To study the kind of physical and chemical changes take place in the earth's crust, temperature changes and melting of rocks during an earthquake a unique Rs.300-crore project of drilling a seven-km deep borehole into an earthquake zone for an on-the-spot measurement of various physical and chemical changes has been started. Under the project — Deep Scientific Drilling into Earthquake zone of Koyna-Warna region (Maharashtra) — seismologists and other scientists from the National Geophysical Research Institute (CSIR-NGRI) plan to establish a deep borehole observatory in the seismically-active intra-plate fault zone in Koyna-Warna region. Former NGRI Director and currently a member of the National Disaster Management Authority (NDMA), Prof. Harsh K. Gupta is the advisor of the project. and Dr. N. Purnachandra Rao is the project leader.
Continuous monitoring of this borehole at seven-km depth would enable measurement of physical and mechanical properties of rocks, hydrology, temperature and other parameters in the near-field of earthquakes before, during and after their occurrence. It is expected to lead to a better understanding of the mechanics of earthquake faulting and the physics of reservoir trigger mechanism. He said the Koyna-Warna deep drill hole would be the first of its kind in the world to directly investigate earthquakes in a stable continental crust, unlike the deep borehole drilled on a plate boundary fault In San Andreas Fault in California (whose depth is only 3 km).
Koyna-Warna region is known for Reservoir Triggered Seismicity (RTS). The triggered earthquakes have been occurring regularly in an area of 20 x 30 sq.km ever since the impounding in Koyna reservoir in 1962. While the largest earthquake in that region was of 6.3 magnitude on Richter scale, hundreds of others of varying magnitude have been recorded. So far scientists have been drawing indirect inference from measurements on the surface of the earth. But now they will measure right at the spot. This would be extremely valuable knowledge for whole world and has the potential to facilitate earthquake forecasts in future. A seismic network of 15 sensors operating in the region for the last six years helped the scientists to precisely locate the area where the earthquakes are occurring.
Dr. Rao said NGRI would be installing seismometers, temperature loggers, strain meters (to measure deformities in the rock) and some instruments to measure physical parameters like density all along the borehole at different depths up to seven km. He observed that in plate boundary zones where the earthquakes were usually extensive and deeper, it would be difficult to pinpoint an area for drilling. In a bid to supplement these studies, a new institute, Seismological Research Laboratory was being established by the Ministry of Earth Sciences at Karad, Maharashtra. It is planned to develop into a centre of excellence in earthquake and related studies.
Reservoir Triggered Seismicity
In deep and large reservoirs, the column of water in a reservior alters in-situ stress state along an existing fault or fracture. In these very large and deep reservoirs the load of the water column can significantly change the stress state on the fault or fracture by increasing the total stress through direct loading, or decreasing the effective stress through the increased pore water pressure. This significant change in stress state can lead to movement along the fault or fracture resulting in an earthquake. it has been noted that seismicity appears to occur on dams with heights larger than 100 meters (330 ft). The extra water pressure created by vast reservoirs is the most accepted explanation for the seismic activity