Search for hydraulic connectivity between surface reservoirs and surrounding aquifers in the reservoir-triggered seismic environment (Koyna region, India) using hydrochemical and isotopic signatures

Abstract

Triggered seismicity is an accepted hypothesis in the present days. However, detailed hydrogeological investigations are lacking in the well-known reservoirtriggered seismic (RTS) zones. Here, we made an attempt to understand the direct linkage between the well-known Koyna-Warna reservoirs believed to be under the RTS zone (situated in the Deccan volcanic province (DVP), India) and the surrounding groundwater system up to 250 m deep from the ground surface. Seismic activity in the region started soon after the impoundment of water in the Koyna reservoir and being continued over the last four and a half decades. Though researchers have carried out numerous studies on the Koyna seismicity, no hydrogeological investigations were attempted. Hence, hydrogeological, hydrochemical, and isotopic investigations were carried out for 7 years on groundwaters from 15 deep bore wells (up to 250 m) and two surface reservoir waters to elucidate the direct hydraulic connectivity between them. No appreciable seasonal change was observed in piezometric heads of the artesian wells, but the semi-artesian wells did show fluctuation of~2 to 12 m during different years, which did not have any relation with the reservoir water levels. No considerable seasonal change in hydrochemistry was observed in individual wells due to the confined nature of the aquifers. The hydrochemical and δ 18 O data of the studied deep groundwaters and reservoir waters, being different from each other, rule out the possibility of direct hydraulic connectivity between them and surrounding groundwater (up to 250 m), even though favorable topographic conditions exist for linkage. The radiocarbon ages, being incomparable between different well waters, support the inference drawn from hydrochemistry and stable isotope data.

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Geospatial techniques for deciphering groundwater potential zones of reservoir-induced seismicity region in western India using analytical hierarchy process

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