Electrical structure of the crust below the Deccan Flood Basalts (India), inferred from magnetotelluric soundings

Abstract

SUMMARY The 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.