Drained and undrained responses for Koyna-Warna earthquakes from 1993 to 1994 following impoundment of the Warna reservoir in India

摘要

The Koyna region along the west coast of India in Maharashtra, is a unique case of reservoir triggered seismicity, where seismicity has been reported since 1963 after the initial impoundment of the Shivajisagar reservoir behind Koyna dam in 1961. The region was further destabilized following the filling of the Warna reservoir, situated 25 km south of Koyna, during the late 1980s. Increase in pore pressure by drained and undrained effects is known to weaken the substratum below a water reservoir, facilitating the onset of seismicity. Although their relative influences may vary with time and space, it is difficult to separate their individual contributions. The present study, using the well-located earthquakes of M >= 5 for the period 1993-94, is a preliminary attempt to identify these effects after impoundment of the Warna reservoir. It could provide a good opportunity for further modelling the strength changes due to reservoir impoundment.