Sensitivity Analysis of Soil Site Response Modelling in Seismic ... - ITC

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2. Literature Review Sensitivity analysis can be applied to many disciplines from politics to physics. In geological hazard studies this also can be done for the input parameters for seismic response models, which is selected for this study. If it is deducted from the wider concepts of the seismic hazard assessment, the main branches include: • Seismic Hazard Assessment • Seismic Microzonation • Ground Response Modelling • Sensitivity Analysis To give a summary of the literature review of these topics, the terms and concepts that are going to be dealt in the review should be clarified. Although, in this research the focus is on sensitivity analysis, it is also based on a broader concept of Seismic hazard assessment. Seismic hazard assessment involves the quantitative evaluation of ground shaking hazards (primary hazard; earthquakes damage to the site and secondary hazards such as: fires, landslides and liquefaction etc) at a specific location. The analysis can be taken in two ways; deterministically and probabilistically. The deterministic approach uses an accepted earthquake scenario, whereas the probabilistic approach quantifies the rate (or probability) of exceeding various groundmotion levels at a site, given all possible earthquakes (Field 2001). This research follows a deterministic approach and will be based on earthquake scenarios. In seismic microzonation studies, seismological, geological, hydrogeological, topographical and geotechnical data are necessary to implement the analysis. Microzonation studies provide important information on the parameters that may be needed in planning and implementing a project done by physical planners, urban designers, engineers, architects etc. Apart from compiling input data, estimation of the ground response takes place, which is one of the most important sections in microzonation. Second, estimation of the ground response will be applied in the research focusing on the soil site effects. To model ground response, two main effects should be considered, soil site and topography effects. Soil site effects are much more commonly investigated, then the topographical effects. The main reason for that is usually, the urbanization takes place where soft soils develop, such as coastal plains and river valleys. On the other hand, topographic effects are also very important for urban areas, since settlements are generally on basins where there is a great amount of amplification due to topography. Above all, topographic amplification is very complex and needs 3D analysis in order to have better accuracy where, soil site effects could be investigated using 1D models. Since more population and more risk involved on the soil site, the estimation of these effects was more popular for the scientific community. So far the destructive earthquakes like Mexico 1985, Kobe 1995 and Turkey 1999 took 16 Sensitivity Analysis Of Soil Site Response Modelling In Seismic Microzonation For Lalitpur, Nepal
place where the ground responses were amplified because of the soil site properties. Soil site properties define the seismic wave behaviour under the site. The waves can be affected in such a way that when they reach the surface, they create more shaking. Macroseismic observations have demonstrated very clearly that the damaging effects associated with such soft deposits may lead to local intensity increments as large as 2, in extreme cases even 3 degrees on the MM (Modified Mercalli) or MSK/EMS (Medvedev, Sponheuer and Karnik ; 1964 scale) scale (Irikura 1983; Lacave, Bard et al. 2002). For the investigations of the soil site effects, the methods used are empirical, theoretical or semiempirical. For this research, widely used software (SHAKE2000) is applied and one-dimensional (horizontally layered) responses of soil layers are calculated using numerical methods. Finally, SHAKE2000 needs specific geotechnical inputs such as; input signal (scenario earthquake) shear wave velocity and soil thickness. The overall research problem is focused on analysing the sensitivity of these input parameters. For that, one of the parameters is kept constant and others vary in realistic values. Not so many sensitivity analyses have taken place for the general input parameters for ground response modelling so far in literature. Though, there is a great demand from engineers and planners to be able to conduct earthquake resistant buildings for high-risk areas. The outcome of the sensitivity analysis and the research provides range of values for the input parameters and their properties. The general terminology and the overall research concept have been introduced above. In the coming sections the various components will be treated more in detail. Different views and newly advised ideas will be presented in a short summary. 2.1. Overview Of Methods For Seismic Hazard Assessment 2.1.1. Seismic Hazard Assessment Seismic hazard analyses involve the quantitative estimation of ground shaking hazards at a particular site (Kramer 1996). On the other hand in the Global Seismic Hazard Assessment Program (1992- 1999), seismic hazard analyses were defined as “the assessment of seismic hazard measures our understanding of the recurrence of earthquakes in seismogenic sources” (Giardini 1999). Here, the probability of earthquakes was mentioned to be involved in the overall assessment. Occasionally, the division between the deterministic and the probabilistic studies still continues to take place in studies. Seismic hazard assessment could be deterministic or probabilistic; the two ways could also be used for one study. The decision is more depends on the approach and available data for the region. Initially, for the probabilistic approach (PSHA) first formed by Cornell (1968), the following procedures are applied. First, the delineation of earthquake source regions in terms of their boundaries, level of activity and upper intensity threshold are applied (Step 1 in the Figure 2-1). Second part is the determination of the macroseismic intensity changes with distance, magnitude, focal length and ground conditions (Step 2-3; Particularly in the direction from the source region to the site) Third, applications of a theoretical model to the calculation of the seismic hazard at the site under study (Step 4) (Schenk 1996). Sensitivity Analysis Of Soil Site Response Modelling In Seismic Microzonation For Lalitpur, Nepal 17
Page 1 and 2: Sensitivity Analysis of Soil Site R
Page 3 and 4: Disclaimer This document describes
Page 5 and 6: Abstract For a proper design of ear
Page 7 and 8: 6.4. Sensitivity for Unit Weight ..
