Simulation of Strong Ground Motion for an Mw 7.0 Earthquake beneath the Bhutan Himalaya in NE India and its trans-boundary seismic hazard implications

Abstract

We simulate the strong ground motion for an expected major earthquake (Mw 7.0) beneath the Bhutan Himalayan region with an empirical Green's function method using waveforms recorded from the 2009 Bhutan mainshock (Mw 6.1) and its largest aftershock (Mw 5.1). Fault orientation and location of the simulated event extend the length of the fault plane determined from the 2009 Bhutan mainshock and aftershock along its strike. The simulated PGA values are compared with the results derived from a ground motion prediction equation (GMPE) for the Himalayan region and it is found that different levels of accelerations are associated with different rupture initiation points on the fault plane. It is observed that the NE Indian region is capable of generating peak ground acceleration (PGA) in exceedance to 121 cm/s2 for simulated earthquake (Mw 7.0). The maximum impacts of shaking will be on the sites located near the rupture initiation points that are poised to generate higher values of ground acceleration. To validate our simulation, we also estimate the extent of rupture directivity of the simulated earthquake with respect to four initiation points indicating that higher value of PGA and shaking duration exist either to South or to South-West azimuths from the imitated locations, which are corroborated with respective geology of the sites. This study suggests that areas of maximum ground shaking would occur in the vicinity of the source initiation where possibility of relatively stronger earthquake hazards does exist, which in turn requires attention for adoption of earthquake risk mitigation plans in view of impacts of trans-boundary earthquakes in the region.