong>in</strong> detail. A better response analysis for<br />
such sites uses the non-l<strong>in</strong>ear approach.<br />
It is mentioned that s<strong>of</strong>t soils are also responsible <strong>of</strong> creat<strong>in</strong>g such high accelerations. The reason for this<br />
statement comes from the analysis details, which depends on the dynamic material properties used and the<br />
<strong>in</strong>put motions comb<strong>in</strong>ation. If the <strong>in</strong>put motion used causes shear stra<strong>in</strong>s (Angular displacement <strong>of</strong> a<br />
structural member due to a force act<strong>in</strong>g across it, measured <strong>in</strong> radius) greater than the shear stra<strong>in</strong> used to<br />
def<strong>in</strong>e the dynamic material properties, the acceleration values get higher (Ordonez, personal communication).<br />
The solution for this is to use a material that covers these levels <strong>of</strong> shear stra<strong>in</strong>s. But, <strong>in</strong> case <strong>of</strong> actual<br />
boreholes, or even the generalized four-layer model, it is not possible to change the material. Above<br />
all, if the <strong>in</strong>put motion is produc<strong>in</strong>g more than %3 shear stra<strong>in</strong> then the l<strong>in</strong>ear approach is not applicable<br />
<strong>in</strong> Shake (Ordonez, personal communication).<br />
A support<strong>in</strong>g statement summarizes that the s<strong>of</strong>t soils may plastify, s<strong>of</strong>ten and fail <strong>in</strong> given specific levels<br />
<strong>of</strong> <strong>in</strong>put acceleration (Seed, Dickenson et al. 1992). They also mention that l<strong>in</strong>ear approaches do not produce<br />
good results when this fail<strong>in</strong>g and s<strong>of</strong>ten<strong>in</strong>g happens. In the analysis the peak shear stresses with<strong>in</strong><br />
critical soil zones may exceed the actual dynamic strengths <strong>of</strong> soils and the result gives over prediction <strong>of</strong><br />
PGA’s <strong>in</strong> high frequency motions.<br />
The same study assess the l<strong>in</strong>ear and non-l<strong>in</strong>ear approaches gives the follow<strong>in</strong>g result response spectrum<br />
(Figure 7.1) The <strong>in</strong>put motion that is used for the analyses is a transverse (S-waves) component <strong>of</strong> the<br />
Yerba Buena Island record which is scaled to A max= 0.07g (Seed, Dickenson et al.). The given graph<br />
shows that l<strong>in</strong>ear approach results <strong>in</strong> higher SA values than, the non-l<strong>in</strong>ear (MARDES; non-l<strong>in</strong>ear s<strong>of</strong>tware)<br />
approach. The site has also similar characteristics as Lalitpur; deep s<strong>of</strong>t soils <strong>of</strong> San Francisco Bay<br />
region. Another po<strong>in</strong>t that should be referred is that the <strong>in</strong>put signal they are us<strong>in</strong>g is real and does not<br />
exceed the 0.45 g limit but the calculated results show moderate-high accelerations.<br />
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Figure 7-1 The response spectrum show<strong>in</strong>g the l<strong>in</strong>ear and non-l<strong>in</strong>ear approach results; SHAKE is l<strong>in</strong>ear and<br />
MARES is the non-l<strong>in</strong>ear. Compare the maximum and the difference between the two.<br />
