CRUSTAL STRUCTURE OF CENTRAL NEPAL USING GRAVITY DATA

The crustal structure of central Nepal is currently known from widely spacing broadband seismic studies and magnetotelluric data. Determining the crustal structure is important in construction of the tectonic history of the Himalayan orogeny. Additionally, a major earthquake occurred on April 25, 2015 Gorkha earthquake (magnitude 7.5) that 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. Geological investigations indicate that the structure of 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). 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 and the general crustal structure of central Nepal, a detailed analysis of the available land, airborne 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.