Seismic Site Response Studies for the Indo-Gangetic Plains of India with Special Emphasis on the Narora Nuclear Power Plant

The Indo-Gangetic Plains (IGP), India, is one of the most seismically vulnerable regions due to its proximity to the Himalayan earthquakes. In this study, an attempt has been made to estimate seismic site response analysis around the Narora Nuclear Power Plant (NNPP) located in the central part of the IGP. A non-linear approach has been used for site response analysis with simulated accelerograms as input motion at three different competent bedrock types: weathered rock, unweathered rock, and hard rock at depths of 30 m, 80 m, and 175 m, respectively. The 1999 Chamoli earthquake of magnitude ( M w ) 6.6 is used as a possible source in the Himalayan region that may affect the NNPP site in the future. The results show that at the NNPP site amplification ( F PGA , F PSA ) and site factors ( F A and F V ) vary in the range of 2.19–4.77, 2.20–5.12, 2.42–4.36, and 1.34–2.5, respectively, for 30 m to 175 m depth. The relative percentage changes in the amplification and site factors at the surface have been studied when the input motion bedrock depth changes from 30 to 175 m. We observed maximum amplification at NNPP sites for a frequency range of 2–5 Hz. The site predominant frequency maps have been prepared for the study region and these frequencies are in the same range of fundamental frequency of existing civil structures. There is a slow amplification of PGA values from 175 to 30 m but there is a sharp increase in the PGA values for shallow depth less than 30 m. The estimated seismic site response in the IGP will be helpful to assess damage for existing and upcoming structures due to future earthquakes from the Himalayan central seismic gap.