Then, with high shear stra<strong>in</strong>s and specific material it is advised to use the non-l<strong>in</strong>ear approach. When it is<br />
required to analyse a worst scenario case, which has higher accelerations then 0.45 g, the analysis approach<br />
should be non-l<strong>in</strong>ear, if not the l<strong>in</strong>ear approach also predicts pr<strong>of</strong>iciently.<br />
<strong>Response</strong> <strong>Modell<strong>in</strong>g</strong><br />
If we consider that every geotechnical parameter needed for an ideal soil site response analysis is gathered,<br />
the earthquake is recorded at that site and the general subsurface geology is known <strong>in</strong> 3D, one <strong>of</strong> the<br />
best analyses could be done. On the other hand there are still some gaps that are very hard to fill. These<br />
gaps refer to the assumptions that are accepted from the beg<strong>in</strong>n<strong>in</strong>g. This is the l<strong>in</strong>earity <strong>of</strong> the soil sites,<br />
though they are not. The subsurface geology is very complex <strong>in</strong> pattern. The soil is weathered, moved,<br />
eroded, deposited and experienced many other processes. And therefore expect<strong>in</strong>g a l<strong>in</strong>ear approach from<br />
the site is very difficult. It seems to be it would be more realistic if the non-l<strong>in</strong>ear site effects were considered<br />
<strong>in</strong> 2D or 3D (Aki 1993). For direct non-l<strong>in</strong>ear approaches the s<strong>of</strong>tware that can be used are DESRA<br />
2 (Lee and F<strong>in</strong>n 1978) and the CHARSOIL (Streeter, Wylie et al. 1974). The improved version <strong>of</strong><br />
DESRA2 could also be found (Ni, Siddharthan et al. 1997).<br />
7.2. General Conclusions<br />
• The resonance maps that are created from the generalized pr<strong>of</strong>ile could be appropriate for smaller<br />
scale projects, but for larger scales it is not sufficiently accurate. First, when compared to actual<br />
borehole log results <strong>in</strong> the response spectra are very different. Secondly, the used scenario earthquake<br />
was not suitable for the s<strong>of</strong>tware (Shake2000) to make the realistic calculations.<br />
• If the ideal site response study is done, the results <strong>of</strong> the sensitivity and the comparison <strong>of</strong> the<br />
methods show that the l<strong>in</strong>ear response analysis still needs uncerta<strong>in</strong>ty / sensitivity analysis.<br />
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• Us<strong>in</strong>g similar earthquake signals (magnitude and distance) for the same site shows that there are<br />
significant changes <strong>in</strong> the response spectra. One signal can result <strong>in</strong> high accelerations <strong>in</strong> a specific<br />
frequency and another signal can result <strong>in</strong> different behaviour. This was assessed for the actual<br />
boreholes and the generalized pr<strong>of</strong>ile. And the result demonstrates also that it is very important<br />
to use an <strong>in</strong>put signal that is characteristics for the region. This is also true for the synthetic<br />
signals generated. The study <strong>of</strong> Guatteri, Mai et al (2002), showed that variation <strong>in</strong> the specific<br />
