Seismic Hazard Estimation for Southwest India

The objective of the study is to understand the seismicity of the Western coast and its adjoining regions whose seismic potential has not been evaluated so far. The study area encompasses a major portion of Karnataka and Northern part of Kerala and Goa. The approach incorporated in the study is probabilistic in nature and attempts to capture the uncertainty involved in various phases of hazard estimation. The seismic sources in the study region are mostly diffused in nature and are modeled as areal sources with uniform seismicity within a source zone. Regionally, adaptable ground motion prediction equation constitutes the ground motion modeling. The epistemic uncertainty involved in the selection of ground motion models is addressed by adopting a logic tree approach. The seismic source model and the ground motion model are combined together to produce hazard curves for the study region. Most of the ground motion prediction equations are developed for hard rock conditions (Vs > 800 ms−1). However, most of the built environment rests on the soil and there is a necessity to estimate the hazard values at the surface level. Based on the site topography, it was observed that majority of the study area belongs to NEHRP site class C and D. The hazard values were estimated for the boundary site condition CD (310 < VS (30) < 520 ms−1) using a nonlinear site amplification model. Seismic hazard maps produced from this study are believed to be of immense use for building planners and designers.