GPS derived velocity and deformation in the Indian subcontinent
Sridevi Jade
Scientist, C-MMACS, Bangalore-560037
Email: Sridevi@cmmacs.ernet.in
Abstract
GPS studies have been carried out by C-MMACS in the Indian Sub-continent since 1994 to determine the displacement and strain accumulation in the region over the past few years. This paper integrates the results obtained over the years in different regions of Indian subcontinent using GPS geodesy to get an overall picture of deformation and the related interpretations and discussions. The regions covered by C-MMACS are Southern peninsula, Ladakh, Gharwal, Kumaon, Darjeeling Sikkim, Gujarat, Andamans and Shillong. The GPS derived absolute velocity vectors of about 50 sites are given in the ITRF 97 reference frame. Site velocities in Indian reference frame and relative to IISC IGS station are also given Some important comparisons and significant discussions based on the above results are presented. Some significant conclusions that arise from the above study are Southern peninsula to Delhi, moves as a rigid plate with the velocity of Indian plate. All the convergence occurs in the 2500 km stretch of the Himalayan arc from Kashmir to Arunachal and the convergence rates vary significantly from west to east .
Introduction
The Indian plate is bounded by transform boundaries to the east and west and a continental collision boundary to the north and spreading centers to the south west. Persistent collision of the Indian Plate with Eurasia over the past 50 Ma, has made the tectonics of Indian subcontinent very dynamic and complex. Some of the most spectacular geomorphic features of the globe, notably the Himalayas, the Karakoram and the Tibetan plateau which together span a wide deformation zone more than 2,000 km are a result of Indo-Eurasian collision. The southern limit of this zone of compressive intercontinental deformation is dramatically marked by a smooth circular arc of the Himalayan fold and thrust belt that rises abruptly over the under thrusting, yet barely deformed, Indian plate. Both the geological structure and active tectonics of this belt seem to vary little along the 2500 km stretch of the Himalayan arc from Kashmir to Arunachal, testifying to a remarkably uniform deformational style throughout. These grand expressions of the Indo-Eurasian collision processes still operating in the convergence zone, mark the region as being potentially the most diagnostic for modelling them. For, an understanding of these processes that drive and absorb collision, is crucial to reconstructing the evolution of older collision systems which have fashioned the continents through geological time.
Several studies over the past quarter century led to the recognition that a substantial part of the Indo-Eurasian convergence is absorbed by the over thrusting of India's fractured leading edge onto itself, a process that raised and sustains the mighty Himalayas, creating every few hundred years a series of great earthquakes from west to east. The Indian subcontinent is one of the most earthquake prone areas of the world. Several great earthquakes have occurred at the plate interiors and boundaries in this subcontinent during the last two decades causing massive losses. Primary objective at CMMACS is to generate insightful understanding of deformation mechanism in the plate interiors and also the boundaries which is the major cause of earthquakes . This can be achieved by using multi disciplinary tools to observe, measure and understand deformation mechanism related to stresses at all scales. This would result in better understanding of processes that drive destructive natural phenomena as earthquakes. GPS gives the physical measurement of deformation field and velocity in any region to a reasonable accuracy which forms the key input in the quantification of earthquake hazard. GPS studies were carried out by different groups in India with foreign collaboration ( J Paul et. al. , 1995, 2001 ; Freymeuller et. al, 1996; Bilham et. al, 1998; Larson et. al , 1999; Sridevi et. al., 1999, 2001, 2002; Bilham and Gaur, 2000; Reddy et. al, 2000; Bilham et. al., 2001; Banerjee and Burgmann, 2002.) in different regions of the Indian Subcontinent. This paper presents the results of the GPS studies carried out at C-MMACS in Southern peninsula, Ladakh, Gharwal and Kumoan, Darjeeling Sikkim, Gujarat, Andamans and Shillong regions since 1994 till date to give significant insights in to the deformation mechanism in the Indian subcontinent. The style of regional deformation using GPS has been studied in detail in specific regions of Southern peninsula, Ladakh, Gharwal, Kumaon and Gujarat using campaign style GPS measurements and the results have been published ( J Paul et. al. , 1995 , 2001; Sridevi et. al. 1999, 2001, 2002;) . The results presented in this paper lay emphasis on the absolute and relative motion of all the GPS sites measured by C-MMACS both campaign style (short period observations) and permanent (long period observations) to give insight in to the motion across the Indian plate.
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