source zone parameters, such as fault and slip type, rupture velocity and slip velocity has a great<br />
effect on the type <strong>of</strong> ground motion that is generated.<br />
• One <strong>of</strong> the research questions was if it would be possible to use a simplified two-layer model<br />
shear wave velocity <strong>in</strong>stead <strong>of</strong> multi-layer soil pr<strong>of</strong>iles. Look<strong>in</strong>g at the sensitivity analysis and the<br />
pr<strong>of</strong>iles compared, it can be <strong>in</strong>terpreted that this is not advisable, because soil pr<strong>of</strong>ile produces<br />
important changes <strong>in</strong> sensitivity analysis.<br />
• Another question was whether it is possible to establish relationship between a two-layer and a<br />
multi-layer pr<strong>of</strong>ile for a s<strong>in</strong>gle parameter. The patterns, especially for shear wave and thickness<br />
parameters, are not clear enough to derive any such relationship.<br />
• Initially, shear wave velocity was <strong>of</strong> great concern and it was opted to simplify this parameter.<br />
This simplification <strong>in</strong> any dimension (def<strong>in</strong><strong>in</strong>g standards etc) would help the analysis, lower the<br />
costs and make it easier, s<strong>in</strong>ce expensive geophysical methods were go<strong>in</strong>g to be omitted. However,<br />
the sensitivity analysis demonstrates that the shear wave velocity <strong>of</strong> the soil (which relates<br />
to the shear modulus <strong>of</strong> the soil) is too important to dismiss or generalise too much.<br />
• The generalised 2.5 D boundary layer subsurface model did not accurately predict the correct response<br />
at 14 specific locations where more detailed subsurface <strong>in</strong>formation was available <strong>in</strong> the<br />
form <strong>of</strong> borehole record.<br />
• When us<strong>in</strong>g either a L<strong>in</strong>ear or non-l<strong>in</strong>ear approach it is advised to give attention on the parameter<br />
sensitivity because <strong>of</strong> the fully non-l<strong>in</strong>ear soils also employ parameters which can be difficult to<br />
evaluate, but which can have a significant impact on result<strong>in</strong>g calculations (Seed, Dickenson et<br />
al.). Particularly when large magnitude and large duration earthquakes are simulated, which result<br />
<strong>in</strong> exceedance <strong>of</strong> the shear strength <strong>of</strong> the soil, and <strong>in</strong> turn results <strong>in</strong> high stra<strong>in</strong> values, cannot be<br />
accurately validated <strong>in</strong> the SHAKE-based modell<strong>in</strong>g approach.<br />
104<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
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• Zaslavsky, Y. (2001). Microzon<strong>in</strong>g <strong>of</strong> the earthquake hazard <strong>in</strong> Israel, Earth Sciences research adm<strong>in</strong>istration national<br />
m<strong>in</strong>istry <strong>of</strong> <strong>in</strong>frastructures and the m<strong>in</strong>istry <strong>of</strong> absorption. 2003.<br />
• Zhang, P., Z.-x. Yang, et al. (1992-1999). Global <strong>Seismic</strong> Hazard Assessment Program (GSHAP) <strong>in</strong> Cont<strong>in</strong>ental Asia,<br />
UN/IDNDR. 2003.<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 107
