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Ground Motions versus Geotechnical andStructural Damage in the February 2011Christchurch EarthquakeEleni Smyrou, Panagiota Tasiopoulou, İhsan Engin Bal, and George GazetasEleni Smyrou, 1 Panagiota Tasiopoulou, 1 İhsan Engin Bal, 2 and GeorgeGazetas 1INTRODUCTIONThe M w = 6.3 earthquake of February 22 was the strongest seismicevent in a series of damaging aftershocks in and aroundChristchurch after the Darfield earthquake on 4 September2010. The source of the Darfield earthquake was in a sparselypopulated area and thus it caused no loss of life. Serious damagewas mainly due to extensive liquefaction. By contrast, theChristchurch earthquake was generated on a fault in closeproximity to the city, resulting in a death toll of 181 people.The Canterbury Plains are covered with river gravels thathide any evidence of past fault activity in this region. The newlyrevealed Greendale fault was therefore completely unknown.Only a portion of it was revealed on the ground surface duringthe Darfield earthquake. The second fault (the one thatruptured in February 2011) appears to be a continuation of thefirst, although no fault structure directly connecting the faultshas been recognized. There is a debate among seismologists atthis point whether this is a different fault from Greendale oneor not (NHRP 2011a; NHRP 2011b; Geonet 2011).Due to its magnitude, shallow depth and close proximity tothe city, the February earthquake proved particularly destructivefor the central business district (CBD) of Christchurch,where buildings suffered extensive damage. Thanks to a densenetwork of strong ground motion stations, a large number ofrecords have been obtained, which provide valuable informationon the event and offer the possibility of relating the extentof damage to actual measurements of ground shaking.Apart from the southern part of the city on the hills andthe Lyttelton port area, Christchurch is built on deep estuarinesoil, which has been shaped in the last thousands of years by theever-changing riverbed. Fine sands—the dominant soil type—and the high ground water level contributed to widespreadliquefaction in one or both earthquake events. Often accompaniedby lateral spreading, liquefaction amplified the level ofdamage, resulting in the failure of structures in the CBD andsurrounding areas, as will be explained below.1. Soil Mechanics Laboratory, School of Civil Engineering, NationalTechnical University, Athens, Greece2. Fyfe Europe S.A. Athens, GreeceThe older buildings in the city center, many of which aremade of unreinforced masonry with timber floors, were mostlybuilt in the late 19th and early 20th century, following Englisharchitectural style and construction practice and with no considerationof the high seismicity of the region. However, someof these buildings had been retrofitted in recent years. In contrast,many of the modern buildings in the CBD were designedin accordance with recent seismic codes, although their foundationsystems were not always suitable for the adverse effectsstemming from liquefaction. Thus, despite the fact that liquefiedlayers beneath the CBD restricted somewhat the amplitudeof already significantly high accelerations, the increasedvelocities and displacements due to soil softening magnified thedemands on long-period structures. Both structural and geotechnicalaspects are investigated here in an effort to broadlyexplain and quantify the observed damage.THE STRONG MOTION RECORDSThanks to a dense network of seismographs covering the broaderarea of Christchurch (Figure 1), a large number of groundmotions were recorded during the Christchurch February2011 earthquake. The CBD area includes four seismic stations:CBGS, CCCC, REHS and CHHC. The first three records aretruly free-field motions. CHHC was located near the base of atwo-story building and its motion may reflect to some degreethe effect of the structure. These ground motions may not havebeen the strongest ones recorded in terms of PGA values; however,due to certain features, their effect on structures or soilswas detrimental.There is a certain variation in the recorded accelerationtime histories (Figure 1). For instance, the range of PGA valuesvaries within a factor of 2, from 0.34 g (CHHC-NS) to 0.72 g(REHS-EW). A dominant common feature in all records is thesign of liquefaction: long-period cycles with reduced accelerationamplitudes occurring after a threshold acceleration has beenreached. Soil softening due to excess pore water pressures in combinationwith sufficient acceleration values has led to amplificationof large periods affecting a broad category of structures, asindicated by the acceleration spectra. In particular, the spectral882 Seismological Research Letters Volume 82, Number 6 November/December 2011 doi: 10.1785/gssrl.82.6.882
