Scientists have found a granite basement less than a kilometre below the Deccan Traps near the Koyna dam in Maharashtra, as they plan to study the seismic activities in the region.
"There are no sedimentary rocks at the place we drilled the borehole. We hit the granite basement after drilling through 933 meters thick Deccan Traps," Shailesh Nayak, Secretary, Ministry of Earth Sciences told PTI here.
A team of scientists have drilled a 1.5 kilometre deep borehole near the Koyna dam, the first of four such boreholes, as part of a Rs 500 crore project to monitor tremors and other seismic signatures of impending earthquakes.
Nayak said the cores recovered from the borehole have so far revealed a flood basalt pile comprising several layers of lava flows.
"The transition from basalt to granite is marked by the occurrence of quartz and pink feldspar, followed deeper by typical, coarse grained granite. No infra-trappean sediments have been observed," he added.
Nayak observed that the absence of sedimentary rocks indicates that the area was not under the sea and also rules out possibility of oil reserves.
The drilling is being carried out as part of a major scientific programme funded by the Ministry of Earth Sciences to investigate seismicity in the Koyna-Warna region.
Scientists from a number of institutes including the Pune University, Benares Hindu University, National Geophysical Research Institute, Geological Survey of India are involved in the study.
Three more bore-holes are planned to be drilled in the area before scientists embark on drilling a 8 km deep borehole which will be laced with sensors that pick up chemical, electrical and gravitational signals.
As part of the scientific programme, a research laboratory is also scheduled to come up at Karad near Satara in Maharashtra to study borehole geophysics, Nayak said.
The Koyna region, which is home to a several hydel project, is a highly active seismic zone and would provide scientists an opportunity to study earthquakes more closely in real-time and also help them in looking for precursors or warning signals to predict earthquakes.
Scientists believe that the seismicity associated with the Koyna reservoir was unique in the world as it is one of the few sites where earthquakes of magnitude greater than five continue to occur even four decades after the initial spurt of activity in 1967.
