We present the first evidence for a lower S-wave velocity (Vs ~3.3 to 3.5 km/s) at 8-17 km depth underlying a 4 km thick high-velocity zone with Vs >3.8 km/s beneath the west coast and the neighbouring parts of the Deccan Volcanic Province, India, coinciding with the last phase of volcanism. The velocity structure is derived from joint inversion of receiver function from 9 seismographs operated along ~106 km long W-E profile with the surface wave dispersion data. The low-velocity layer possibly represents the horizontally elongated frozen magma reservoir, the source for the magma eruption at ~65 million years produced due to the interaction of the Reunion hotspot with India. The shallow, high-velocity layer could be basaltic mafic intrusions responsible for the production of massive CO2 degassing. The Moho deepens beneath the west coast to ~45 km due to 10-15 km of underplating as a consequence of magma upwelling.