108<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
Appendix A: Input Strong Ground Motion (3 Scenario)<br />
MAE Center RR 2B Synthetic, M= 8, R= 48km (hypocentral distance) seismogram records for acceleration,<br />
velocity and displacement records.<br />
0.5<br />
MAE Center RR-2B Project - Synthetic Ground Motion - Ground Surface<br />
0.4<br />
0.3<br />
Acceleration (g)<br />
0.2<br />
0.1<br />
0.0<br />
-0.1<br />
-0.2<br />
-0.3<br />
-0.4<br />
-0.5<br />
0 20 40 60 80 100<br />
Time (sec)<br />
1.5<br />
MAE Center RR-2B Project - Synthetic Ground Motion - Ground Surface<br />
1.0<br />
0.5<br />
Velocity (ft/sec)<br />
0.0<br />
-0.5<br />
-1.0<br />
-1.5<br />
-2.0<br />
0 20 40 60 80 100<br />
Time (sec)<br />
0.8<br />
MAE Center RR-2B Project - Synthetic Ground Motion - Ground Surface<br />
0.6<br />
0.4<br />
Displacement (ft)<br />
0.2<br />
0.0<br />
-0.2<br />
-0.4<br />
-0.6<br />
0 20 40 60 80 100<br />
Time (sec)<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 109
Los Angeles Simulated strong ground motion M= 7.1 D= 17.5 km (epicentral) files for acceleration,<br />
velocity and displacement records.<br />
1.5<br />
Los Angeles 2% <strong>in</strong> 50 years; Elysian Park (simulated); M: 7.1; D: 17.5 Km; 1.19g;<br />
1.0<br />
Acceleration (g)<br />
0.5<br />
0.0<br />
-0.5<br />
-1.0<br />
-1.5<br />
0 5 10 15 20 25 30<br />
Time (sec)<br />
Los Angeles 2% <strong>in</strong> 50 years; Elysian Park (simulated); M: 7.1; D: 17.5 Km; 1.19g;<br />
4<br />
3<br />
2<br />
Velocity (ft/sec)<br />
1<br />
0<br />
-1<br />
-2<br />
-3<br />
-4<br />
-5<br />
0 10 20 30 40<br />
Time (sec)<br />
1.0<br />
Los Angeles 2% <strong>in</strong> 50 years; Elysian Park (simulated); M: 7.1; D: 17.5 Km; 1.19g;<br />
0.5<br />
Displacement (ft)<br />
0.0<br />
-0.5<br />
-1.0<br />
-1.5<br />
0 10 20 30 40<br />
Time (sec)<br />
110<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
SAC steel Northridge 1994 M=6.7, D= 6.4 km (epicentral) seismogram records for<br />
acceleration, velocity and displacement records.<br />
Sylm<br />
n Northridge,17 Jan 94,04:31PST; Sylmar, Olive View FF<br />
0.6<br />
0.4<br />
0.2<br />
Acceleration (g)<br />
0.0<br />
-0.2<br />
-0.4<br />
-0.6<br />
-0.8<br />
0 10 20 30 40 50 60<br />
Time (sec)<br />
Sylm<br />
n Northridge,17 Jan 94,04:31PST; Sylmar, Olive View FF<br />
5<br />
4<br />
3<br />
Velocity (ft/sec)<br />
2<br />
1<br />
0<br />
-1<br />
-2<br />
0 20 40 60 80<br />
Time (sec)<br />
Sylm<br />
n Northridge,17 Jan 94,04:31PST; Sylmar, Olive View FF<br />
1.5<br />
1.0<br />
Displacement (ft)<br />
0.5<br />
0.0<br />
-0.5<br />
-1.0<br />
0 20 40 60 80<br />
Time (sec)<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 111
Appendix B: <strong>Soil</strong> Pr<strong>of</strong>ile Information On Calculations Done In Shake2000.<br />
meter KN/m3 m/s m/s<br />
No. Well_ID Modified Description <strong>Soil</strong> ID Thickness feet UW pcf kcf Vs- SET 1 ft/s Vs-SET2 ft/s<br />
1 B -23 Clayey Silt 1 4 13.1 17 108 0.11 250 820 500 1640<br />
Medium to coarse Sand 2 11.08 36.4 18 115 0.11 600 1968 450 1476<br />
Silty Sand 2 12.2 40.0 18 115 0.11 600 1968 450 1476<br />
Gravelly Sandy Clay 3 18.28 60.0 16 102 0.10 300 984 600 1968<br />
Sandy Clay 3 30.48 100.0 16 102 0.10 300 984 600 1968<br />
Sandy Clay 3 97.37 319.5 16 102 0.10 300 984 600 1968<br />
Sandy Gravel 4 42.47 139.3 20 127 0.13 1000 3281 700 2297<br />
