ИСТИНА

Extensive seismicity data has been generated in the seismically active Koyna-Warna region of Maharashtra, India for the last five decades. Earthquakes continue to occur in the region since early 1960s when the initial construction and impoundment of the Koyna dam began. Prior to this, the region was devoid of any significant seismicity. The largest known M6.3 earthquake in 1967 in the region is the best known example of Reservoir Triggered Seismicity (RTS). Several studies were done to explain triggered earthquakes based on seismicity and reservoir water levels, nucleation process, pore pressure changes, seismic and hydrological precursors. In an earlier Indo-Russian collaborative work, joint experiments on cyclic loading of rock samples for modelling of transient seismic process were carried out at the Geophysical Observatory “Borok” of IPE, Russian Academy of Sciences. Data bases of acoustic emission, loading deformation, speed of elastic waves for the subsequent analysis and interpretation were also generated. All these experiments were conducted on rock samples collected at the surface. Our preliminary results from the Koyna earthquake catalogue revealed variations in seismicity parameters prior to two strong earthquakes to have a pattern of prognostic anomalies typical of tectonic earthquakes. In tectonic earthquakes, unstable conditions in a source zone develop gradually leading to a metastable zone which shows variations in certain seismicity parameters known as prognostic anomalies. In a new project proposed under RSF-DST initiative we intend to take these studies forward by conducting laboratory experiments on core samples obtained from deep boreholes (~1.5km) drilled around seismic source volume between Koyna and Warna reservoirs in a recent initiative of the CSIR-National Geophysical Research Institute, Hyderabad and Ministry of Earth Sciences, Govt. of India. This study provides a unique opportunity to understand physical parameters of fracture process and to compare them with earthquake catalogues to identify factors determining the pattern of induced or triggered earthquakes. Also, the analysis of transient processes is an important part of investigation of the nature of origin and evolution of failure processes in lithosphere. The investigation both in situ and in laboratory allows clarifying the basic properties of the medium and physical mechanisms controlling the dynamics of seismicity.