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Earthquakes continue to occur in the vicinity of Shivaji Sagar Lake since its creation by the Koyna Dam in 1962. The seismicity peaked in 1967 with a M 6.3 earthquake which claimed over 200 human lives and destroyed the Koyna township. Earthquakes of M`4 occur every year following an increase of water level in the reservoir. During 1973During , 1980During and 1993 earthquakes exceeding magnitude 5 occurred. Most earthquakes of M`4 are associated with pronounced foreshocks and aftershocks. Starting Sepember 1993, seismic monitoring was vastly improved with the deployment of additional close-by stations (analog and digital). The focal parameters now available have enabled delineation of the active faults and deciphering of the earthquake nucleation process. During 1995 -96, 13 boreholes were drilled to depths of 130 to 250 m and measurement of water levels in these wells was initiated. A preliminary analysis of one year's data from a borehole 1 km south of Koyna reveals tidal signatures, indicating connection of the well to a confined aquifer which is favorable for detection of pore pressure anomalies induced by crustal strain. We hope to improve our understanding of the genesis of reservoir-induced earthquakes at Koyna with these new measurements.

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The Koyna Dam site in western India has been seismically active since its impounding in 1962. The seismicity peaked in 1967 when an earthquake of magnitude 6.3 claimed 200 human lives and caused some damage to the dam itself. Subsequently, bursts of seismicity with M ≧ 5 earthquakes have occurred during 1973, 1980, and 1993 to 1995. The epicenters during the latest burst are concentrated around the newly impounded Warna reservoir, 25 km south of Koyna. Several shocks of smaller magnitude have occurred in this area since 1967 under the influence of the Koyna (Shivajisagar) reservoir, but the impoundment of the Warna reservoir to over 60 m has led to the enhanced seismic activity in the region. The space-time pattern of epicenters located for the period 28 August 1993 to 31 December 1995 clearly delineates two parallel trends in the NNE-SSW direction. The correlation between seismic activity and water levels in both the reservoirs suggests that the present activity was influenced more by the Warna than the Koyna reservoir. The discriminatory characteristics of reservoir-induced seismicity based on b-value, foreshock-aftershock pattern, and decay rate of aftershocks continue to be valid.

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