Scientific Deep Drilling to Study Reservoir Triggered Earthquakes at Koyna, India
The Koyna Dam located close to the west coast of India is the most outstanding example of RTS, where triggered earthquakes have been occurring in a restricted area of 20x30 sq km since the impoundment of Shivajisagar Lake in 1962. These include the largest triggered earthquake of M~6.3 on Dec 10 1967, 22 earthquakes of M>5, about 200 earthquakes of M~4, and several thousand smaller earthquakes since 1962. The RTS was further enhanced by impoundment of the nearby located Warna reservoir in 1993. We use "Koyna" for the "Koyna-Warna" region. The earthquake frequency increases every year following the monsoon rains in the months of June and July; almost every year one or more M~4 earthquakes occur. In the year 2009, the seismic activity has been quite intense and the latest M 5.1 earthquake occurred on 12 Dec 2009. There is no other source of seismic activity within 50 km of the Koyna Dam.
The seismicity in the area has been well documented and the subsurface structure has been probed using multiple geophysical methods. The seismicity distribution during the past ~5 years defines two, about 10 km long relatively narrow (~2 km) and shallow (6-8 km), hypocentral zones in the area. Existing geothermal datasets predict temperatures not exceeding 150°C at a depth of 6 km. In spite of several investigations, the continuing seismicity in the area remains to be comprehended. It is hypothesized that the region was stressed close to critical before the impoundment of Koyna reservoir in 1962. The maximum credible earthquake for the region is M~6.8; it is estimated that more than one half of this energy has been already released since impoundment, and that RTS shall continue for many more years. The occurrence of earthquakes of M>5 is governed by factors like rate of loading, highest water levels reached, duration of retention of high water levels and whether the previous water maxima has been exceeded or not (Kaiser effect).
The continuing seismicity at Koyna for the past 47 years, therefore, provides a unique opportunity to directly measure the physical and mechanical properties of rocks, pore fluid pressure, hydrology, temperature and other parameters of an intra-plate, active, fault zone in the "near-field" of earthquakes - before, during and after their occurrence, in a restricted area and at depths of 6-7 km that can be accessed by drilling with the existing technological expertise. The proposed borehole observatory in this active zone will thus permit direct, continuous monitoring of an intraplate seismic zone at depth, leading to a better understanding of the mechanics of faulting, physics of reservoir triggered earthquakes, and will contribute appreciably to earthquake hazard assessment and forecasting.
(Fig.: Koyna Dam, India, © Google Earth.)
Asia, India, Western India, Maharashtra, Koyna
17° 24' 6'' N, 73° 45' 8'' E (Please scroll down to end of page for more information.)
Project Start and End
- workshop date: March 21 to 25, 2011 in Hyderabad/Koyna, India
- Harsh Gupta, Council for Scientific and Industrial Research, National Geophysical Research Institute, Department of Seismology
- Shailesh Nayak, Ministry of Earth Sciences, Government of India
- Georg Dresen, German Research Centre for Geosciences, Section 4.2, Geomechanics and Rheology
- Sergei A. Shapiro, Free University of Berlin, Department of Earth Sciences, Institute of Geology, Geophysics and Geoinformatics, Seismics Working Group
Drilling, ICDP-2011/00, India, KOYNA, Maharashtra, Reservoir Triggered Earthquakes
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