Sandy Clay 3 33.43 109.7 16 102 0.10 300 984 750 2461<br />
Sandy Clay 3 54.86 180.0 16 102 0.10 300 984 750 2461<br />
Rock 5 0.0 22 140 0.14 3000 9842 3000 9842<br />
2 B - 24 Clay 1 41.14 135.0 16 102 0.10 300 984 600 1968<br />
Gravels and Boulders 2 18.9 62.0 20 127 0.13 1000 3281 1850 6070<br />
Rock 3 0.0 22 140 0.14 3000 9842 3000 9842<br />
3 B - 25 Clay 1 105.76 347.0 16 102 0.10 300 984 600 1968<br />
Gravelly Clay 1 6.1 20.0 16 102 0.10 300 984 850 2789<br />
Gravel 2 22.55 74.0 20 127 0.13 1000 3281 1700 5577<br />
Rock 3 1.71 5.6 22 140 0.14 3000 9842 3000 9842<br />
4 B1 F<strong>in</strong>e Sand 1 6.4 21.0 18 115 0.11 600 1968 750 2461<br />
112<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
F<strong>in</strong>e to medium Sand 1 2.74 9.0 18 115 0.11 600 1968 750 2461<br />
F<strong>in</strong>e to coarse Sand 1 6.1 20.0 18 115 0.11 600 1968 800 2625<br />
Clay 2 70.26 230.5 16 102 0.10 300 984 600 1968<br />
Clay 2 5.94 19.5 16 102 0.10 300 984 600 1968<br />
Clay 2 83.31 273.3 16 102 0.10 300 984 600 1968<br />
Gravelly Clay 2 38.55 126.5 16 102 0.10 300 984 850 2789<br />
Gravelly Sand with Clay 3 9.14 30.0 18 115 0.11 300 984 1200 3937<br />
Clay 2 97.54 320.0 16 102 0.10 300 984 600 1968<br />
F<strong>in</strong>e to Corse Sand 1 5.72 18.8 18 115 0.11 600 1968 1200 3937<br />
Sandy Clay 2 9.16 30.1 16 102 0.10 300 984 800 2625<br />
Sandy Clay 2 15.24 50.0 16 102 0.10 300 984 800 2625<br />
Gravelly Sand with Clay 3 21.32 69.9 18 115 0.11 300 984 1100 3609<br />
Sandy Clay 2 15.25 50.0 16 102 0.10 300 984 800 2625<br />
Clayey Sand 1 6.09 20.0 18 115 0.11 600 1968 1000 3281<br />
Silty Sandy Clay 2 9.14 30.0 16 102 0.10 300 984 1000 3281<br />
Medium to coarse Sand 2 24.39 80.0 18 115 0.11 600 1968 1100 3609<br />
Clayey Sand 2 24.39 80.0 18 115 0.11 600 1968 1000 3281<br />
Sandy Clay 1 6.1 20.0 16 102 0.10 300 984 800 2625<br />
Rock 4 22 140 0.14 3000 9842<br />
5 DMG 13 Clay 1 55 180.4 16 102 0.10 300 984 600 1968<br />
Clayey Sand 2 10 32.8 18 115 0.11 600 1968 1000 3281<br />
Clay 1 21 68.9 16 102 0.10 300 984 600 1968<br />
Clayey Silty Sand 2 3 9.8 18 115 0.11 600 1968 1100 3609<br />
Clay 1 64 210.0 16 102 0.10 300 984 600 1968<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 113
medium to coarse Sand 2 5 16.4 18 115 0.11 600 1968 1200 3937<br />
Clay 1 5 16.4 16 102 0.10 300 984 600 1968<br />
Medium to coarse Sand 2 11 36.1 18 115 0.11 600 1968 1200 3937<br />
Clay 1 6 19.7 16 102 0.10 300 984 600 1968<br />
Medium to coarse Sand 2 10 32.8 18 115 0.11 600 1968 1200 3937<br />
Clay 1 5 16.4 16 102 0.10 300 984 600 1968<br />
medium to coarse Sand 2 6 19.7 18 115 0.11 600 1968 1200 3937<br />
Clay 1 4 13.1 16 102 0.10 300 984 600 1968<br />
medium to coarse Sand 2 18 59.1 18 115 0.11 600 1968 1200 3937<br />
Clay 1 17 55.8 16 102 0.10 300 984 600 1968<br />
medium to coarse Sand 2 8 26.2 18 115 0.11 600 1968 1200 3937<br />
Clay 1 6 19.7 16 102 0.10 300 984 600 1968<br />
medium to coarse Sand 2 14 45.9 18 115 0.11 600 1968 1200 3937<br />
Clay 1 29 95.1 16 102 0.10 300 984 600 1968<br />
Rock 3 0.0 22 140 0.14 3000 9842 3000 9842<br />
6 AG 68 Clayey Silt 1 6 19.7 17 108 0.11 450 1476 750 2461<br />
Silt 1 23 75.5 17 108 0.11 450 1476 800 2625<br />
Clay 2 120 393.7 16 102 0.10 300 984 600 1968<br />
Silt 1 14 45.9 17 108 0.11 450 1476 800 2625<br />
Gravelly Sand 3 15 49.2 18 115 0.11 600 1968 1450 4757<br />
Gravel and boulder mixed 4 11 36.1 20 127 0.13 1000 3281 1850 6070<br />
