CRUSTAL STRUCTURE OF THE 2015 GORKHA EARTHQUAKE REGION, CENTRAL NEPAL USING GRAVITY DATA

The April 25, 2015 Gorkha earthquake (magnitude 7.5) was centered in central Nepal and caused considerable damage throughout the region including the capital Katmandu. The main event occurred within the Main Himalayan Thrust (MHT) system which is the main fault system accommodating the convergence between India and Asia. Recent geological investigations indicate that the MHT system is complex consisting of several flats and ramps where earthquakes can occur. Despite the abundance of fault systems in the region, the MHT system has been seismically and geodetically inactive since the last large earthquake (1934) that involved the system. Since it has been locked for such a long time, the geometry of the fault system at depth has been difficult to determine using earthquake data. In order to help investigate the geometry of the fault system, a detailed analysis of the available land and satellite gravity will be investigated. These data will be used to create a series of gravity anomaly maps including complete Bouguer, isostatic residual, wavelength filtered and derivative anomaly maps. Estimates of the depth to the fault systems will be estimated using three-dimensional Euler deconvolution, two-dimensional forward modeling and three-dimensional inversion of residual gravity anomaly data. The results of the above analysis will be used to estimate the geometry of the MHT to help determine the location of fault system including regions which are currently seismic locked.