Recent crustal movements and intra-plate earthquakes in India

Abstract

The peninsular shield of India in the interior of the Indian Plate is characterized by intra-plate earthquakes. The major earthquakes in the peninsula are associated with prominent fault zones in the margins of the peninsular shield, especially along the Bombay—Ratnagiri coast, the western parts of the Narmada Rift zone and the southeastern parts of the Precambrian shield. Mild seismicity is also observed in several parts in the interior portions of the shield. Prominent recent crustal movements have been observed in the peninsular shield as evidenced by surface geologic and geomorphic features as well as prominent features in the lineament maps, including aeromagnetic lineaments. While the major intra-plate earthquakes are associated with tectonic zones characterized by deep crustal faults, the mild seismicity in the interior of the shield is associated with epeirogenic movements involving the movement of crustal blocks. The regional gravity and magnetic maps of the Deccan-trap region of the shield indicate prominent zones of uplift and subsidence involving the crust. The movements and dislocation with time in the deeper parts of the crust in the major zones of subsidence, as typified by the Koyna earthquake region which is bounded by a major fault zone on its west, obviously also involve displacements in the superincumbent mass of the Deccan trap. This latter being of much higher density and magnetic susceptibility, causes appreciable changes in the observed gravity and magnetic fields on the surface in addition to surface level changes observed by high-precision geodetic levelling. These studies are now in progress as an aid for earthquake prediction. The role of thermal processes in the upper mantle in these crustal movements is also discussed.