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TABLE 2Solutions for fault location, geometry and slipUniform-slip, GPS only One fault Two faults, GPS+SARParameter 1σ uncert. GPS+SAR Plane 1 Plane 2lat –43.541° 0.1 km –43.545° –43.535° –43.575°lon 172.691° 0.2 km 172.690° 172.711° 176.666°strike 56° 1° 59° 58° 79.5°dip 61° 1° 66.5° 72° 87°rake 147° 2° see Fig. 5 see Fig. 6 see Fig. 6length 10.6 km 0.2 km 16 km 12 km 8 kmtop depth 1.4 km 0.1 km 1 km 1 km 2 kmwidth 5.3 km fixed 7 km 7 km 6 kmslip 2.1 m 0.1 m see Fig. 5 see Fig. 6 see Fig. 6M W 6.35 6.3 6.25 5.95Uniform-slip GPS-only solution has bottom depth of fault fixed at 6 km in this model.Lat and lon are the center of the fault trace if the fault plane were extended to the ground surface.M W calculated assuming 3 × 10 10 Nm –2 rigidity.Formal 1s uncertainties for the uniform-slip solution were calculated using the method recommended by the authors of thenon-linear least squares algorithm used by Darby and Beavan (2001).rectangular fault plane in an elastic half-space, using the GPSdata only (because disloc99 has not been modified to includeDInSAR data). We found that it was necessary to constrainonly the lower depth of faulting to obtain a solution for theother eight parameters describing the fault. Several sites,all in the eastern suburbs of Christchurch and other placeswhere ground damage was prevalent, had very large residuals.We increased the estimated uncertainties on these dataand repeated the inversion to give the solution in Table 2. Ifwe fix the bottom depth to different values we find a strongtrade-off between fault width and slip magnitude, but thecentroid depth is well constrained by the modeling at about3.5 km (i.e., if the bottom depth is fixed shallower, the solutionsfor top depth and slip magnitude are deeper and larger,respectively). The inferred M W is about 0.1 higher than seismologicalestimates (J. Ristau, personal communication 2011;see also Sibson et al. 2011, page 824 of this issue), but thisis not surprising given that deformation due to aftershocks isincluded in the geodetic solution.We extended the uniform-slip fault plane a few km inall directions and did a linear inversion for slip on this faultplane using both the GPS and DInSAR data, again assumingan elastic half-space model. We used inversion software basedon Jónsson et al. (2002) as described by Beavan, Samsonov,Denys, et al. (2010), solving for a linear ramp on each of theDInSAR datasets. We then did a grid search in the vicinity ofthis solution, varying the location, strike, and dip of the faultand repeating the inversion at each step to find the lowest χ 2solution. Some of the GPS data previously marked as outlierswere now reasonably good fits to the resulting model, sowe restored their original uncertainty values and repeated theinversion and grid search. The resulting fault location and slipdistribution are shown in Figures 5 and S5, the fault parametersare given in Table 2, and the slip solution is tabulated inTable S2. The fault runs from near Cashmere (Figure 1C) at itssouthwest end toward the Avon-Heathcote estuary and a fewkilometers offshore, with a strike of 59° and a dip of 66.5° to thesoutheast, a little steeper than in the uniform-slip, GPS-onlysolution. The main patch of slip, with maximum magnitude~2.5 m, is centered at a depth of ~4 km beneath the estuaryand is a mix of reverse faulting and right-lateral strike slip. Theslip on the southwestern part of the fault, with a maximummagnitude of ~1 m, is predominantly right-lateral strike slip.A preliminary, but very similar, version of this model using asubset of the data was published by Kaiser et al. (2011).Two-fault ModelThree observations suggest that a model consisting of morethan one fault might provide a significantly improved fit to theobservations: 1) the presence of a distinct lineation of smallaftershocks (Bannister et al. 2011, page 839 of this issue) tothe south of the inferred fault plane; 2) the location of twomajor aftershocks near the west end of this lineation; and 3)the pattern of misfits to some of the GPS data. We tried atwo-fault model with one plane coincident with the one-faultmodel and another coincident with the aftershock lineation,then did a grid search varying the location and geometry ofthe faults and solving for the slip distribution at each step. Theminimum misfit solution is shown in Figures 6 and S6, parametersfor both planes are listed in Table 2, and the full solutionis tabulated in Table S3. Again, some sites previously markedas misfits were now in good agreement with the model so wereturned their uncertainties to their original values before thefinal inversion run; it is this final set of uncertainties that isgiven in Table S1. In this solution the southern fault plane isclosely coincident with the aftershock lineation and with the794 Seismological Research Letters Volume 82, Number 6 November/December 2011
