Probabilistic seismic hazard assessment for some parts of the Indo-Gangetic plains, India

Abstract

Indo-Gangetic plains are seismically most vulnerable due to the proximity of adjacent great Himalayan earthquakes and thick alluvium deposits of the Ganga River system. As the urbanization on this plain is increasing, there is a need to quantify seismic hazard in the Indo-Gangetic plains (IGPs). IGP also includes major cities with high population density. A probabilistic seismic hazard analysis (PSHA) plays an essential role in ensuring the safety of buildings, bridges and nuclear power stations. A seismic hazard analysis (SHA) was performed deterministically for most of the atomic power stations in India. An attempt has been made to perform PSHA of the part of Indo-Gangetic plains around Narora nuclear power plant (NNPP), accounting for a wide variety of uncertainties associated with SHA. Geological and tectonic features, as well as seismicity distribution around NNPP, are studied in detail, and four source zones are identified according to the geology, seismotectonics and diffuse seismicity. Mmax values for all the source zones based on 300-km distance around NNPP are 7.61 ± 0.54 for Himalaya zone (Zone 1), 6.12 ± 0.54 for Indo-Gangetic Peninsular India (IGPI) East zone (Zone 2), 6.29 ± 0.54 for IGPI Central zone (Zone 3) and 6.38 ± 0.64 for IGPI West zone (Zone 4). The b-value and return period of earthquakes in these zones are also estimated using Kijko–Sellevoll–Bayes model. The hazard curve for peak ground acceleration (PGA) and pseudo-spectral acceleration (PSA) at 0.2 s for the study region is obtained. Hazard map shows a PGA value of 0.0294 g for 100-year return period, 0.0616 g for 475-year return period design-based earthquakes, 0.1033 g for 2475-year return period maximum considered earthquakes, 0.1508 g for 10K-year return period and 0.2598 g for 100K-year return period level at PGA considering all source zones. Similarly, the hazard curve and maps for PSA at 0.2 s are also plotted. According to seismic zonation map of India, most of the study area lies in Zone 4, and the PGA values reported in seismic zonation map and Global Seismic Hazard Analysis Program for the study area range from 0.3 to 0.4 g. The obtained PGA values denote the maximum expected PGA at bedrock level in the study area.