A unified source model of the 2015 Gorkha earthquake

作者:Liu Gang; Yang Shao-Min; Shi Hong-Bo; Nie Zhao-sheng; Xiong Wei; Wang Di-Jin; Li Heng; Zhou Yu; Qiao Xue-Jun; Tan Kai; Wang Qi*
来源:Acta Geophysica Sinica, 2017, 60(7): 2663-2679.
DOI:10.6038/cjg20170714

摘要

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 (M-W =7. 8) and its largest aftershock (M-W= 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 X 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 M(W)7. 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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