Here - Stuff

More documents

Recommendations

Info

Coulomb Stress Change Sensitivity due toVariability in Mainshock Source Models andReceiving Fault Parameters: A Case Study ofthe 2010–2011 Christchurch, New Zealand,EarthquakesZhongwen Zhan, Bikai Jin, Shengji Wei, and Robert W. GravesZhongwen Zhan, 1,2 Bikai Jin, 3 Shengji Wei, 1 and Robert W. Graves 4INTRODUCTIONStrong aftershocks following major earthquakes present significantchallenges for infrastructure recovery as well as for emergencyrescue efforts. A tragic instance of this is the 22 February2011 M w 6.3 Christchurch aftershock in New Zealand, whichcaused more than 100 deaths while the 2010 M w 7.1 Canterburymainshock did not cause a single fatality (Figure 1). Therefore,substantial efforts have been directed toward understandingthe generation mechanisms of aftershocks as well as mitigatinghazards due to aftershocks. Among these efforts are the predictionof strong aftershocks, earthquake early warning, and aftershockprobability assessment. Zhang et al. (1999) reported asuccessful case of strong aftershock prediction with precursorydata such as changes in seismicity pattern, variation of b-value,and geomagnetic anomalies. However, official reports of suchsuccessful predictions in geophysical journals are extremelyrare, implying that deterministic prediction of potentiallydamaging aftershocks is not necessarily more scientifically feasiblethan prediction of mainshocks.A potentially more effective approach for aftershock hazardmitigation is described by Bakun et al. (1994) for the caseof the Loma Prieta earthquake. This approach relies on therapid detection of an aftershock using a dense observationnetwork in the rupture area of the mainshock and subsequentbroadcast of an alert to more distant sites. Recent progress inrapid determination of epicenter and magnitude involving a1. Seismological Laboratory, California Institute of Technology,Pasadena, California 91125 U.S.A.2. Mengcheng National Geophysical Observatory, School of Earthand Space Sciences, University of Science and Technology of China,Hefei 230026 China3. Key Laboratory of Dynamic Geodesy, Institute of Geodesy andGeophysics, Chinese Academy of Sciences, Wuhan 430077 China4. U.S. Geological Survey, 525 South Wilson Avenue, Pasadena,California, 91106 U.S.A.small number of stations and short time window of P waveforms(Allen and Kanamori 2003; Wan et al. 2009; Wang etal. 2009) make the approach of earthquake early warning moreeffective for regions not very close to the rupture area of themainshock. Such an approach might have been useful for aftershocksof the 2008 Wenchuan earthquake, where megacitiessuch as Chengdu are about 90 km away and 20 seconds wereavailable for rapid mitigation response. But in the case of the2011 Christchurch earthquake, the populated region is onlyabout 10 km from the epicenter, thus leaving little time forearly warning.For a situation such as Christchurch, aftershock probabilityassessment may provide a viable approach to address thehazard level. Several aftershock-triggering mechanisms, i.e., thestatic Coulomb stress theory (King et al. 1994; Stein 1999),the dynamic triggering theory (Felzer and Brodsky 2006),and viscoelastic relaxation theory (Freed et al. 2001), can beapplied to assess aftershock probabilities. In this paper we willconcentrate on how applicable the static Coulomb stress triggeringmechanism is to the 2011 Christchurch aftershock andexamine the sensitivity of the stress changes to mainshock slipdistribution and aftershock fault orientation. The Coulombstress theory has been broadly applied in aftershock studies(e.g., King et al. 1994; Parsons et al. 1999; Toda et al. 