[S02-3] Studies of seismicity at Koyna, India

[S02-3-01] Artificial Water Reservoir Triggered Earthquakes at Koyna, India

^○Harsh K Gupta (National Geophysical Research Institute, Hyderabad, Telangana, India)

invited

Koyna, near the west coast of India is the most prominent site of artificial water reservoir triggered seismicity (RTS). Soon after the impoundment of the Koyna Dam in 1962, RTS was observed. It has continued till now. It includes the largest RTS earthquake M 6.3 on December 10, 1967; 22 M≥5.0, and thousands of smaller earthquakes. The entire earthquake activity is limited to an area of about 30 km x 20 km, with most focal depths being within 6 km. There is no other earthquake source within 50 km of the Koyna Dam. An ICDP Workshop held in March 2011 found Koyna to be the most suitable site to investigate reservoir-triggered seismicity (RTS) through deep drilling. Studies carried out in the preparatory phase since 2011 include airborne magnetic and gravity-gradient surveys, MT surveys, drilling of 9 boreholes going to depths of ~ 1500 m and logging, heat flow measurements, seismological investigations including the deployment of six borehole seismometers, and LiDAR. The Second ICDP Workshop held during 16-18 May 2014, reviewed the progress made and detailed planning of putting the borehole observatory was discussed. With improved location of earthquakes using the borehole seismic stations, the errors in hypocentral parameters have been brought down to ± 300m. The site of a 3 km deep pilot borehole was debated and among the 5 possible location, based on the seismic activity and logistics the location of the first Pilot Borehole has been finalized and the drilling has started.