Koyna: Drilling into the rupture zone of a reservoir-triggered magnitude 6 earthquake

Der Koyna-Staudamm, dessen Wasserauflast in der Vergangenheit Seismizität mit Magnituden bis zu 6.3 erzeugt hat. Foto: M. Bohnhoff, GFZ

16.01.2015: The Koyna drilling project in India aims at drilling into the rupture zone of the 1967 M6.3 earthquake, the largest ever recorded reservoir-triggered earthquake that caused 200 fatalities. Until today an increased seismicity rate with annually hundreds of earthquakes of up to magnitude 5 is observed below the co-located Koyna and Warna water reservoirs. Prof. Marco Bohnhoff, group leader for ‘Experimental and Borehole Seismology’ at GFZ has now been selected to become co-Principal Investigator of this pioneering project.

Currently, ten boreholes are drilled down to below the Dekkan flood basalt at 1.2 - 1.5 km depth under the leadership of Prof. Harsh Gupta from the Indian National Geophysical Research Institute. Those holes sample the rock formation and will be instrumented with borehole geophones. The following step will involve drilling two 3.5 km deep pilot holes into the seismically active target zones below the Koyna and Warna reservoirs following the concept of the KTB and SAFOD drilling projects. A full proposal for this part of the project has now been submitted to the International scientific Continental Drilling Programme ICDP.

Once the pilot holes are drilled and instrumented it is planned to drill two main holes into the earthquake rupture of the M6.3 event at roughly 6 km depth in 2016. This most challenging project is expected to provide unrivaled in-situ recordings in order to disclosure processes related to earthquake nucleation and generation.