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摘要:
模拟2015年尼泊尔地震（主震MW7.8及最大余震MW7.3）GPS/InSAR同震位移、远震体波、高频GPS位移波形和强震加速度记录，构建统一震源模型.统一模型分布特征主要由InSAR观测决定，地震矩释放过程则与P波模型相似，静态与高频GPS观测增加了对破裂时空特征的约束强度；各种比对表明，该模型对各基于单一类型反演模型具有很好的兼容性，棋盘测试展现其具有更优空间分辨率，最小可恢复20 km×20 km尺度的空间特征，压缩了非同震信号或误差导致的零散瑕疵，主、余震破裂具有更好的空间对应关系.主震展布范围为140 km×80 km；4 m以上破裂集中在加德满都以北30 km、深度15 km的狭长区域内，最大滑动量为7.4 m；破裂持续总时长为60 s，破裂速度为3.3 km·s-1，子断层上升时间在10 s内.MW7.3余震破裂区域位于主震东侧边缘，滑动量围绕震中扩散，扩展范围为30 km×20 km，最大滑动量约为4.4 m，总破裂持续时间为35 s.本次地震中静态和高频的GPS观测亦具备独立约束主震破裂扩展过程的能力.
Abstract:On 25 April 2015, the Gorkha earthquake struck the central Nepal, for which diverse data sets including the surface displacements field derived by both InSAR and static GPS, and especially strong ground motions recorded by high-rate GPS are available to depict its rupture process, providing an unprecedented opportunity to assess their contributions to the inversion of the source parameters of the large megathrust earthquake. We investigate the space-time history of fault slip during the Gorkha earthquake mainshock (MW=7.8) and its largest aftershock (MW=7.3, happened 12 days later) using separate and joint inversions of high-rate GPS, static GPS, InSAR data, teleseismic waveform and strong-motion data to pursue a self-consistent and compatible rupture model.
After obtaining the preferred rupture velocity and subfault rise time by using the tradeoff line between the cross correlation coefficients of observed and synthetic waveforms of HRGPS versus rupture velocity and subfault rise time, we performed separate inversions of the individual datasets. Separately inverted models present different slip patterns due to the intrinsic resolution of different datasets. Finally, two joint inversions of the near-field datasets and all datasets have been carried out. The joint model from near-field datasets improves the resolution of GPS model, but is not better than InSAR model. However, the scattered slip patches due to the non-coseismic deformation or observation errors have been depressed in the joint models. The optimal joint model of all datasets, supplemented by far-field observation, can be regarded as a unified model for preserving the common features of all separate inversions and yielding good combined resolution of slip. The Checkerboard tests also show that the unified model has the best spatial resolution for almost recovering the 20 km×20 km slip patch and is more stable to rupture velocity variance. The slip pattern is mainly constrained by InSAR and the temporal process agrees well with teleseismic P waves model. The preferred unified model reveals the slip zone of mainshock extending about 140 km along strike and about 80 km down dip. The large slip patch (slip > 4 m) of an elongated shape is located 15 km deep and 30 km north of Kathmandu, with a maximum slip of 7.4 m. The slip process lasted 60 s with a rupture velocity of about 3.3 km·s-1, and with the rise time of 10 s for each subfault. The slip of MW7.3 aftershock lies to the east of the boundary of mainshock slip zone within an area about 30 km along strike and about 20 km down dip, features a compact pattern with a maximum slip of 4.4 m and total lasing time of 35 s.
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Key words:
- Gorkha earthquake /
- Joint inversions /
- Spatial-temporal rupture process /
- High-rate GPS
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图 1
`尼泊尔地震构造背景及MW7.8主震与MW7.3余震静、动态形变场
Figure 1.
Tectonic setting of the Gorkha earthquake and surface deformation including permanent offsets and kinematic waves caused by MW7.8 mainshock and MW7.3 aftershock
图 2
MW7.8主震与MW7.3余震滑动分布的独立模型
Figure 2.
Slip distributions of MW7.8 mainshock and MW7.3 aftershock obtained by the separate inversions
图 3
联合反演MW7.8主震与MW7.3余震滑动分布
Figure 3.
Slip distributions of MW7.8 mainshock and MW7.3 aftershock obtained by the joint inversions of (a) near-field datasets, (b) all datasets
图 4
MW7.8主震、MW7.3余震地震矩释放率函数
Figure 4.
Moment rate functions of (a) MW7.8 mainshock and (b) MW7.3 aftershock
图 S1
不同子断层上升时间和破裂速度在KKN4垂直向的模拟值与观测值的比较
Figure S1.
Synthetic vertical displacements featured with different rupture velocities and rise times at station KKN4 from the 24 scenario models compared to the observed data (black trace)
图 S3
同震永久形变的模拟值与观测值的拟合残差
Figure S3.
Residuals between observed and synthetic coseismic permanent displacements
图 S5
远震P波的模拟值与观测值的比较
Figure S5.
Comparison of observed and synthetic waves of teleseismic P wave
图 8
平滑因子与归一化残差的折衷曲线
Figure 8.
Trade-off curves indicating normalized inversion residual versus smooth weight for each dataset
表 2
主震各种模型的模拟值与观测值拟合平均残差与互相关系数
Table 2.
Mean residuals and cross correlation coefficients of separate and joint inversions of mainshock
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