NGRI to drill 7 km deep borehole
Hyderabad : Hydcerabad-based National Geophysical Research Institute will take up drilling of borehole running into seven kilometres inside the earth in the seismic zone near Koyna reservoir in Maharashtra, as part of its study to understand earthquakes.
A unique study is being carried out for the first time by the NGRI with the support of Ministry of Earth Sciences (MoES), by putting instruments deep inside the earth close to an earthquake-prone zone in Koyna, Maharashtra.
They will measure the changes that occur before during and after an earthquake. As a prelude to this, the seismic zone will be monitored by borehole seismometers at 1.5 km depth surrounding the earthquake zone, enhancing the detectability and accuracy of earthquake locations.
The NGRI is currently carrying out several experiments under this prestigious flagship programme of MoES, the first of its kind in the world, in which they are planning to drill a deep borehole down to 7 km depth inside the earth in the seismic zone near Koyna.
This region is famous for the Koyna dam where earthquakes have been occurring for the last five decades connected with reservoir triggered mechanism.
'Work on this prestigious programme has already begun with 7 out of the total 10 bore holes being drilled and the eighth one is underway in the seismic zone,' said Dr N Purnachandra Rao, Senior Principal Scientist at NGRI leading the research.
He said that finally a deep borehole observatory will be set up for constant monitoring for several years. The study will help scientists understand the earthquake process and to draw inferences from deep down the earth compared to the conventional methods of placing instruments on the earth's surface.
This would be for the first time that scientists will be able to visualize and measure rock changes directly near an earthquake source in an intra-plate zone.
'This will give a direct measurement of what happens near an earthquake fault zone and we can monitor changes in physical properties of rocks deep down in the earth, like changes in density, pressure, temperature,' the scientist said.
'The current study is targeted on intra-plate regions, i.e. inside the plate, and Koyna happens to be one such region which is also considered as a classic example of reservoir triggered seismicity' he said.
Stating that there are many technical reasons to chose Koyna, the main reason is the continued occurrence of earthquakes over the last 50 years at shallow depths reachable by the present day drilling technology.
Besides NGRI, several organizations from India and abroad are likely to participate in this exercise initiated and supported by the Ministry of Earth Sciences.
The Central government has sanctioned about Rs 473 crores for this mega project and a foundation stone for setting up an institute for the purpose has been laid in the city of Karad close to the study region.
Right now, the programme is under preparatory phase where a large number of studies are being carried out to get the required scientific information which will be essential prior to starting the deep drilling programme.
Drilling of a set of bore holes going down to 1.5 km depth surrounding the seismic zone has been taken up and 7 out of 10 bore holes have been completed.
The scientists will put seismometers in the boreholes and this will be the first network in the world where a seismic zone will be monitored by deep borehole seismometers surrounding the seismic zone. The borehole seismometers at depth are very sensitive and will be able to pick up extremely small earthquakes which cannot be recorded otherwise.
The seismometers will be able to detect the exact location so that scientists can plan the most suitable location for deep drilling. In addition, scientists will be able to take up study of the physico-chemical properties of water at different depths to understand how the flow patterns of water and reservoir loads on the surface are connected with earthquake occurrence.
Further, a detailed study of the structure for the entire Koyna region in three dimensions using a large number of scientific methods is underway.
Two air borne surveys have been completed using which scientists have been able to measure for the first time in the country, the gravity field gradients and how these vary in the entire region.
The other airborne survey called the LiDAR, has also been completed, which gives an accurate mapping of the earth's surface, i.e. the surface geomorphology.
This is important since with the vegetation coverage and inaccessibility of the forest regions it becomes difficult to see the bare earth surface and the large number of fine scale lineaments, faults and other features, which will be prove useful in interpretations later on.
'An offshoot of this entire study is that for the first time the world will be able to see how the Deccan volcanic rocks in this region look like at such a depth, and new understanding of the 60 million year old volcanic eruption that shook the earth will emerge by studying these rocks' Dr. Rao added.
News Posted: 24 June, 2014
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