Page 9 and 10: Figure 3-7 The display of results f
Page 11 and 12: List of Tables Table 1-1 Investigat
Page 13 and 14: 1. Introduction 1.1. Scope of the s
Page 15 and 16: Figure 1-2 The seismic hazard map o
Page 17 and 18: 1.3. Research Objectives Sensitivit
Page 19 and 20: Methodology A) Literature Review B)
Page 21 and 22: • Array method using ambient vibr
Page 23 and 24: Shear wave velocity Just like the o
Page 25 and 26: • Hard copy maps of the engineeri
Page 27: 6. Chapter six the assessment of th
Page 31 and 32: Figure 2-2 A probabilistic seismic
Page 33 and 34: Figure 2-4 The deterministic seismi
Page 35 and 36: create stronger shaking and make lo
Page 37 and 38: agreed on the method’s functional
Page 39 and 40: n = - e trans / e longitudinal Stra
Page 41 and 42: Several other studies have looked t
Page 43 and 44: the two approaches are not going to
Page 45 and 46: presence of heavy structures or sti
Page 47 and 48: other parameters are kept constant.
Page 49 and 50: Sensitivity Analysis Of Soil Site R
Page 51 and 52: In addition to the above-mentioned
Page 53 and 54: As mentioned by Ordonez (2002), the
Page 55 and 56: In the first option the dynamic soi
Page 57 and 58: The third option lets you to choose
Page 59: SHAKE 2000 METHODOLOGY MAIN MENU Cr
Page 62 and 63: Lalitpur is on the south of Kathman
Page 64 and 65: solidated sediments of the valley c
Page 66 and 67: 4.3. Seismicity Nepal is within the
Page 68 and 69: Figure 4-6 Map showing, seismic dat
Page 70 and 71: m. The numbers of blows are counted
Page 72 and 73: Figure 5-1 Map showing borehole loc
Page 74 and 75: For the other input parameter, stro
Page 76 and 77: and the third one is from real reco
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Scenario 1 Scenario 2 Scenario 3 PG
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7). Though the magnitude is great a
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B 23 - Analysis No. 1 - Profile No.
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used is Los Angeles, Magnitude: 6.2
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Soil Profile No. 1 - Analysis No. 1
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The soil profile is divided into fo
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the input data, all spatial calcula
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Table 5-10 The relations between th
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Methodology 2 Input and Output Rela
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Figure 5-16 The natural frequency m
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tween the inputs and outputs of the
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R 2 = 1- SSE SST SSE= ∑ (Yi-Ỳi
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6.3. Sensitivity to Input Motions T
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When the response spectra are consi
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Unit Weight (Kcf) 0,35 0,3 0,25 PGA
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PGA Values for Differing Depth Valu
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In order to give some range of valu
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Avouac, personal communication) and
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Based on the results of the sensiti
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• Using similar earthquake signal
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• IRIS, I. R. I. f. S. (2003). Se
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108 Sensitivity Analysis Of Soil Si
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Los Angeles Simulated strong ground
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Appendix B: Soil Profile Informatio
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medium to coarse Sand 2 5 16.4 18 1
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Clay 1 1 3.3 16 102 0.10 300 984 60
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6188 118 Sensitivity Analysis Of So
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26 0.29 1.15 1.85 1.31 0.93 27 0.2
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