Physical and mechanical properties of rocks before, during and after a quake will be measured
What kind of physical and chemical changes take place in the earth's crust during an earthquake? How does the temperature change and will there be some melting of the rock?
Answers to such fundamental questions are expected from the results of a unique Rs.300-crore project under which scientists will drill a seven-km deep borehole into an earthquake zone for an on-the-spot measurement of various physical and chemical changes.
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.
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” said the project leader, Dr. N. Purnachandra Rao.
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.
Besides, that was up to a depth of three km, “whereas what we are going to get here is the representative earthquakes of the region within a depth of seven kilometres,” Dr. Rao added.
Pointing out that Koyna-Warna region was known for Reservoir Triggered Seismicity (RTS), he said that 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.
“Since there is no other source of seismic activity within 50 km of the Koyna-Warna region, it forms an excellent natural laboratory for earthquake studies,” Dr. Rao said.
Explaining the importance of the project, he said so far scientists have been drawing indirect inference from measurements on the surface of the earth. “We have been measuring from the surface and trying to understand what is happening inside. But now we 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.
“This would help us to plan the exact location for drilling”, Dr. Rao said. While earthquakes normally occur in the crust down to 35 km depth, the drilling could be done only up to a depth of 12 km with the present technology.
Dr. Rao said that most of the earthquakes in that region were occurring within seven km and there was no need to go beyond that depth. Besides, they would be drilling into hard granite rock and the cost of the drilling would go up exponentially as they go down further.
“We are not simply drilling up to seven km. It is going to be a permanent observatory and we will be monitoring for several years,” he said.
Koyna-Warna region was like a laboratory where earthquakes were constantly occurring within a shallow depth range. “It makes it feasible for drilling and setting up an observatory for earthquake studies,” he added.
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.