Geodetic plate coupling and seismic potential on the main Himalayan thrust in Nepal

Abstract

We model interseismic plate coupling distribution on the Main Himalayan Thrust (MHT) in Nepal through the inversion of secular GNSS velocity data. To complement previously published data, we compile velocity data from ten additional continuous stations to improve spatial resolution in central and mid-western Nepal. A regional non-planar structural model is adopted to reproduce the MHT fault plane. In general, the coupling pattern seems nearly binary, indicating that transition from full coupling to decoupling is occurring sharply in very narrow zones. In eastern Nepal (> 84.5ºE), plate coupling is very strong from the surface to intermediate depths, including the source region of the 2015 Mw 7.8 Gorkha earthquake. Geodetically estimated slip deficit rates are consistent with the rupture history of great earthquakes in the east revealed by geomorphological observations. In the west (< 83.0ºE), a weakly coupled zone extends laterally at intermediate depths, whereas the coupling in the shallower part remains very strong. Although the slip deficit rate in the west is significantly smaller than that in the east, seismic moment accumulated, since the last complete rupture in 1505 may be capable of generating a future great event. In central Nepal, estimated slip deficit rates are comparable with those in the east, and no great event has been documented over the past several centuries. Thus, the seismic risk may be most urgent in central Nepal. The development of local seismicity and crustal deformation should be carefully monitored.Graphical