Probabilistic seismic hazard mapping of National Capital Region of India using a modified gridded seismicity model

Abstract

This is the first comprehensive study for a seismic macro-zonation of the National Capital Region of India by using the probabilistic seismic hazard analysis approach. A modified gridded seismicity model is used for this purpose, in which the earthquake occurrence rates obtained using the Gutenberg-Richter's (G-R) relationships for conventional area type seismic sources are distributed non-uniformly among a grid of cells. This provides a more robust approach than the commonly used weighted sum of area sources of homogeneous seismicity and the zone-free smoothed gridded seismicity. Other distinguishing features of the present analysis include: detailed seismotectonic evaluation of the region to identify seven area type seismic sources, compilation of a comprehensive earthquake catalogue for the estimation of seismicity recurrence parameters, selection of the most appropriate ground motion prediction equation by using a database of 71 strong motion accelerograms recorded in the region, and estimation of the compatible distance parameters by associating a fictitious fault rupture plane to each grid cell with appropriate strike and dip angles. Hazards maps are prepared for the hard rock site condition in terms of the peak ground acceleration and the 5%-damping acceleration response spectrum amplitudes for several combinations of natural periods and return periods. A simple empirical approach is also developed to obtain amplification factors for modifying the uniform hazard response spectra for the rock sites to those for the soil sites with a given VS30 value. The hazard estimates from this study are found to be somewhat higher with greater site-to-site variations as compared to those from the earlier studies.