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slip on a 59-degree striking fault plane. Their solution is alsovery similar to the regional moment tensor solution of strike/dip/rake: 55/66/129 (Sibson et al. 2011, page 824 of thisissue). We constrained the fault plane location using the relocatedhypocenter of Bannister et al. 2011 (page 839 of thisissue) of latitude –43.571, longitude 172.703, and 6 km depth.The geometry of the fault plane is fixed, but the rupture isallowed to start anywhere on the fault plane. We didn’t constrainthe rupture to start at the hypocenter since we are invertingfor the time history of the low-frequency source of energyrelease, which can have a different origin time location thanthe hypocenter. In order to account for delays in the onset ofthe main slip patch, the slip distribution is independent of thestarting time. The modeled fault plane dimensions are 20 × 20km discretized into 400 1 × 1 km 2 subfaults. We invert for anelliptical distribution of slip on the fault plane (Di Carli et al.2010) described by nine parameters: the size (two semi-axislengths) and location (along strike and along dip) of the ellipse,location of rupture starting time (along strike and along dip),rake, maximum slip, and rupture velocity.Synthetic seismograms were computed using the discretewavenumber approach of Bouchon (1981), using the 1D velocitymodel from Reyners and Cowan (1993).To search for a minimum waveform misfit, we used thenon-linear Neighborhood Algorithm (Sambridge 1999). Themisfit function is a least-squares scheme applied to the first 10seconds of the recordings. The 10-second window is justifiedby the short rupture time of this moderate-size earthquakeand the proximity of the stations (less than 20 km). The followingsearch parameters are empirically based on many yearsof experience using the neighborhood algorithm for kinematicinversion purposes. In this study the parameters are tuned tobe more exploitative than explorative (Sambridge 1999). Theinversion scheme first computes 400 models then runs 600iterations. For each iteration, the algorithm computes 12 modelsand selects the four models with the lowest misfit to definethe parameter search for the next iteration.RESULTS: SOURCE MODELSA total of 7,600 models were computed during the inversion.Our final slip distribution is shown in Figure 2. The inversionprocedure has converged clearly (Figure 3) to a final misfitvalue of 45.1458. Each individual parameter has also convergedsharply, and the differences between the final values and valuesof the last 1,000 computed models are negligible as seenon Figure 4. The misfit value for model 6530 (iteration 511) is45.1476.The waveform fit is overall very good (Figure 5). All threeonset, amplitude, and polarities criteria are well-matched. Thematch is even better for vertical components, showing fewercomplexities than the horizontal components, where we alsofit the first wave envelopes of the synthetic and observed seismograms.The final slip distribution parameters are shown on Figure1 and Figure 2 and described in Table 1. The rupture is characterizedby a high rupture velocity of 2.8 km/s and a maximumslip value of 4.2 m. The maximum slip is located at about 4 kmdepth; there is still up to 1.5 m slip at 500 m depth. The rupturearea is 12 by 18 km 2 . The total rupture duration is less than4 seconds. The rake angle is 135 degrees. The direction of therupture is nearly vertical, oriented toward Christchurch, hencecontributing to the extreme ground shaking experienced inChristchurch city.DISCUSSIONThis proposed kinematic model shows consistent locationof a slip patch right below the Avon River estuary, depthrange (maximum slip around 4 km depth), and moment of3.46 × 10 18 Nm to the model obtained by Beavan et al. 2011(Mo 3.13 × 10 18 Nm) (page 789 of this issue). However, intheir one-fault model, Beavan et al. obtained a smaller maximumslip amplitude (2.5 m), although this value can increase bychanging the smoothing parameter in their inversion (Beavan,personal communication 2011). Our rake angle of 135 degreesshows a larger reverse component than their value of 154degrees; however, the rake angle of their main fault decreasesif they introduce a secondary strike-slip source. Our solution isvery close to the regional moment tensor solution of strike/dip/rake 55/66/129 (Mo 2.49 × 10 18 Nm) (Sibson et al. 2011, page824 of this issue).The proposed kinematic model is characterized by highrupture parameter values for an earthquake of its size such ashigh rupture velocity (2.8 km/s) and very large slip (maximum4.2 m), suggesting that this was a high stress drop event. Thehigh rupture velocity is also noted in Fry et al. 2011, page 833of this issue; based on data filtered up to 5 Hz, their modelrequires a rupture velocity of 3.2 km/s in order to reproducethe very high accelerations observed near source. Finally, thelarge difference between the energy magnitude of 6.7 (USGS)for this earthquake versus the M w magnitude of 6.2 supportsthe possibility of this event being a high stress drop event (Fryand Gerstenberger 2011, page 833 of this issue).Similar to the Darfield Mw 7.1 event, geodetic studies andseismic data observations of the February earthquake suggestthat this is a segmented event. First, geodetic studies (Beavanet al. 2011, page 789 of this issue) suggest that a secondstrike-slip source (strike/dip/rake 80/90/180) of magnitudeM w 5.9 was involved in the rupture process. However they arenot able to assign a chronology to the two events. Then, thefocal mechanism solution using first motions analysis of theraw data (B. Fry, personal communication 2011) indicates analmost pure right-lateral strike-slip mechanism (strike/dip/rake 95/75/180), strongly suggesting that the February earthquakestarted on a small strike-slip patch and then ruptureda larger oblique-reverse slip patch. Finally, the waveform dataused in the present kinematic inversion (Figure 5) show a dominantpeak, even larger on the horizontal components, cominga few seconds after the main rupture and prior to the 3-secondresonant site effect for the soft site stations (the 3-second siteeffect was observed also in the Darfield earthquake by Cousins784 Seismological Research Letters Volume 82, Number 6 November/December 2011
▲▲Figure 1. Final slip distribution on a plane oriented 59 o strike and 67 o dip. Only the non-zero slip patches are shown here. The reddots are relocated aftershocks from Bannister et al. (2011, this issue) up until 29 May 2011. The light gray region represents the areaof Christchurch city. The stations named xxxC belong to the regional CanNet strong motion network of GeoNet; others are GeoNetnational strong motion stations. Stations used for the inversions are in bold straight letters. The slip distribution is characterizedhere by a patch of maximum 4.2 m slip occurring north and up-dip of the relocated hypocenter (yellow star). Banks Peninsula volcanoextends from just south of HVSC and beyond MQZ.▲▲Figure 2. Slip and rake history for the fault plane orientedstrike 59 o , dip 67 o . Slip is shown in color, and the rake is representedby black vectors for each grid cell. Distances are inkilometers and rupture time iso-contours are in seconds. Theyellow star is the relocated hypocenter from Bannister et al.(2011, this issue).▲ ▲ Figure 3. Convergence of the inversion scheme after 600 iterations.Each iteration computes a waveform misfit value for 12models; a total of 7,600 models have been computed.Seismological Research Letters Volume 82, Number 6 November/December 2011 785
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 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 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
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▲ ▲ Figure 2. Observed vs. pred
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10Obs SA(1s)AS1AS+SDAB 2006AB+SDSA(
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Fine-scale Relocation of Aftershock
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−43.25°OXZ0 10 20km−43.5°−4
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A’0 km 4 8−43.5°B’B−43.6°
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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
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Christa von Hillebrandt-Andrade, Pr
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