PROBABILISTIC SEISMIC HAZARD ASSESSMENT OF VPHEP, PIPALKOTI IN CHAMOLI DISTRICT OF UTTARAKHAND

Abstract

Chamoli district of Uttarakhand state in India lies in Seismic zone V as per the hazard zonation map of India; and has a huge potential for river valley projects. There are some operational Hydro Electric Projects (HEPs), many under construction projects and various others are at different stages of inception in this seismically active region. Thus, it becomes necessary to predict the nature of ground shaking in these hydraulic structures to an earthquake stimulus. To study this behaviour, Vishnugad Pipalkoti Hydro Electric Project (VPHEP), Pipalkoti (Chamoli) having coordinates 30°31’08’’N latitude and 79°29’37’’E longitude is selected for performing the PSHA (Probabilistic Seismic Hazard Assessment) and estimating the Peak Ground Acceleration (PGA) with a probability of exceedance of 10% in fifty years. The study area has been selected between the coordinates of longitude 76°E to 82°E and latitude 27°N to 33°N (i.e., 6°latx6°long) with a dam location of VPHEP at the centre. The unified moment magnitude catalogue obtained from various reputed agencies such as USGS, ISC, and NCS has been used in this study. The magnitude of completeness is estimated using Stepp’s method (1972). The study area has been divided into four seismic source zones(SSZ) based on the seismicity and tectonic features of the region. Seismic hazard assessment has been carried out using Boore et al (2003) attenuation relationship in CRISIS2007 software. Peak ground Acceleration ( PGA) of 0.15g, 0.24g, 0.38g, and 0.78g for a probability of exceedance of 50%, 20%, 10%, and 2% in 50 years is obtained in this study. The results thus obtained could be utilized for further risk assessment and disastermitigation studies in the region.