A multi-scenario based micro seismic hazard assessment of the Bhuj City, western India incorporating geophysical and geotechnical parameters

Abstract

The micro-seismic hazard assessment (micro-SHA) of the Bhuj city (highest seismic zone V) has been accomplished considering seismotectonic as well as shallow subsurface modeling through geophysical (multi-channel analysis of surface waves (MASW) survey at 19 sites) and geotechnical parameters from 28 boreholes distributed in the entire Bhuj city. The average shear wave velocity through the MASW survey at 30 m depth (VS30) is estimated in the range of 400–915 m/s (NEHRP C-type and B-type soil classes). Seismotectonically justified a total of 54 scenario-earthquakes (SEQs) along all major faults have been considered to evaluate the strong ground motion at generic soil level having a shear wave velocity of 760 m/s and depth of 12–28 m. The surface level strong motion (SM) has been estimated through ground response analysis preparing soil models along all boreholes. The PGA at the surface in Bhuj city has been estimated in the range of 528 cm/s2 to 1020 cm/s2; highest in the central-western part of the Bhuj city where clay with high plasticity is present. The mean-spectral acceleration over the study area for 0.2 s (corresponding to 1-2 story), 0.55 s (4-5 story), 1sec (high rise) and 1.25 s period (large structures) are prepared at the surface from all scenario earthquakes. The amplification of SM in the Bhuj city is computed in the range of 1.7–3.7.

Keywords

• Multiple seismic scenarios
• Shallow subsurface modeling
• Ground response analysis
• Seismic hazard assessment