-43.45(A)degrees N-43.50-43.552.52.01.51.00.50.0Fault slip, mupper edge-43.60200 mm observed200 mm modelled172.55172.60172.65 172.70degrees E172.75172.80distance down dip, km02468(B)2.5 m2. 52. 01. 51. 00. 50. 0Slip, m0510 15 20SW distance along strike, km NE▲ ▲ Figure 5. A) Locations of model fault and its slip magnitude (colored rectangles) assuming a single planar fault, GPS displacementsobserved (blue arrows) and modeled (red arrows), and aftershocks since September 2010 (crosses). Central Christchurch shown bysolid black square. B) Slip distribution of hanging wall relative to footwall on model fault plane. Red-and-white four-pointed stars showlocations of mainshock on 22 February and (in A) the two major aftershocks to its southwest a few hours later.estimated hypocentral locations and focal planes of the twomajor aftershocks (S. Bannister, J. Ristau, personal communication2011; see also Sibson et al. 2011, page 824 this issue).The estimated M W is also close to that estimated seismologicallyfor the aftershocks. The mainshock plane is somewhatsteeper than in the single-fault solution, and the slip patch ismore concentrated. By changing the degree of smoothing inthe inversion the maximum slip can vary from less than 2.5 mto over 3 m, but the moment is stable.We perform an F-test to determine whether the two-faultsolution is significantly better than the one-fault solution. Theweighted residual sum of squares, number of data, and numberof parameters are 8,210, 1,657, 231 (one fault), and 5,400,1,657, 278 (two faults). These values give a tiny probability thatthe two models fit the data equally well. However, the truenumber of parameters is overestimated due to smoothing ofthe solution so this result is not definitive.Consistency of the DatasetsWe investigate the consistency of the datasets by re-running thesolution with different weightings for the GPS and DInSARdata sets. If the DInSAR data are strongly downweighted (i.e.,effectively a GPS-only solution), the location of maximum slipshallows by about 0.5 km but there is little other change. IfSeismological Research Letters Volume 82, Number 6 November/December 2011 795
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 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 46 and 47: Coulomb Stress Change Sensitivity d
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
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▲ ▲ Figure 2. A) shows three-co
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▲ ▲ Figure 4. Vertical accelera
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0.8PRPC Z0.40Normalized (Max PGA +
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Near-source Strong Ground MotionsOb
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(A)Magnitude, M w876542009 NZdataba
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Scale0.5 g5 seconds▲▲Figure 4.
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(A)(B)Spectral Acc, Sa (g)North/Wes
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Vertical-to-horizontal PGA ratio543
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(A)(B)Station:CCCCSolid:AvgHorizDas
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REFERENCESAagaard, B. T., J. F. Hal
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▲ ▲ Figure 1. Shear-wave veloci
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Spectral Acceleration (0.3 s), (g)I
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Spectral Acceleration (3 s), (g)In[
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TABLE 1Mean (μ LLH ) and standard
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Strong Ground Motions and Damage Co
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ings and the Modified Takeda-Slip M
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high, but there were no buildings d
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REFERENCES▲▲Figure 8. Heavily d
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(A)(B)(C)(D)(E)▲▲Figure 1. A) M
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(A) (B) (C)▲ ▲ Figure 3. A) Typ
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(A) (B) (C)▲ ▲ Figure 4. A) Typ
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Case StudyKey ParametersTABLE 1Key
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▲ ▲ Figure 9. Representative bu
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Soil Liquefaction Effects in the Ce
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▲ ▲ Figure 2. Representative su
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Location of structures illustrated
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Shading indicates areaover which pr
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1.8 deg15 cmGround cracking due to
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30 cm17 cm30 cmFoundation beam▲
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Comparison of Liquefaction Features
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(A)(B)▲▲Figure 2. A) Simplified
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(A)Acceleration (Gal)6004002000-200
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(A)(B)▲▲Figure 7. Distribution
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(A)(B)▲▲Figure 10. Damage to a
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(A)(B)▲ ▲ Figure 14. A) Subside
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▲▲Figure 17. A trench in a resi
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Ambient Noise Measurements followin
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▲▲Figure 1. Location of the noi
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▲▲Figure 5. Site N20 showing HV
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▲▲Figure 8. Comparison between
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Use of DCP and SASW Tests to Evalua
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▲ ▲ Figure 2. Aerial image of C
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(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
Page 243 and 244:
Christa von Hillebrandt-Andrade, Pr
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