[S02-3] Studies of seismicity at Koyna, India

[S02-3-04] Electrical image of Koyna-Warna seismic zone, India from large scale magnetotelluric studies

^○Prasanta Patro, Ujjal Borah, Kashi Raju, K. Chinna Reddy, Narendra Babu (CSIR-National Geophysical Research Institute, Hyderabad, India)

A major scientific drilling program was launched by Ministry of Earth Sciences, Government of India with an intention to obtain an integrated model which can explain the genesis of reservoir triggered seismicity (RTS) at Koyna-Warna region, India. An exploratory phase covering a suit of geophysical investigations including magnetotelluric studies were carried out preceding to the deep drilling program. More than one hundred broad band magnetotelluric stations were recorded during 2012-14 field campaigns in the Koyna-Warna seismic zone. The apparent resistivity - phase pseudo section along Warna profile delineated a weak zone near Udgiri, coinciding drilling observations. Coast effect and the Dharwarian trend are apparently visible from the Phase tensor ellipses and the induction vector maps. A quick 2D modeling was carried out to the MT data along Koyna and Warna profiles using NLCG approach after rotating the impedances to TE and TM modes. Later, 3D inversion for all the impedance data using WSINV3DMT was carried out for the frequency range 0.01 to 1 s. Modeling results in conjunction with the tectonic of Koyna-Warna seismic zone is discussed.