Geometry-dependent rupture process of the 2015 Gorkha, Nepal, earthquake determined using a dip-varying inversion approach with teleseismic, high-rate GPS, static GPS and InSAR data

Abstract

SUMMARYFault geometry is widely recognized as one of the most important factors that affect the rupture process and damages of earthquakes. However, there have been few earthquake cases in which the close relation between the fault geometry and rupture process is resolved from inversions of seismic and geodetic observations. In this study, we develop an approach to simultaneously estimate the rupture process and dip-angle variation on the fault. The effectiveness of our new approach was validated through inverse numerical tests. We apply the new approach to the 2015 Mw7.8 Gorkha earthquake and obtain a dip-varying rupture model by jointly inverting the teleseismic, near-fault high-rate GPS, static co-seismic GPS and InSAR data. Our results show a ramp–flat décollement-ramp fault geometry of the earthquake. The shallow ramp may have prevented the rupture from breaking through to the surface. The variation of dip angle changing with depth leads to significantly different rupture velocities and rupture lengths at shallow and deep fault portions. Particularly, the northeastern downdip ramp behaves as a geometric barrier and rapidly slows down the rupture propagation in 35–45 s after the rupture initiation. In contrast, the rupture duration and fault length in the updip portion are relatively long since there is no significant lateral dip change. Furthermore, the approach can improve our understanding of the relationship between rupture behaviour and fault geometry for other thrust low-dip-angle (dip < 45°) earthquakes.