Inversion for Coseismic Slip Distribution and Afterslip of the 2015 Nepal Mw 7.9 Earthquake Using Angular Dislocations

The 2015 Nepal Mw 7.9 earthquake occurred in the central segment of the Himalayan collision zone where the rigid Indian plate is underthrusted beneath the Tibetan Plateau. Refining the coseismic slip distribution and afterslip of the earthquake has great significance for better understanding the seismogenic mechanism in Himalaya orogenic belt. We adopted the angular dislocation elements to construct the rampflat-ramp-flat fault geometry of the main Himalayan thrust. In combining with GPS and InSAR data, we inverted the coseismic slip distribution and afterslip of the Nepal earthquake. The result shows that the mainshock is dominated by thrust slip with minor right-lateral strike-slip. The maximum slip of the mainshock is up to 7.8 m at a depth of 15 km, near to the intersection between the upper flat and mid-crust ramp. The total geodetic moment based on our preferred slip model is M₀=8.39×10²⁰ N·m, corresponding to an Mw of 7.93 assuming a shear modulus of 30 GPa. The released moment is mainly confined to the depth of 15-25 km, in which nearly 50% of the released moment locates at the ramp of upper crust. The maximum slip could be underestimated if we ignore the mid-crust ramp. The inferred afterslip primarily concentrates on the downdip of the coseismic rupture. The afterslip is characterized by pure thrust slip with the maximal amplitude of 0.5 m. The total released moment by the afterslip is estimated to be 1.02×10²⁰ N·m, equivalent to an Mw 7.3 earthquake, approximately 12% of the coseismic moment. The coseismic static Coulomb stress change suggests that the southern part to the rupture zone of the Nepal earthquake with a width of about 60 km is largely promoted by the 2015 Nepal earthquake. Considering the fact that this area is strongly locked during the interseismic period, the near-term seismic hazard in this area deserves special attention.