Effect of the Size of Shillong Plateau on Relative Weightage of Selected Attenuation Relations for Seismic Hazard Analysis

The Shillong Plateau (SP) located in northeast India covers an area of 25,000 km(2). Recent study found that seismic hazard of the SP is affected by four different seismic source zones viz. Shillong Plateau-Assam Valley Zone (SP-AVZ), Indo-Burma Ranges Zone (IBRZ), Bengal Basin Zone (BBZ), and Eastern Himalaya Zone (EHZ). The hypocentral distances from the above mentioned source zones to different parts of the SP are significantly varying. Present study found that this variation in hypocentral distance affects the weights of applicable ground prediction equations (GMPEs) for different parts (based on information theoretic approach) and consequently the seismic hazard of the SP. It is found that the GMPE having the highest weight in the western part of the SP has a lower weight in the eastern part and vice versa. These findings suggest seismic hazard analysis of larger areas like the SP should be attempted by dividing into sub-regions rather a single study area.