Assessment of maximum earthquake potential of the Kopili fault zone in northeast India and strong ground motion simulation

Abstract

Maximum magnitude (MM) earthquake in the Kopili fault zone of North-East India has been assessed using different approaches, which are primarily dependent on various parameters such as fault geometry, slip rate, geodetic moment rate, and convergence rate. The analyses reveal that the source zone has accumulated strain energy, during the last 72years since 1943, enough to produce a strong earthquake of magnitude≥7. On supplementing with the historical data, we conclude Mw7.3 as the maximum potential earthquake for the Kopili source zone. Such large earthquake, on its occurrence, may cause widespread significant ground shakings and damage to infrastructures in the study region. We, therefore, also simulated strong ground motion, in the form of peak ground acceleration (PGA), for the Mw7.3 potential earthquake using Empirical Green’s Function (EGF) approach for ten different sites. In the analysis, an earthquake of magnitude Mw6.5, which has been simulated using a recorded Mw5.3 earthquake, is used as Green’s Function. The two-step approach is adopted in the simulation process, as the required criteria, i.e., moment ratio of<1000 between the target potential event (Mw7.3) and the element event (Mw5.3) could not be met. We found that the cities like Tezpur, Masamari, Tumuki, Dhekiajuli, Nagaon, Bomdila, Udalguri, Seppa, Hajoi, Behali, Guwahati, and Itanagar that are located∼60–130km from the source zone may experience very strong to moderate ground shaking with PGA ranging between 0.36–0.14g. However, the cities located in the distance range of∼130 – 300km from the source, namely Jorhat, Ziro, Mokokchung, Dhubri, and Kokrajhar are expected to have low ground shaking with PGA<0.14g. The study therefore provides valuable insights to the likely seismic hazard scenario in north-east India.