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Induced seepage along a coastal parallel system of faults as a possible cause of the Koyna earthquakes

NATIONAL GEOPHYSICAL RESEARCH INSTITUTE, HYDERABAD, India

Abstract

The level of seismicity in the area around Koynanagar (17°23'N:73°45'E), Maharashtra State, Western India, has increased considerably since the commissioning of a hydroelectric project on the Koyna river in the year 1962. Analysis of available geological, geochemical, geothermal, refraction seismic, observational seismic, gravitational and paleomagnetic data for the region suggests the existence of a zone of faults, located immediately to the west of the watershed (Sahyadri ridges) and running roughly parallel to the western coast of India, approximately between latitude 17°N to 19°30'N. Geomorphological evidence for recent reactivation of this fault system of Miocene age is presented.

The increase in the seismicity of the region is considered to be due to release of strain accumulated in the zone of faults. It is proposed that induced seepage in the N-S trending faults, of a fraction of the enormous quantities of water discharged in the E-W running Vaitarani-Vashishthi ricers, at the Pophli powerhouse, has actuated and sustained the process of release of seismic energy. Assuming that induced seepage of water is the immediate cause of the earthquakes, a method for mitigation of the seismicity level in the Koynanagar region is suggested.

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