Tectonic setting and general features of coseismic rupture of the 25 April, 2015 <italic>M</italic><sub>w</sub> 7.8 Gorkha, Nepal earthquake

Abstract

An earthquake of M w 7.8 occurred on 25 April, 2015 in Nepal Himalaya, with a focal mechanism of low-angle thrust, determined unanimously by multiple research agencies. More than 100 aftershocks occurred thus far, including strong ones with magnitude larger than M s7.0, triggered normal-mechanism swarms hundreds of kilometers northeast of the epicenter in Tibet. The mainshock, located in central Himalayan orogenic belt and within the seismic gap between the ruptured zones of the 1934 Bihar M w~8.1 and 1505 Lo Mustang M w~8.2 earthquakes, is the largest one on the Main Himalaya Thrust since 1950 Assam M w~8.4 earthquake. To help a better understanding of the earthquake, we provide in this paper a review on the tectonic setting and geometry of the Himalayan fault system, large historical earthquakes and their rupture areas, pattern of modern microseismicity, general models of seismic cycle in the Nepal Himalaya, and spatial pattern of surface deformation resulted from interseismic loading and coseismic slip. Combining the overall features of coseismic rupture of the mainshock from teleseismic finite fault solutions, we comment on this earthquake regarding to its relationship with the characteristic (typical topography-building) Himalayan events, the comparison with the 2008 Wenchuan M w 7.9 earthquake of similar magnitude, the general condition for low-angle thrust-type rupture reaching surface, and its implication to regional seismic hazard.