1998; Maet al. 2005), earthquake sequencing (Stein et al. 1997; Xionget al. 2010; Nalbant et al. 1998) and the triggering of large tomoderate earthquakes (Parsons et al. 2000). Previous studies(e.g., Harris 1998, 2000; Freed 2004; King et al. 1994; Stein1999) proposed a Coulomb stress change of 0.01 MPa to be thethreshold for potential earthquake triggering.The Coulomb stress triggering theory involves computingthe change in normal traction and shear traction on a fault(receiving fault) caused by changes of the stress field due to themainshock. Therefore, accurate information on the receivingfault geometry (strike, dip, rake, and focal depth) and sourcemodel of the mainshock are necessary for effective assessment800 Seismological Research Letters Volume 82, Number 6 November/December 2011 doi: 10.1785/gssrl.82.6.800
43.25˚S0 5 10 15 200 5 10 15 20M3 M5 M7depth(km)depth(km)GCMT/Mw7.0CAP/Mw6.343.5˚S43.75˚Skm0 10 20171.75˚E 172˚E 172.25˚E 172.5˚E 172.75˚E▲ ▲ Figure 1. Seismicity in the first three days after the 2010 Canterbury mainshock (color-scaled dots) and the 2011 Christchurchaftershock (dots in gray scale). The red lines are the free surface rupture trace from field observation. The big red star indicates theepicenter of the main event and the smaller red star is the location of the M w 6.3 aftershock. The GCMT solution of mainshock and thecut-and-paste (CAP) mechanism of the aftershock are shown as beach balls. The black rectangles are the free surface projection ofthe two-segment model, which are used in the teleseismic finite fault inversion. The yellow rectangles are for the four-segment modelused in the stochastic slip model.of aftershock probability. Due to inadequate coverage of seismicand geodetic observation systems and inaccurate 3D Earthstructure models, there are always errors in the source modelsof the mainshock. Moreover, fault geometries of future aftershocksare not precisely known, and aftershocks occurring onblind faults are particularly difficult to study due to lack ofgeological information about the faults. For example, the 1994Northridge earthquake occurred on a blind (buried) fault;the study of its potential triggering by the 1971 San Fernandoearthquake was only made possible after its rupture plane andhypocenter depth were resolved (Stein et al. 1994). The 2011Christchurch earthquake was another case of such a blindearthquake, which has not yet been associated with any knowngeological faults. Thus, this event is a valuable case study of howeffective the Coulomb stress mechanism is in triggering aftershocks,and its variability due to the uncertainties in receivingfault parameters and mainshock source models.In this paper we examine the sensitivity of computed staticCoulomb stress change levels to source parameterization byconsidering various combinations of mainshock rupture modelsand aftershock fault orientations for the 2010 Canterburyand 2011 Christchurch earthquakes. General constraints onthe mainshock source models and aftershock fault geometryare provided by teleseismic and geodetic data. We also investigatethe sensitivity of the results to aftershock focal depth andapparent coefficient of friction. We conclude with a discussionof how these results can be used in combination with focalmechanism studies to help constrain aftershock rupture assessmentusing Coulomb stress change calculations.GENERAL INFORMATION ON THE M w 7.1CANTERBURY EARTHQUAKE AND THE M w 6.3CHRISTCHURCH EARTHQUAKEThe Australian and Pacific plates converge obliquely at about40 mm yr −1 at New Zealand. Partly due to along-strike variationsin the orientations of both the plate boundary and thedirection of relative motion between the plates, the defor-Seismological Research Letters Volume 82, Number 6 November/December 2011 801
