Audit of stored strain energy and extent of future earthquake rupture in central Himalaya

Abstract

The deadly 25 April 2015 Gorkha earthquake (Mw=7.8) and aftershocks have partially released the accumulated interseismic strain along the Main Himalayan Thrust (MHT). Postseismic deformation associated with this earthquake is mainly confned to the north of the rupture. This suggests possible occurrence of future large events towards west or south, where MHT is locked. Asperities arising due to heterogeneity in the stress-strain patterns are believed to play a major role in controlling the coseismic rupture propagation. We determine interseismic coupling along the MHT and spatial variations in total strain rate using two decades of GPS, InSAR and sprit leveling data. Further, b-values derived from the seismicity data are used to identify zones of stress accumulation. We demonstrate that the 2015 earthquake ruptured an asperity which hosted high strain and stress accumulation prior to the event. A similar asperity towards west of the epicenter with unreleased strain energy is identifed. This could spawn a future large earthquake akin in magnitude to the 2015 Gorkha event. These fndings compel a revisit of the seismic hazard assessment of the central Himalaya.