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(A)6.146.13(B)6.246.36Misfit6.156.186.656.196.466.206.236.396.266.256.276.296.34Misfit6.34 6.306.286.310 2 4 6 8 10 12 14Depth (km)1 2 3 4 5 6 7 8 9Duration (s)▲▲Figure 8. Misfit of teleseismic waveforms as a function of earthquake focal depth and duration. The best fitting focal mechanismsand magnitudes are also plotted to show the trade-offs between them.LayerTABLE 1Multilayered lithosphere model from CRUST 2.0.Thickness(km)V p(km·s –1 )Vs(km·s –1 )Density(kg·m –3 )Upper crust 14.3 6.0 3.5 2700Middle crust 9 6.6 3.7 2900Lower crust 11 7.2 4.0 3050Mantle 8.0 4.6 3300Effect of Focal Depth on Coulomb Stress ChangeThe sensitivity of our results to focal depth of the 2011Christchurch earthquake is explored by comparing the Δσ f distributionsresolved at depths of 2, 5, 10, and 15 km. Here thefocal depth is meant to be hypocentral depth, where ruptureof the Christchurch earthquake initiated. The depth inferredfrom waveform inversion is essentially centroid depth, and thehypocentral depth is typically difficult to resolve unless witha dense local seismic network. For these calculations, we usethe two-segment slip model of the mainshock along with thefocal mechanism of the receiving fault (52°/61°/128°) derivedfrom the teleCAP inversion. The results are shown in Figure10. Some local changes of the Δσ f distribution are observedin the far field, and complex changes happen in the near field.For example, the area with positive Δσ f at the east end of theGreendale fault is getting smaller when focal depth increases;and in the area of the mainshock thrust fault segment, Δσ fchanges polarity as the depth increases. The Δσ f at the 2011Christchurch earthquake epicenter are 0.035, 0.044, 0.065, and0.094 MPa at 2, 5, 10, and 15 km depth, respectively, increasingwith the depth and all above 0.01 MPa. Similar results areobtained for the other slip models, as shown in Table 2.Effect of Receiving Fault Geometry on Coulomb StressChangeTo analyze the impact of receiving fault geometry on the Δσ f ,we make some significant changes in the strike and dip of thereceiver fault (from focal mechanism) and compare their influenceon the resulting Δσ f distributions. The two-segment slipmodel of the mainshock and a focal depth of 5 km are adoptedin this calculation, and the results are shown in Figures 11(strike sensitivity) and 12 (dip sensitivity). In Figure 11, significantchanges in the Δσ f distribution can be observed as thestrike varies. When the strike of the receiving fault is rotatedcounterclockwise by 30 degrees, the area with positive Δσ fincreases in the near- and far-fields, compared with Figure 10.The opposite situation occurs when the strike of the receivingfault is rotated clockwise from the teleCAP solution. Similarchanges are also obtained when the dip angle of the receivingfault is changed by ± 20 degrees, as shown in Figure 12.The area with positive Δσ f outside the northwest corner ofthe Greendale fault grows with increasing dip angle. In thenear-field, the situation is a little more complex, but the wholeregion with positive Δσ f gets larger. From these two figures, weconclude that the Δσ f distribution can be quite sensitive to theassumed geometry of the receiving fault.Sensitivity of Coulomb Stress Change to Coefficient ofFrictionThe selection of an appropriate value for the apparent coefficientof friction μ′ is important because it controls the con-808 Seismological Research Letters Volume 82, Number 6 November/December 2011