A major national project, “Scientific Deep Drilling in the Koyna Intra-plate Seismic zone of Maharashtra”, has been undertaken for directly measuring the in-situ physical properties of rocks, pore-fluid pressure, hydrological parameters, temperature and other parameters of an intra-plate, active fault zone in the near-field of earthquakes – before, during and after their occurrence. As a part of the ‘Preparatory Phase’, various studies have been undertaken since October 2012. The studies include Broadband Seismology, Magneto-Tellurics (MT), airborne Gravity Gradiometry and Magnetics and LIDAR surveys, etc. These studies were supplemented by exploratory drilling up to depth of ~ 1.5 km in the vicinity of the seismic zone. Out of the 10 planned boreholes, 7 have been drilled so far: Rasati (1522 m), Udgiri (1196m), Kundi (1134m), Nayari (1211 m), Panchgani (1500 m), Ukhalu (1500 m) and Paneri (1500 m). Geophysical logging as well as heat flow measurements has been carried out. Also, borehole seismometers have been deployed in two holes, Rasati and Kundi. The studies have helped to delineate the sub-surface structure around the seismic zone most prospective for scientific deep drilling and fault zone investigations.
Significant results obtained from the investigations carried out so far include absence of sediments below the basalt cover; the thickness of the basalt column and its relation with the surface elevation; and almost a flat topography of the basement. The temperature at the depth of 5 km has been estimated to be around 130 to 150° C. The issues related to the design of the deep bore hole, instrumentation to be deployed, the drilling and the operational plans for drilling, and international collaboration are being addressed.
An international workshop was held at Koyna during May 16-18, 2014 to review the results obtained from preparatory phase and to design the next phase of investigations involving pilot and deep boreholes in the Koyna region. The Workshop was organized by the MoES and co-funded by ICDP. Delegates included 37 scientists from different organizations in India and 12 international experts from fault-zone drilling projects worldwide. The highlight of the Workshop was the lively interactions during three break-out groups, which resulted in finalizing the outline of the drilling and measurements plan in the pilot holes. It is planned to drill and instrument two 3 km pilot boreholes at identified locations in the Koyna-Warna region in the next one and half years, to be followed by detailed design and drilling of the deep borehole(s).
As a part of the project, a Borehole Geophysics Research Laboratory has been set up at Karad, Maharashtra which will serve as the operational centre for carrying out the research activities related to the scientific deep drilling. The laboratory will mainly focus on the borehole geophysics investigations and related research, including core analysis and associated field / research studies.