Deep seismic sounding experiments in the Koyna RTS region: An overview of the results

Abstract

The Koyna earthquake (M 6.3) of reservoir triggered seismicity (RTS) nature took place five decades back on December 10, 1967 in the Deccan Trap covered region of western India. This prompted a large number of both Indian and international geo-scientists to undertake various studies, particularly passive seismological studies with full vigour. In addition to these, active seismic studies, then known as deep seismic sounding (DSS), were carried out across and near the Koyna epicentral region to delineate the crustal velocity structure and geotectonic features of the region. Data acquisition along two DSS profiles was undertaken during 1975–78. The results of such rarely undertaken studies were widely utilised by the global earth scientists. Here we relook at the results published since 1981, and try to assess the global impact of DSS study on the research output during the last four decades. After giving a brief summary on the data acquisition, processing and results, we provide relevant information such as the Trap thickness, basement configuration, regional crustal and subcrustal velocity structures, and deep seated features like faults with a view to relate with earthquake activities. Some concluding observations have also been made discussing the accuracy and likely validity of the DSS results, obtained using the then acquired data and processing methods, and unlikely reprocessing of the data using upgraded tools. New active experiments in the Koyna region are being suggested, particularly to decide about the proper locations of the deep geophysical boreholes down to the hypocenters on the ‘mapped’ faults.