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S U M M A R YThe Indian shield has experienced major stable continental region (SCR) earthquakes in the recent past, which occurred in the Deccan Volcanic Province. Until now the deeper crust below the Deccan traps, where thick basaltic layers cover large areas of the Indian shield, remains poorly understood. A magnetotelluric (MT) study covering a broad period range was conducted along a N-S running profile of 330 km length to achieve more insights into the nature of the crustal electrical structure below the flood basalts. After dimensionality analysis and decomposition, 2-D inversions for TE and TM modes were carried out. The basalt cover, characterized by at first glance surprisingly low electrical resistivities, is found to have an average thickness of 400 m with the exception of central parts of the profile where it reaches up to 700 m. The crust is in general highly resistive, but several subvertical zones of enhanced conductivity were delineated in the middle-to-lower crust, which are tentatively explained as images of hidden, partly reactivated faults/fractures of the Precambrian basement. Sensitivity analysis indicates a high resolution of these features. An alternative approach incorporating macro-anisotropy is additionally considered and corresponding 2-D anisotropic forward modelling confirms the existence of successions of conductive dykes in the deep crust.

We present here the results of magnetotelluric (MT) studies carried out along a 330 km long NE‐SW trending traverse from Daulatabad at the northeastern end to Koyna on the southwestern end across the Deccan volcanic province (DVP) in western India. The 2‐D MT modeling results obtained along this traverse together with those from other MT traverses in this area are examined and integrated with the results from deep seismic sounding, 3‐D teleseismic tomography, and heat flow studies. The deep geoelectric section as deduced from MT models point out to a two layered lithospheric mantle structures with an upper very high‐resistive layer (several thousands of ohm m) and a bottom relatively conductive one (a few tens of ohm m to a few hundred ohm m). The lithospheric electrical structure is inferred to be linked to compositional changes associated with a depleted lithospheric upper mantle in the Dharwar craton. An impressive feature that the study has brought out is the presence of a well‐defined lithospheric upper mantle conductor in the depth range of 80–120 km limited to the middle segment of the MT traverse from Sangole to Partur over the DVP. The electrical characterization of the region including the presence of upper mantle conductor shows close similarities with that of other similar cratonic regions like the Slave and Superior cratons in northwestern Canada.

A set of geophysical measurements and observations was undertaken to investigate the nature of the crust beneath the epicentral region of the deadly Mw 6.1 Latur earthquake of September 30, 1993. With an estimated focal depth of 2.6 km and the associated well defined but subtle surface ruptures, it is a rare stable continental region (SCR) earthquake with surface rupture. The focal depth of 69 out of 73 well located aftershocks is less than 5.5 km. Broad band (10³–10−3 Hz) magnetotelluric (MT) soundings reveal the presence of an anomalously high conductivity zone at a shallow depth range of 6–10 km. Consistent with this result is the observation of a Pc phase, lagging behind the Pg phase by about 0.6 to 0.8 sec in the aftershock seismograms indicating a low velocity layer (LVL) at 7 to 10 km depth. A Bouguer gravity low of 5 m.gal, nearly coincident with this feature, is also observed. Above evidences indicate that the focal zone of the Latur earthquake sequence is limited to depths of about 5 to 6 km in the upper crust by an underlying low‐velocity and high conductivity layer. We interpret this high conductive, low velocity layer as a fluid filled fractured rock matrix. The inferred stress regime, including due to uplift of the Deccan Plateau, triggered by erosion of basalt cover is likely to be confined mostly in the upper part of the crust. Existence of a low velocity, high conductivity fluid filled layer will enhance stress concentration in the uppermost brittle part of the crust causing mechanical failure.