Coseismic Slip Model of the M 7.8 2015 Nepal Earthquake and its M 7.2 Aftershock from Joint Inversion of InSAR and GPS Data

Abstract:

We derived a coseismic slip model for the M 7.8 2015 Nepal earthquake on the basis of radar line-of-sight displacements retrieved from RADARSAT, ALOS and SENTINEL interferograms and GPS data. We use the surface trace of the Main Himalayan Thrust (MHT) and moment tensor solution to approximate the earthquake rupture plane with a planar thrust fault having a strike of ~295° and a dip of ~10°. Our rupture model suggests that the slip area is about 120 x 50 km, with the most of the moment release limited to a depth between 10-20 km. Therefore the earthquake did not reach the surface suggesting a marked shallow slip deficit in the slip depth distribution. The earthquake released a seismic moment of 7.88E+20 Nm, corresponding to a Mw 7.88. Adopting the same fault geometry we also estimated the slip distribution related to the M 7.2 aftershock that occurred near the eastern end of the main coseismic asperity. The aftershock rupture model shows a more compact slip area of about 30 x 30 km, releasing a moment of 5.49E+19 Nm and corresponding to a Mw 7.13. We calculated the static stress changes on the assumed fault plane due to the mainshock. The result suggests loading of the fault around the main coseismic patch where indeed most of the aftershocks, comprising the M 7.2 event, were primarily distributed. Future researches will be focused on the up-dip locked portions of the MHT that did not break during the 25 April 2015 Nepal earthquake and the monitoring of the post-seismic phase by means of InSAR and GPS data.