Monday, 21 March 2011

Koyna dam-triggered earthquakes: NGRI-CSIR to dig a 7 km bore into the earth

Syed Akbar
Hyderabad, March 21: Indian geophysicists will make a deep bore hole, seven km into the earth, for a first hand understanding of the mechanism that triggers earthquakes.

The deep bore hole, first of its kind facility any where in the world, will provide clues to earth and earthquake scientists about physical, geological and chemical processes and properties of the earthquake volume in real time. The experiment will also throw light on what causes the earth to quake in regions, which are otherwise "stable" or quake-free.

The city-based National Geophysical Research Institute (NGRI-CSIR) has selected Koyna in Maharashtra for the study as the region has been witnessing "artificial water reservoir triggered earthquakes" for almost 40 years. The department of earth sciences will spend 60 million US dollars on the project.

"In Koyna region, earthquakes occur in a very small area of 20 km x 30 km. This provides an opportunity to investigate the physics of earthquakes in a very accessible area. There's, however, no other known source of earthquakes within 50 km of the Koyna dam," NGRI-CSIR distinguished scientist Dr Harsh Gupta told this correspondent.

According to NGRI-CSIR director Dr YJ Bhaskar Rao, the experiment is expected to significantly extend the understanding of the origin of earthquakes in the region. "Our scientists have seen that earthquakes of about 4 magnitude are preceded by nucleation (vapour bubbles) lasting 200 to 300 hours. Identification of the nucleation in real time has led to short time forecast of earthquakes of about 4 magnitude," he said.

Koyna is a classical site of reservoir triggered seismicity. Earthquakes have been occurring in Koyna since the impoundment in 1962, including the largest reservoir-triggered one of 6.3 magnitude on December 10, 1967. The region has thus far witnessed 20 earthquakes of magnitude greater than 5 and several thousand smaller ones.

Dr Harsh Gupta said a deep bore hole would provide direct observational data on several vital issues relating to earthquakes, and contribute to earthquake hazard reduction. The experiment will help answer questions related to the genesis of reservoir triggered seismicity.

At present geophysicists do not have much knowledge about the physical properties of rocks and fluids in the fault (earthquake) zones and how they affect the build-up stress for extended period. This because they do not have data from the near field region.

The deep bore hole will allow direct characterisation of the underground fault geometry, physical properties of rocks, hydraulics, fluid composition and heat flow, as well as throwing new light on the upper crustal rocks and Deccan Volcanic Province.

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