Estimation of Seismic Site Coefficient and Seismic Microzonation of Imphal City, India, Using the Probabilistic Approach

Seismic site coefficients (Fs) for Imphal city have been estimated based on 700 synthetically generated earthquake time histories through stochastic finite fault method, considering various combinations of magnitudes and fault distances that may affect Imphal city. Seismic hazard curves and Uniform Hazard Response Spectra (UHRS) are presented for Imphal city. Fs have been estimated based on site response analyses through SHAKE-91 for a period range of engineering interest (PGA to 3.0 s), for 5% damping. Fs were multiplied by UHRS values to obtain surface level spectral acceleration with 2 and 10% probability of exceedance in 50 year (∼2500 and ∼500 year) return period. Comparison between predicted mean surface level response spectra and IS-1893 code shows that spectral acceleration value is higher for longer periods (i.e., > 1.0 s), for ∼500 year return period, and lower for periods shorter than 0.2 s for ∼2500 year return period.