Assessment of seismic hazard incorporating site-specific study for Assam, North-East India

Abstract

Abstract In conjunction with site-specific studies, probabilistic seismic hazard assessment (PSHA) is crucial in formulating site-specific response spectra to provide valuable insights into local seismic hazard variations. A site-specific seismic hazard assessment is presented considering a classical probabilistic approach incorporating ground response analysis for Assam, North-East (NE) India. NE India Region is classified into ten seismic source zones depending on the seismicity and tectonics. An updated homogenized earthquake catalogue for 1897–2022 has been used. The seismicity parameters have been calculated with the complete catalogue for each source zone. A topography-based Vs30 model has been considered, and for the application of ground motion prediction equations (GMPEs), a logic tree approach using the log-likelihood method (LLH) has been considered. The hazard maps for Assam are prepared at the bedrock level in terms of peak ground acceleration (PGA) and spectral acceleration (Sa) values. The PGA values vary between 0.23–0.34 g and 0.33–0.51 g for 475 and 2475 years of return period, respectively. The hazard curves and uniform hazard spectra (UHS) have also been presented for ten headquarters of Assam, along with disaggregation studies for Guwahati. Further, borehole data from Guwahati have been considered for evaluating ground responses with the assignment of proper soil conditions. The surface level PGA for Guwahati gets amplified significantly up to 0.41 g and 0.56 g for 475 and 2475 years of return period, respectively. Finally, the surface-level responses have been presented for Guwahati city, one of the ten headquarters of Assam, considering the controlling earthquake.