Ground motion modelling in the Gujarat region of Western India using empirical Green's function approach

Abstract

In this study, ground motions are estimated for scenario earthquakes of Mw 6.0, 6.5 and 7.0 at 17 sites in Gujarat region using Empirical Green's function technique. The Dholavira earthquake of June 19, 2012 (Mw 5.1) which occurred in the Kachchh region of Gujarat is considered as an element earthquake. We estimated the focal mechanism and source parameters of the element earthquake using standard methodologies. The moment tensor inversion technique is used to determine the fault plane solution (strike=8°, dip=51°, and rake=−7°). The seismic moment and the stress drop are 5.6×1016Nm and 120bars respectively. The validity of the approach was tested for a smaller earthquake. A few possible directivity scenarios were also tested to find out the effect of directivity on the level of ground motions. Our study reveals that source complexities and site effects play a very important role in deciding the level of ground motions at a site which are difficult to model by GMPEs. Our results shed new light on the expected accelerations in the region and suggest that the Kachchh region can expect maximum acceleration of around 500cm/s2 at few sites near source and around 200cm/s2 at most of the sites located within 50km from the epicentre for a Mw 7.0 earthquake. The estimated ground accelerations can be used by the administrators and planners for providing a guiding framework to undertake mitigation investments and activities in the region.