Constraints on Source Parameters of the 25 April 2015, M w = 7.8 Gorkha, Nepal Earthquake from Synthetic Aperture Radar Interferometry

We present InSAR observations of the co-seismic deformation caused by the Mw 7.8 Gorkha, Nepal earthquake. Analysis of Sentinel-1 data revealed about 100 x 100 sq. km surface deformation with ~1 m upliftment near Kathmandu, and ~0.8 m subsidence towards north along the line of sight of the satellite. The maximum deformation is observed about 40 km east-southeast of the epicentre, suggesting eastward propagation of the rupture. Elastic dislocation modelling revealed that the overall rupture occurred on a 170 km long, 60 km wide fault along the strike (286°) and dipping north (dip = 15°) with large amount of slip (4.5 m) confined to the centre (95 x 22 sq. km) and less slip (0.25 m) on the surrounding part of the fault plane. The corresponding moment magnitude is M_w 7.75. The area, depth and dip of the modelled fault plane are fairly consistent and overlap with the location of mid-crustal ramp in the Main Himalayan Thrust. We infer that the earthquake was possibly caused by the release of inter-seismic strain energy accumulated in the environs of mid-crustal ramp due to plate boundary forces.