Deccan Volcanism and Related Seismic Unrest in the Koyna–Warna Region, India

Abstract

Koyna–Warna is a region of low‐tectonic deformation and normal surface heat flow (⁠⁠) in the Deccan volcanic province, India, where low‐to‐moderate magnitude earthquakes have continued to occur in the last 60 yr. These earthquakes are uniquely restricted to an area and confined to the upper crust between 3 and 9 km depth. Located at the last phase of the interaction of India with the Reunion mantle plume ∼65 Ma ago responsible for extensive volcanism, the cause of sustained seismicity in Koyna region is debated. Using the shear‐wave velocity model derived through the joint inversion of the receiver function and surface‐wave data from the seismic zone, we propose that earthquakes in the Koyna region occur due to stress concentration arising because of the high‐density magma intrusions in the shallow crust at 3–9 km. The high‐density mafic‐ultramafic body exerts gravitationally induced stress of about ∼12 to 15 MPa. The continuation of earthquakes in the deeper part is inhibited by the possible fluid‐filled mush zone imaged as a low‐velocity layer at a 9–17 km depth. The magma intrusion as dike can induce a cycle of normal faulting in the overlying rock mass, as observed in the Warna region. We present the first evidence of an extremely high velocity (>4.7 km/s) layer at 40–50 km below Moho, interpreted as the presence of eclogite–peridotite responsible for producing Deccan magma in large volume.