Crust and shallow mantle structure of south India by inverting interpolated receiver function with surface wave dispersion

Abstract

The 3-D shear wave velocity structure beneath south India crust and shallow mantle up to depth 130 km, have been determined from the joint inversion of surface wave dispersion and interpolated receiver function (RF). The P wave RF interpolation helps to equalize the lateral sampling of the RF and the surface wave dispersion, which mainly simplifies the RFs. One of the major difficulties due to back azimuthal variations of receiver functions is suppressed by this scheme of spatial interpolation. We combine the interpolated receiver functions with Rayleigh wave dispersions to estimate the shear wave velocity structure beneath the region. This study reveals the significant variations in crustal thickness and nature of intra crustal layering of southern India shield. The crustal thickness of south India varies from 40 km in Deccan Volcanic Province (DVP), 38 km in East Dharwar Craton (EDC), 44 km in West Dharwar Craton, northern block (WDC-N), 50 km in West Dharwar Craton, southern block (WDC-S), 48 km in Southern Granulite Terrain (SGT) and 38 km in Kerala Khondalite Belt (KKB). The average upper crustal thickness is ∼5 km and that of middle crust is ∼15 km. The lower crust shows significant variations in terms of thickness (varies from ∼8 to 32 km) as well as the high velocity mafic layer. The shear wave velocity variations in the model correlate strongly with the different geological variations along different tectonic blocks of southern India. The DVP, surprisingly, does not have any distinct signature of volcanism in the underlying crust and shallow mantle. The shallow mantle part of entire south India has similar characteristics except for EDC where the velocity is higher beyond 85 km depth.