Detailed geophysical and geological investigations to identify copper lead and zinc mineralization around Ambaji, Banaskantha district are in progress.
Quantitative seismic zonation of Gujarat through deterministic seismic hazard assessment (DSHA)
The seismic zonation map assists one in identifying the lowest, moderate as well as highest hazardous zone in terms of earthquake vulnerability and provides a suitable foundation for constructing various structures to resist the effects of earthquake forces. The strong ground motions determined using DSHA methodology provides the quantitative basis for seismic zonation. DSHA methodology has been used by Chopra et al. (2012, 2013) to estimate strong ground motions in the Gujarat region in terms of Peak ground acceleration (PGA) and Spectral acceleration (SA) using the robust modified stochastic finite fault modelling approach based on dynamic corner frequency approach. Based on the past and current seismicity supplemented by active fault studies mainly in Kachchh region, a total of 19 earthquake-generating faults, 12 in Kachchh, 5 in Saurashtra and 2 in Mainland, have been considered for the analysis. The maximum magnitude has been assigned to each fault based on the regional tectonic environment and past seismicity.
The ground motions from these identified sources have been estimated at the surface at numerous points distributed all over the Gujarat region on a grid incorporating the path and site effects obtained using the local earthquake data. The PGA values have been extracted from the generated accelerograms and contoured. The Kachchh region can expect maximum surface accelerations between 400 and 800 cm/s2, Saurashtra and Narmada belts between 100 and 200 cm/s2 and Mainland less than 50 cm/s2 from future large earthquakes. Based on response spectrum studies, single and double story buildings in the Kachchh region can expect spectral accelerations between 800 and 2000 cm/s2 in the natural frequency range of these structures. The buildings of 3–4 stories and tall structures that exist mostly in the cities of Saurashtra and mainland can expect accelerations in excess of 100 cm/s2 during a large earthquake in the Kachchh region.
PGA distribution in cm/s2 in Gujarat region
Chopra S., Kumar D., Rastogi B.K., Choudhury P. and Yadav R.B.S. (2012). Deterministic seismic scenario for Gujarat region, India, Natural Hazards, 60, 517-540.
Chopra S., Kumar D., Rastogi B.K., Choudhury P. and Yadav R.B.S. (2013). Estimation of seismic hazard in Gujarat region, India, Natural Hazards, 65, 1157-1178.