(A)(B)(C)(D)(E)▲▲Figure 1. A) Map of the broader Christchurch area showing the intersection of the fault plane with the ground surface (from GNSScience), the location of the accelerograph stations, the epicenter of the Christchurch 2011 earthquake, and the location with availablesoil data. B–E) Acceleration time histories and spectra of four CBD (central business district) seismic stations for NS and EWdirections.Seismological Research Letters Volume 82, Number 6 November/December 2011 883
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Volume 82, Number 6 November/Decemb
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News and Notes (continued)Nominatio
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Preface to the Focused Issue on the
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TABLE 1Peak ground acceleration (PG
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▲▲Figure 2. A) Sketch of the
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▲▲Figure 4. A) Adopted moment r
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▲▲Figure 7. As in Figure 6 but
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▲ ▲ Figure 8. Misfit parameters
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▲ ▲ Figure 10. Spatial variabil
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▲ ▲ Figure 12. Standard spectra
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Quigley, M., R. Van Dissen, P. Vill
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slip on a 59-degree striking fault
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▲▲Figure 4. Convergence of inve
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observations and other source studi
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-42. 5-43. 0-43. 5-44. 0-44. 5-43.2
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“Product CSK © ASI, (ItalianSpac
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TABLE 2Solutions for fault location
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-43.45(A)degrees N-43.50-43.552.52.
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is still a good fit to the horizont
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Coulomb Stress Change Sensitivity d
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mation takes on a larger strike-sli
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P 9.4267BLDU45P 20.1213CASY39P 2.62
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ERMJNUMAJOINUJHJ2CBIJMIDWJOWYHNBTPU
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(A)6.146.13(B)6.246.36Misfit6.156.1
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(A)(B)(C)(D)▲▲Figure 10. The co
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(A)(B)(C)(D)▲▲Figure 12. The co
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Luo, Y., Y. Tan, S. Wei, D. Helmber
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−44˚00' −43˚00'4-Sep-2010Mw 7
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TABLE 1Pairs of SAR imagery used in
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Depth (km)Coulomb Stress Change(bar
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Crippen, R. E. (1992). Measurement
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AlpineFaultHope Fault38 mm/yr0+ +-1
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σ 1dσ 3Nuσ 3CM w 7.1dw 6.2u70°M
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Right-lateral Faults(A) Range Front
Page 77 and 78: DISCUSSIONThe 2010-2011 Canterbury
Page 79 and 80: Large Apparent Stresses from the Ca
Page 81 and 82: ▲ ▲ Figure 2. Observed vs. pred
Page 83 and 84: 10Obs SA(1s)AS1AS+SDAB 2006AB+SDSA(
Page 85 and 86: Fine-scale Relocation of Aftershock
Page 87 and 88: −43.25°OXZ0 10 20km−43.5°−4
Page 89 and 90: A’0 km 4 8−43.5°B’B−43.6°
Page 91 and 92: REFERENCESAvery, H. R., J. B. Berri
Page 93 and 94: ▲ ▲ Figure 2. A) shows three-co
Page 95 and 96: ▲ ▲ Figure 4. Vertical accelera
Page 97 and 98: 0.8PRPC Z0.40Normalized (Max PGA +
Page 99 and 100: Near-source Strong Ground MotionsOb
Page 101 and 102: (A)Magnitude, M w876542009 NZdataba
Page 103 and 104: Scale0.5 g5 seconds▲▲Figure 4.
