Long-term hydrochemical earthquake precursor studies at the Koyna-Warna reservoir site in western India |
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| Authors: | D V Reddy Devender Kumar N Purnachandra Rao |
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| Institution: | 1.CSIR-National Geophysical Research Institute,Hyderabad,India |
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| Abstract: | Koyna-Warna region of western India is an active seismic zone due to the Reservoir Triggered Seismicity (RTS). Earthquake precursor studies are carried out monitoring hydrochemical and stable isotope signatures in the groundwater from 15 bore wells since January 2005, for more than 12 years (January 2005 to February 2017). Depth of these boreholes ranges from 100 to 250 m. Cyclic or temporal variation in hydrochemistry is observed in few sensitive wells in Koyna region. The Govare well in Koyna is found to be most sensitive and the observed hydrochemical cycle is closely associated with local earthquakes of M > 5. The earthquakes M <5 occurring either in Warna cluster or close to the observation wells, did not generate hydrochemical precursory changes. The increase in hydrochemistry is hypothesized as mixing of two aquifer waters with different hydrochemistry. It is noted that a precursory hydrochemical cycle is observed during first quarter of 2015, but no earthquake M > 5.0 occurred till date. The cyclic changes in hydrochemistry, however, indicate on-going earthquake processes and an impending earthquake of M > 5 in the region. |
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