Page 1: Volume 82, Number 6 November/Decemb
Page 7: News and Notes (continued)Nominatio
Page 11: Preface to the Focused Issue on the
Page 14 and 15: TABLE 1Peak ground acceleration (PG
Page 16 and 17: ▲▲Figure 2. A) Sketch of the
Page 18 and 19: ▲▲Figure 4. A) Adopted moment r
Page 20 and 21: ▲▲Figure 7. As in Figure 6 but
Page 22 and 23: ▲ ▲ Figure 8. Misfit parameters
Page 24 and 25: ▲ ▲ Figure 10. Spatial variabil
Page 26 and 27: ▲ ▲ Figure 12. Standard spectra
Page 28 and 29: Quigley, M., R. Van Dissen, P. Vill
Page 30 and 31: slip on a 59-degree striking fault
Page 32 and 33: ▲▲Figure 4. Convergence of inve
Page 34 and 35: observations and other source studi
Page 36 and 37: -42. 5-43. 0-43. 5-44. 0-44. 5-43.2
Page 38 and 39: “Product CSK © ASI, (ItalianSpac
Page 40 and 41: TABLE 2Solutions for fault location
Page 42 and 43: -43.45(A)degrees N-43.50-43.552.52.
Page 44 and 45: is still a good fit to the horizont
Page 48 and 49: mation takes on a larger strike-sli
Page 50 and 51: P 9.4267BLDU45P 20.1213CASY39P 2.62
Page 52 and 53: ERMJNUMAJOINUJHJ2CBIJMIDWJOWYHNBTPU
Page 54 and 55: (A)6.146.13(B)6.246.36Misfit6.156.1
Page 56 and 57: (A)(B)(C)(D)▲▲Figure 10. The co
Page 58 and 59: (A)(B)(C)(D)▲▲Figure 12. The co
Page 60 and 61: Luo, Y., Y. Tan, S. Wei, D. Helmber
Page 62 and 63: −44˚00' −43˚00'4-Sep-2010Mw 7
Page 64 and 65: TABLE 1Pairs of SAR imagery used in
Page 67 and 68: Depth (km)Coulomb Stress Change(bar
Page 69 and 70: Crippen, R. E. (1992). Measurement
Page 71 and 72: AlpineFaultHope Fault38 mm/yr0+ +-1
Page 73 and 74: σ 1dσ 3Nuσ 3CM w 7.1dw 6.2u70°M
Page 75 and 76: 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 and 128:
REFERENCES▲▲Figure 8. Heavily d
Page 129 and 130:
(A)(B)(C)(D)(E)▲▲Figure 1. A) M
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
Page 179 and 180:
▲▲Figure 7. SASW setup at a sit
Page 181 and 182:
where X ~ N(μ X , σ X 2 ) is shor
Page 183 and 184:
Using the same critical layers as s
Page 185 and 186:
Performance of Levees (Stopbanks) d
Page 187 and 188:
▲▲Figure 3. Typical geometry an
Page 189 and 190:
TABLE 1Damage severity categories (
Page 191 and 192:
(A)(B)▲▲Figure 6. A) Large sand
Page 193 and 194:
(A)(B)▲▲Figure 8. A) Representa
Page 195 and 196:
each of the Waimakariri River and a
Page 197 and 198:
▲ ▲ Figure 2. Horizontal peak g
Page 199 and 200:
only minor damage, mostly to their
Page 201 and 202:
(A)(C)(B)▲▲Figure 5. Ferrymead
Page 203 and 204:
(A)(B)▲▲Figure 7. Damage to sou
Page 205 and 206:
(A)(B)▲▲Figure 11. Settlement o
Page 207 and 208:
(A)(C)(B)▲▲Figure 14. Railway B
Page 209 and 210:
Events Reconnaissance (GEER) Associ
Page 211 and 212:
New PublicationsCanGeoRefThe Americ
Page 213 and 214:
Wednesday, 18 AprilTechnical Sessio
Page 215 and 216:
Verification of a Spectral-Element
Page 217 and 218:
EASTERN SECTIONRESEARCH LETTERSReas
Page 219 and 220:
(A)70°N100°W 60°W70°N(B)100°E1
Page 221 and 222:
Mongolia SCRThe presence or absence
Page 223 and 224:
the small horizontal relative motio
Page 225 and 226:
80°100°120°140°EXPLANATIONBorde
Page 227 and 228:
Chang, K. H. (1997). Korean peninsu
Page 229 and 230:
Wheeler, R. L. (2008). Paleoseismic
Page 231 and 232:
A significant outcome of this study
Page 233 and 234:
TABLE 1 (continued)Earthquakes for
Page 235 and 236:
▲▲Figure 2. Earthquakes used in
Page 237 and 238:
Meeting CalendarM E E T I N GC A L
Page 239 and 240:
201 Plaza Professional Bldg. • El
Page 241 and 242:
Seismological Research Letters (SRL
Page 243 and 244:
Christa von Hillebrandt-Andrade, Pr
show all

Here - Stuff

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?