Rock 5 0.0 22 140 0.14 3000 9842 3000 9842<br />
7 BHD 3 Clay 1 129 423.2 16 102 0.10 300 984 600 1968<br />
114<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
Silty Clayey Sand 2 15 49.2 18 115 0.11 600 1968 1000 3281<br />
Clay 1 25 82.0 16 102 0.10 300 984 600 1968<br />
Rock 3 0.0 22 140 0.14 3000 9842 3000 9842<br />
8 P -29 Clay 1 174 570.9 16 102 0.10 300 984 600 1968<br />
Sand and Gravel 2 44 144.4 20 127 0.13 1000 3281 1450 4757<br />
Rock 3 0.0 22 140 0.14 3000 9842 3000 9842<br />
9 P 37 Sandy Clay 1 30.6 100.4 16 102 0.10 300 984 900 2953<br />
Clayey Sand 2 3.9 12.8 18 115 0.11 600 1968 1000 3281<br />
Coarse Sand 2 5.5 18.0 18 115 0.11 600 1968 1200 3937<br />
Medium Sand 2 5 16.4 18 115 0.11 600 1968 1200 3937<br />
Clay 1 13.5 44.3 16 102 0.10 300 984 600 1968<br />
Clayey Sand 2 93 305.1 18 115 0.11 600 1968 1000 3281<br />
Medium Sand 2 3 9.8 18 115 0.11 600 1968 1200 3937<br />
Sandy Clay 1 8 26.2 16 102 0.10 300 984 900 2953<br />
Coarse Sand 2 4.5 14.8 18 115 0.11 600 1968 1200 3937<br />
Sandy Clay 1 5.5 18.0 16 102 0.10 300 984 900 2953<br />
Gravelly Sand 2 5.5 18.0 18 115 0.11 600 1968 1450 4757<br />
Clay 1 2 6.6 16 102 0.10 300 984 600 1968<br />
Gravelly Sand 2 8 26.2 18 115 0.11 600 1968 1450 4757<br />
Clay 1 6 19.7 16 102 0.10 300 984 600 1968<br />
Gravelly Sand 2 4.5 14.8 18 115 0.11 600 1968 1450 4757<br />
Clay 1 69 226.4 16 102 0.10 300 984 600 1968<br />
Gravelly Sand 2 15 49.2 18 115 0.11 600 1968 1450 4757<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 115
Clay 1 1 3.3 16 102 0.10 300 984 600 1968<br />
Coarse Sand 2 4.5 14.8 18 115 0.11 600 1968 1200 3937<br />
Clay 1 10.5 34.4 16 102 0.10 300 984 600 1968<br />
Coarse Sand 2 4 13.1 18 115 0.11 600 1968 1200 3937<br />
Clay 1 2 6.6 16 102 0.10 300 984 600 1968<br />
Coarse Sand 2 44.1 144.7 18 115 0.11 600 1968 1200 3937<br />
Clay 1 1.4 4.6 16 102 0.10 300 984 600 1968<br />
Coarse Sand 2 20 65.6 18 115 0.11 600 1968 1200 3937<br />
Rock 3 22 140 0.14 3000 9842 3000 9842<br />
0.0<br />
10 PR 16 Clay 1 45 147.6 16 102 0.10 300 984 600 1968<br />
Boulders 2 3 9.8 21 134 0.13 1500 4921 2000 6562<br />
Limestone /Rock 3 26.65 87.4 22 140 0.14 3000 9842 3000 9842<br />
0.0<br />
11 SPT 39 Sandy Clay 1 0.7 2.3 16 102 0.10 300 984 900 2953<br />
medium Sand 2 0.3 1.0 18 115 0.11 600 1968 1100 3609<br />
medium Sand 2 0.7 2.3 18 115 0.11 600 1968 1100 3609<br />
Clayey Sand 2 0.3 1.0 18 115 0.11 600 1968 1000 3281<br />
Clayey Sand 2 1 3.3 18 115 0.11 600 1968 1000 3281<br />
Clayey Sand 2 0.35 1.1 18 115 0.11 600 1968 1000 3281<br />
Clayey Sand 2 0.1 0.3 18 115 0.11 600 1968 1000 3281<br />
Clayey Sand 2 0.75 2.5 18 115 0.11 600 1968 1000 3281<br />
Clay 1 0.25 0.8 16 102 0.10 300 984 600 1968<br />
Sandy Clay 1 0.55 1.8 16 102 0.10 300 984 900 2953<br />
Clay 1 1.45 4.8 16 102 0.10 300 984 600 1968<br />
116<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
Rock 3 0.0 22 140 0.14 3000 9842 3000 9842<br />
12 SPT 25 Silty Clay 1 1 3.3 16 102 0.10 300 984 700 2297<br />
Clayey Silt 2 0.45 1.5 17 108 0.11 450 1476 750 2461<br />
Clayey Silt 2 0.55 1.8 17 108 0.11 450 1476 750 2461<br />
f<strong>in</strong>e Sandy Silt 2 0.45 1.5 17 108 0.11 450 1476 1000 3281<br />
f<strong>in</strong>e Sandy Silt 2 0.55 1.8 17 108 0.11 450 1476 1000 3281<br />
f<strong>in</strong>e Sandy Silt 2 0.45 1.5 17 108 0.11 450 1476 1000 3281<br />
f<strong>in</strong>e Sandy Silt 2 0.55 1.8 17 108 0.11 450 1476 1000 3281<br />
