Coseismic and early postseismic deformation due to the 25 April 2015, Mw 7.8 Gorkha, Nepal, earthquake from InSAR and GPS measurements

Abstract

Analysis of Interferometric Synthetic Aperture Radar (InSAR) and Global Positioning System (GPS) data reveals coseismic and early postseismic (4–88 days) surface displacements associated with the 25 April 2015, Mw 7.8 Gorkha, Nepal, earthquake. The pattern of early postseismic surface uplift and subsidence is found to be opposite to that of the coseismic motion. InSAR and GPS data were jointly inverted for coseismic and postseismic slip on the Main Himalayan Thrust (MHT). We consider a complex ramp-flat-ramp-flat subsurface structure of theMHTwith four connected fault planes dipping toward north fromthe Main Frontal Thrust (MFT). The inverted coseismic slip distribution follows an elliptical pattern, extending east-southeastward from the hypocenter with maximum amplitude of 5.7m above the upper edge of the midcrustal ramp. We infer early postseismic afterslip (4–16 days) of 0.2–0.47mtoward downdip of the coseismic slip asperity and another patch with 0.1–0.2m slip toward east. The shallow portion of the MHT toward south is found to have remained unruptured during the earthquake, nor did it slip aseismically after the earthquake, suggesting possibility of large events in the future.