Seismic zoning maps of the National Capital Region (NCR) of India

Abstract We present seismic zoning maps of the National Capital Region (NCR) of India in terms of uniform hazard spectrum (UHS) amplitudes using three different attenuation equations to model the contributions of local earthquakes around the region and distant earthquakes in northwestern Himalaya (NWH) and Hindu Kush Subduction (HKS) sources. Our results show that the shape of design spectra must depend on the nature of contributing earthquake sources, their relative activity, the potential to create large magnitudes, and their geographical placement relative to the site selected for hazard computation. Our results also show that specifying strong motion amplitudes for use in engineering design by means of peak ground acceleration and a standard spectral shape may result in significant underestimation of intermediate and long‐period ground motions critical for buildings higher than four to five stories and hence should not be used. We present zoning maps for nine possible combinations of three different local geological site conditions (sediments, intermediate sites, and basement rock sites) and three different soil site conditions (“rock,” stiff soil sites, and deep soil sites). One of these maps can be readily used to extract the UHS amplitudes of the pseudo relative velocity spectrum (PSV) at any site in the NCR by specifying the local geological site‐condition parameters from a high‐resolution surface geological map of the region and determining the local soil site conditions by experiments limited to the site alone. The paper also provides a geological map of NCR on a scale of 1:1 million for a rough idea of the local geological parameters for a site of interest.