Epeirogenic studies in India with reference to recent vertical movements

Abstract

Epeirogenic movements of regional extent have been manifest and recorded in several parts of India from Late Proterozoic to present times through the Tertiary and Recent. The main features of these movements, especially Recent vertical movements, in typical areas in the platform and coastal areas of peninsular India are described and the salient results of the study, qualitative and quantitative, of these zones are outlined. Quantitative measurements of Recent vertical movements have been made largely by geodetic methods and precision levelling in the plateau areas as also in the mobile, orogen zones of the Himalayan and sub-Himalayan tracts and by sea-level measurements through an extensive network of coastal automatic tide-gauge stations. The annual variations of sea level have been studied for several Indian ports. The land uplift or subsidence in relation to mean sea level over the Indian coast has also been studied. The application of geophysical techniques in the identification and delineation of regions of epeirogenic movements has been discussed and illustrated by the results in two type areas, viz., the coastal sedimentary belt of Madras and the vast Deccan Trap territory in western India. In the latter area, blanketed by extensive basaltic lavas over a vast region, the gravity data have brought out a number of major zones of subsidence and uplift which have been corroborated by the results of refraction seismic soundings. One of these major zones of subsidence is in the Koyna region which witnessed a major disastrous earthquake a few years ago. The results of deep seismic sounding along a traverse across the southern part of the Indian peninsula now in progress have also been briefly mentioned. Five important areas have been selected for quantitative measurements of current epeirogenic movements, namely the Shillong Plateau in northeast India, the Chhotanagpur Plateau and Singhbhum region in Bihar, the Aravalli region of Rajasthan, the Narmada Sone Rift in central India and the Deccan Trap territory including the Koyna earthquake zone.