Comprehensive surface level seismic hazard assessment for the state of Gujarat, India: implications for resilient infrastructure and communities

Abstract

The present research presents an updated seismic hazard map for the Gujarat region, regarded to be among the most earthquake-prone intraplate regions globally. The region experienced two catastrophic earthquakes with magnitudes over MW 7 (1819 Allah Bund earthquake; Mw 7.8 and 2001 Bhuj earthquake; MW 7.7) in less than the span of 182 years, along with several moderate events that resulted in numerous casualties and major financial losses to the state. The high rate of industrial development and upcoming new mega and smart cities projects demand an updated hazard map of the region to mitigate the seismic hazards. The study area is categorized into seven seismogenic zones based on seismotectonic features and local geology. A probabilistic seismic hazard assessment (PSHA) map was developed using regional and global attenuation equations in accordance with the Classical Cornell methodology. Peak Ground Acceleration (PGA) and Spectral Acceleration (SA) were assessed at the NEHRP soil class B/C boundary and at the surface level, considering probabilities of exceedance of 2% and 10% over 50 years. We utilized the results of the MASW survey conducted in diverse geological formations across Gujarat to define the sites and determine amplification factors for surface-level ground vibrations. The uncertainties in the hazard assessment are minimized through the Logic tree approach. Using the logic tree method at the B/C boundary, the Bhuj region exhibits maximum PGA values of 0.21 g and 0.51 g for exceedance probabilities of 10% (475-year return period) and 2% (2475-year return period) respectively. Rann of Kachchh, shows the maximum PGA is 0.27 g and 0.57 g for the same exceedance probabilities at the surface level. The SA for 2% and 10% P.E were also estimated at 0.2 s and 1.0 s for the entire Gujarat region. This present study will be useful for developing a more robust earthquake resilient society around the study area.