Seismic hazard assessment of the Shillong Plateau, India

Abstract

The Shillong Plateau is an earthquake-prone region in the northeastern India. Based on regional seismotectonic studies, we present here a deterministic seismic hazard assessment (DSHA) and maps of peak horizontal accelerations (PHA) for three largely populated districts – the East Khasi hills, the Ri-Bhoi, and the West Garo hills – within the Shillong Plateau. The hazard analysis methodology is based on the analysis of 72 earthquake sources (active faults) located within 500 km seismotectonic region around the plateau. Using an average sample log-likelihood approach, suitable ground motion prediction equations (GMPEs) are identified. As a variation in hypocentral distances can affect the ranks (or weights) of selected GMPEs, DSHA is performed separately for the three selected districts. Analyses show that the northern part of the East Khasi hills, eastern part of Ri-Bhoi district and the West Garo hills districts exhibit the highest PHA value of 0.46 g at site class A (hard rocks). In addition, response spectra for the Shillong city, Nongpoh, and Tura indicate that the maximum spectral acceleration reaches 0.67 g, 0.77 g, and 0.64 g at 0.1 s, respectively. These assessments indicate that the Barapani, Oldham, and Dauki faults influence significantly the seismic hazard in the studied region.