Artificial water reservoir-triggered earthquakes with special emphasis at Koyna.

摘要

Globally, about one hundred sites are known where filling of artificial water reservoirs triggered earthquakes. It is noteworthy that a majority of the sites where triggered earthquakes exceeding magnitude 5 have occurred are in Stable Continental Regions. The triggered seismicity at Koyna, Maharashtra, India is a classical example where such events have continued to occur for over 41 years since impounding of the Shivaji Sagar Lake in 1962. Detailed investigations in the Koyna region have shown that triggering of earthquakes is influenced by rate of loading, the highest water levels reached and the duration of retention of high water levels as well as Kaiser effect. It is also proposed that increase in heterogeneity in the Koyna region and occurrence of 18 earthquakes of magnitude 5 or more may not have left a large enough fault segment for re-occurrence of another M 6.3 earthquake as in 1967. However, we believe that smaller earthquakes will continue to occur here for another 3 to 4 decades making this an ideal site for monitoring earthquake precursors, which may lead to forecast of M ~5 earthquakes. This optimism is based on the fact that earthquakes in the Koyna region are restricted to a small area of 30x20 km and within a focal depth of 12 km, and there are no other seismically active regions in the near vicinity.