Stochastic ground-motion simulation of two Himalayan earthquakes: seismic hazard assessment perspective

Abstract

The earthquakes in Uttarkashi (October 20, 1991, M w 6.8) and Chamoli (March 8, 1999, M w 6.4) are among the recent well-documented earthquakes that occurred in the Garhwal region of India and that caused extensive damage as well as loss of life. Using strong-motion data of these two earthquakes, we estimate their source, path, and site parameters. The quality factor (Q β ) as a function of frequency is derived as Q β (f)=140f 1.018 . The site amplification functions are evaluated using the horizontal-to-vertical spectral ratio technique. The ground motions of the Uttarkashi and Chamoli earthquakes are simulated using the stochastic method of Boore (Bull Seismol Soc Am 73: 1983). The estimated source, path, and site parameters are used as input for the simulation. The simulated time histories are generated for a few stations and compared with the observed data. The simulated response spectra at 5% damping are in fair agreement with the observed response spectra for most of the stations over a wide range of frequencies. Residual trends closely match the observed and simulated response spectra. The synthetic data are in rough agreement with the ground-motion attenuation equation available for the Himalayas (Sharma, Bull Seismol

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

“…Ameer et al (2005) performed a PSHA for Iraq using a complete earthquake catalogue. To date, many studies are available on seismic hazard assessment for the whole of India or different parts at a regional level using both deterministic and probabilistic approaches (Sharma 2003;Sharma and Lindholm 2012;Nath and Thingbaijam 2012;Mojarab et al 2023;Harbindu et al 2012;Mahajan et al 2010;Shanker andSharma 1998, Raghukanth 2010). Furthermore, a global seismic hazard map has been developed by the Global Earthquake Model (GEM) foundation that is updated in 2023 with a 10% PoE in 50 years for reference rock conditions and shear wave velocity, Vs30 of 760-800 m/sec (Jhonson et al 2023).…”