Fault slip distribution of the 2015 Mw7.8 Gorkha (Nepal) earthquake estimated from InSAR and GPS measurements

Abstract

Inversion of the coseismic slip distribution is important for understanding seismogenic mechanisms. In this study, the geometric parametersand uncertainties for the 2015 Gorkha earthquake in Nepal were inverted using a Bayesian approach. The coseismic fault slip distribution was inverted based on triangular dislocations from interferometrc synthetic aperture radar (InSAR) and Global Positioning System (GPS) surface displacement measurements. The inversion results show that the rupture propagated southeast for approximately 140 km, with most of the slip constrained within 30 - 40 km along the dip direction. There are two peak slips in the slip distribution: a ∼5.9 m slip located ∼50 km southeast of the epicenter at a depth of 10.2 km, and a ∼6.32 m slip located ∼100 km southeast of the epicenter at a depth of 10 km. Near the Mw7.3 aftershock, the rupture propagated to the north and southeast. The gap in slip formed between the mainshock and the Mw7.3 aftershock is similar to the shape of a “crocodile with an open mouth”. The results of the triangular dislocation model can explain the GPS-based coseismic displacements and the InSAR deformation field when compared with a classic rectangular dislocation, with a 10.6 cm reduction in the average residual of the InSAR data and a 2 cm reduction in the average residual of the GPS deformation. Compared to the geometry of a ramp—flat—ramp structure, we postulate that both a single-segment and multiple-segments are possible near Kathmandu.