Thickness estimation of Deccan Flood Basalt of the Koyna Area, Maharashtra (India) from inversion of aeromagnetic and gravity data and implications for recurring seismic activity

Thickness estimation of volcanic suite and delineation of underlying Achaean basement topography using geophysical methods have always been a challenging-problem confronting the geoscientific community. In most cases, their estimations are unsatisfactory due to lack of quality dataset or inverse geological situation, where high susceptibility/velocity rocks at the surface are underlain by low susceptibility/velocity rocks. In order to circumvent the above situation, an inversion scheme has been attempted to model aeromagnetic and gravity datasets acquired over the seismically active Koyna region situated over the Deccan Traps of western Maharashtra. Inversion of aeromagnetic data results into a Deccan basalt thickness of about 1500 m below the Koyna region. Further, inversion of gravity data indicates that the entire column of lava below this region is made up of non-massive vesicular type of basalts having a low density of 2.58 g/cm³ and a porosity of about 17%. Presence of vesicles, faults and fractures within the porous basaltic column appears to facilitate the diffusion of fluid in the surrounding medium and in the basement, thus causing the reactivation of faults which may be responsible for recurring seismic activity in this region.