Seismicity in the peninsular Indian shield: Some geological considerations

The Peninsular Indian Shield, traditionally considered a stable continental region, underwent significant changes in its crustal character, first during the Jurassic break-up of Gondwanaland, and then through the process of underplating as the cratonic block moved over the plume heads during its northward journey. The breakup resulted in the development of a series of fractures appearing as lineaments on the surface, while the underplating caused subcrustal magmatism as well as surface volcanicity. The reconstituted Indian crust undergoes heterogeneous deformation responding to the northeasterly stress presumably resulting from ocean opening along the Carlsberg Ridge-Rift system. The deformation is comparable to block tectonics, in which movements are restricted to the boundaries of the blocks, while internally these remain rigid. In the context (if the Peninsular Indian Shield, the relative movements of rigid blocks trigger earthquakes. The presence of fluid in the deforming medium facilitates movement. There can be several sources of fluid release, influx from the subcrustal magma body or through some deep crustal processes like dehydration metamorphism. In some special instances, water leaking from a reservoir can help trigger earthquakes.