The 2015 April 25 Gorkha (Nepal) earthquake and its aftershocks: implications for lateral heterogeneity on the Main Himalayan Thrust

The Mw 7.8 Gorkha (Nepal) earthquake on 2015 April 25 initiated ∼80 km northwest of the capital city of Katmandu and ruptured ∼150 km of the frictionally locked downdip segment of the Main Himalayan Thrust (MHT) beneath the central Nepal Himalaya (Avouac et al. 2015). The earthquake resulted in ∼4 m of average slip of the Himalayan Mountains over the Indian Plate in the SSW direction (Mitra et al. 2015). The main-shock fault spanned between the meisoseismal zone of the 1505 (Mw > 8.5) earthquake to its west (Kumar et al. 2006) and the rupture zone of the 1934 (Mw 8.2–8.4) Nepal earthquake to its east (Bilham & Wallace 2005; Sapkota et al. 2013). The last known great earthquake in this region of Nepal occurred in 1833 (M ∼7.5) (Ambraseys & Douglas 2004) and has a significant overlap with the rupture area of the Gorkha main-shock (Adhikari et al. 2015). The main-shock was followed by a series of moderate-to-strong aftershocks, the largest one (Mw 7.3) occurred 18 d after the main-shock, on 2015 May 12 (Fig. 1). Albeit the loss of life and property inflicted by this damaging earthquake and its aftershocks, it has provided an unprecedented opportunity to study the source properties of Himalayan mega-thrust earthquake and its relationship to the geometry of the MHT, which, so far, is poorly understood.