Artificial Water Reservoir Triggered Seismicity (RTS)

A variety of anthropogenic activities are now known to have triggered earthquakes. These include mining, filling of artificial water reservoirs, production of petroleum and geothermal energy, high- pressure fluid injections into shallow crust and many more. Among these, artificial water reservoir triggered seismicity (RTS) is most prominent, with the largest triggered earthquake of M 6.3 having occurred at Koyna, India in 1967. Whether, the devastating Mw 7.8 Sichuan, China earthquake of 8 May 2008 that claimed some 80,000 human lives was triggered by filling of the nearby Zipingpu reservoir, continues to be debated.

There are over 100 sites globally where RTS events of M ≥ 4 have occurred. Here we present an over view of RTS, common characteristics of the RTS earthquake sequences that help to discriminate them from normal earthquake sequences and also help selection of safer sites for locating dams to create artificial water reservoirs.

Koyna, near the west coast of India continues to be most prominent site where triggered- earthquakes have been occurring since the impoundment of the reservoir in 1962 and have continued till now with 22 M ≥ 5, ~ 200 M ≥ 4 and several thousands smaller earthquakes. It was argued that Koyna is a very suitable site for near field investigations of triggered earthquakes. Discussions were held in dedicated ICDP workshops and finally a go ahead was given. As a precursor to setting up a near field laboratory at ~ 7 km depth, a 3 km deep Pilot Borehole has been completed in June 2017 and investigations are being carried out for necessary input for setting up the deep borehole laboratory. Salient features of this project are also presented.