Page 105 and 106: (A)(B)Spectral Acc, Sa (g)North/Wes
Page 107 and 108: Vertical-to-horizontal PGA ratio543
Page 109 and 110: (A)(B)Station:CCCCSolid:AvgHorizDas
Page 111 and 112: REFERENCESAagaard, B. T., J. F. Hal
Page 113 and 114: ▲ ▲ Figure 1. Shear-wave veloci
Page 115 and 116: Spectral Acceleration (0.3 s), (g)I
Page 117 and 118: Spectral Acceleration (3 s), (g)In[
Page 119 and 120: TABLE 1Mean (μ LLH ) and standard
Page 121 and 122: Strong Ground Motions and Damage Co
Page 123 and 124: ings and the Modified Takeda-Slip M
Page 125 and 126: high, but there were no buildings d
Page 127: REFERENCES▲▲Figure 8. Heavily d
Page 131 and 132: (A) (B) (C)▲ ▲ Figure 3. A) Typ
Page 133 and 134: (A) (B) (C)▲ ▲ Figure 4. A) Typ
Page 135 and 136: Case StudyKey ParametersTABLE 1Key
Page 137 and 138: ▲ ▲ Figure 9. Representative bu
Page 139 and 140: Soil Liquefaction Effects in the Ce
Page 141 and 142: ▲ ▲ Figure 2. Representative su
Page 143 and 144: Location of structures illustrated
Page 145 and 146: Shading indicates areaover which pr
Page 147 and 148: 1.8 deg15 cmGround cracking due to
Page 149 and 150: 30 cm17 cm30 cmFoundation beam▲
Page 151 and 152: Comparison of Liquefaction Features
Page 153 and 154: (A)(B)▲▲Figure 2. A) Simplified
Page 155 and 156: (A)Acceleration (Gal)6004002000-200
Page 157 and 158: (A)(B)▲▲Figure 7. Distribution
Page 159 and 160: (A)(B)▲▲Figure 10. Damage to a
Page 161 and 162: (A)(B)▲ ▲ Figure 14. A) Subside
Page 163 and 164: ▲▲Figure 17. A trench in a resi
Page 165 and 166: Ambient Noise Measurements followin
Page 167 and 168: ▲▲Figure 1. Location of the noi
Page 169 and 170: ▲▲Figure 5. Site N20 showing HV
Page 171 and 172: ▲▲Figure 8. Comparison between
Page 173 and 174: Use of DCP and SASW Tests to Evalua
Page 175 and 176: ▲ ▲ Figure 2. Aerial image of C
Page 177 and 178: (A)(B)▲▲Figure 4. DCP test bein
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▲▲Figure 7. SASW setup at a sit
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where X ~ N(μ X , σ X 2 ) is shor
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Using the same critical layers as s
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Performance of Levees (Stopbanks) d
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▲▲Figure 3. Typical geometry an
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TABLE 1Damage severity categories (
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(A)(B)▲▲Figure 6. A) Large sand
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(A)(B)▲▲Figure 8. A) Representa
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each of the Waimakariri River and a
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▲ ▲ Figure 2. Horizontal peak g
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only minor damage, mostly to their
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(A)(C)(B)▲▲Figure 5. Ferrymead
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(A)(B)▲▲Figure 7. Damage to sou
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(A)(B)▲▲Figure 11. Settlement o
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(A)(C)(B)▲▲Figure 14. Railway B
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Events Reconnaissance (GEER) Associ
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New PublicationsCanGeoRefThe Americ
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Wednesday, 18 AprilTechnical Sessio
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Verification of a Spectral-Element
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EASTERN SECTIONRESEARCH LETTERSReas
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(A)70°N100°W 60°W70°N(B)100°E1
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Mongolia SCRThe presence or absence
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the small horizontal relative motio
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80°100°120°140°EXPLANATIONBorde
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Chang, K. H. (1997). Korean peninsu
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Wheeler, R. L. (2008). Paleoseismic
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A significant outcome of this study
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TABLE 1 (continued)Earthquakes for
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▲▲Figure 2. Earthquakes used in
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Meeting CalendarM E E T I N GC A L
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201 Plaza Professional Bldg. • El
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Seismological Research Letters (SRL
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Christa von Hillebrandt-Andrade, Pr
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