high-quality magnetotelluric data at 100 stations, provide both regional information about the thickness of the Deccan Traps and the occurrence of localized density heterogeneities and anomalous conductive zones in the vicinity of the hypocentral zone. Acquisition of airborne LiDAR data to obtain a high-resolution topographic model of the region has been completed over an area of 1,064 km 2 centred on the Koyna seismic zone. Seismometers have been deployed in the granitic basement inside two boreholes and are planned in another set of six boreholes to obtain accurate hypocentral locations and constrain the disposition of fault zones.

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The Koyna-Warna region is a premier site of reservoir-triggered seismicity in the Deccan volcanic province of western India. In the present study, shear-wave velocity structure of this region down to a depth of 10 km is estimated using the ambient noise correlation technique with data from a network of 11 seismic broadband stations. Asymmetric Green's functions are obtained that are suggestive of an anisotropic distribution of noise sources in the Indian subcontinent. Cross correlation of continuous noise data of 12 months duration, recorded on the vertical components, enables computation of group velocity dispersion curves from the Green's functions. This is supplemented by Rayleigh waves from local earthquakes, which, in addition to those from noise data, are inverted for the shear-wave velocity structure using the multiple-filter technique. The study reveals on an average, a 0.8 km thick basaltic layer of the Deccan traps with a shear-wave velocity of about 3:0 km=s on the eastern side of the escarpment. A low-velocity, possibly weathered granitic layer with a velocity of 3:3 km=s is found below the traps and is underlain by the granitic basement with a velocity of 3:6 km=s. Except for the surface topographic undulation, the velocity structure in this region, down to 10 km, is similar on either side.

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New empirical relations are derived for source parameters of the Koyna-Warna reservoir-triggered seismic zone in Western India using spectral analysis of 38 local earthquakes in the magnitude range M L 3.5-5.2. The data come from a seismic network operated by the CSIR-National Geophysical Research Institute, India, during March 2005 to April 2012 in this region. The source parameters viz. seismic moment, source radius, corner frequency and stress drop for the various events lie in the range of 10 13 -10 16 Nm, 0.1-0.4 km, 2.9-9.4 Hz and 3-26 MPa, respectively. Linear relationships are obtained among the seismic moment (M 0 ), local magnitude (M L ), moment magnitude (M w ), corner frequency (fc) and stress drop (Dr). The stress drops in the Koyna-Warna region are found to increase with magnitude as well as focal depths of earthquakes. Interestingly, accurate depths derived from moment tensor inversion of earthquake waveforms show a strong correlation with the stress drops, seemingly characteristic of the Koyna-Warna region.