Sandy Clay 1 0.45 1.5 16 102 0.10 300 984 900 2953<br />
Rock 3 22 140.05 0.14 3000 9842 3000 9842<br />
13 C40 Gravel and Sandy Silt 1 0.82 2.69 15 95.487 0.10 250 820 1200 3937<br />
Clayey Silt and Gravel 2 0.88 2.89 16 101.85 0.10 300 984 700 2297<br />
Clayey Silt and Gravel 2 1.30 4.27 18 114.58 0.11 400 1312 700 2297<br />
Clayey Silt 3 3.00 9.84 17 108.22 0.11 350 1148 750 2461<br />
Sandy Silt 4 5.48 17.98 17 108.22 0.11 350 1148 900 2953<br />
Plastic Clayey Silt 5 3.97 13.03 17 108.22 0.11 350 1148 750 2461<br />
Rock 6 22 140.05 0.14 3000 9842 3000 9842<br />
14 C296 Silty Sand Gravel and cobble mixed 1 0.90 2.9529 15 95.487 0.10 250 820 300 984<br />
Gravel 2 1.50 4.9215 18 114.58 0.11 350 1148 1400 4593<br />
Rock 3 7.00 22.967 20 127.32 0.13 1000 3281 2500 8202<br />
22 140.05 0.14 3000 9842 3000 9842<br />
Shear Modu.lus 2431<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 117
6188<br />
118<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
Appendix C: Generalized <strong>Soil</strong> Pr<strong>of</strong>ile Frequency Values<br />
Frequency<br />
Hertz<br />
Pr<strong>of</strong>ile<br />
No 0.3 1 2 3 5<br />
1 0.27 1.98 2.41 1.34 0.84<br />
2 0.18 0.74 1.31 1.98 1.1<br />
3 0.17 2.87 1.88 1.97 1.1<br />
4 0.2 1.74 2.31 1.92 0.81<br />
5 0.25 1.76 2.31 1.66 0.79<br />
6 0.27 1.66 2.08 1.67 0.73<br />
7<br />
8 0.13 0.59 2.21 4.37 1.65<br />
9 0.17 2.9 2.21 2.39 1.14<br />
10 0.13 3.2 3 1.44 1.64<br />
11 0.28 1.85 2.34 1.63 0.79<br />
12 0.42 3.19 1.62 1.06 0.81<br />
13 0.11 1.7 3.5 4.9 1.62<br />
14 0.09 0.48 0.89 1.9 4.6<br />
15 0.18 4.4 3.56 2.25 1.08<br />
16 0.11 3.12 2.88 1.49 1.61<br />
17 0.18 3.3 1.71 1.21 1.01<br />
18 0.19 1.65 1.98 1.8 0.83<br />
19 0.37 3.5 1.49 1.19 0.77<br />
20 0.14 5.84 2.03 2.85 1.38<br />
21 0.14 6.03 2.41 2.7 1.52<br />
22 0.18 3.9 3.25 2.6 1.1<br />
23 0.16 2.5 2.4 1.71 1.1<br />
24 1.2 1.93 2.08 3.31 1.77<br />
25 0.26 1.67 1.44 0.98 0.68<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 119
26 0.29 1.15 1.85 1.31 0.93<br />
27 0.2 1.2 1.48 1.1 0.9<br />
28 0.24 1.31 1.24 1.25 0.77<br />
29 1.04 2.15 1.2 1.98 1.31<br />
30 0.11 0.46 0.7 1.11 1.68<br />
31 0.11 0.65 4.7 2.6 2.3<br />
32 0.15 5.52 2.06 2.9 1.35<br />
33 0.15 2.54 2.75 2.56 1.27<br />
34 0.17 1.74 2 1.59 0.83<br />
35 0.2 1.95 2.15 1.78 0.85<br />
36 0.22 2.4 2.5 1.24 0.86<br />
37 0.27 2.2 2.35 1.2 0.83<br />
38 0.21 2.8 1.9 1.15 0.84<br />
39 0.13 5.9 2.07 2.1 1.43<br />
40 0.15 2.06 2.01 1.6 0.91<br />
41 0.21 1.61 1.77 1.31 0.8<br />
42 0.21 1.73 1.75 1.36 0.74<br />
43 0.18 0.92 2.07 1.4 0.86<br />
44 0.12 1.34 1.2 1.74 1.87<br />
45 0.14 1.9 2.11 1.77 0.91<br />
46 0.22 1.62 1.7 1.4 0.82<br />
47 0.28 1.7 1.76 1.83 0.74<br />
48 0.29 1.81 1.55 1.74 0.73<br />
49 0.24 1.85 2.29 1.35 0.77<br />
50 0.21 3.4 1.75 1.33 0.85<br />
51 0.21 1.83 2.23 1.58 0.78<br />
52 0.28 0.75 1.91 1.44 0.76<br />
53 0.14 1.29 2.5 3.6 1.9<br />
54 0.57 3.6 1.46 0.96 0.84<br />
55 0.22 2.1 2.06 1.11 0.77<br />
120<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal
56 0.35 3.42 1.42 0.97 0.86<br />
57 0.4 3.13 1.13 0.95 0.69<br />
58 0.26 1.54 1.4 0.96 0.68<br />
59 0.33 2.56 1.88 1.05 0.81<br />
60 0.27 3.4 1.49 1.11 0.78<br />
<strong>Sensitivity</strong> <strong>Analysis</strong> Of <strong>Soil</strong> <strong>Site</strong> <strong>Response</strong> <strong>Modell<strong>in</strong>g</strong> In <strong>Seismic</strong> Microzonation For Lalitpur, Nepal 121