Because the elastic deformation of rock is fundamental to the earthquake process, geodetic surface measurements provide a measure of both the geometrical parameters of earthquake rupture, and a measure of the temporal and spatial development of elastic strain prior to rupture. Yet, despite almost 200 years of geodesy in India, and the occurrence of several great earthquakes, the geodetic contribution to understanding future damaging earthquakes in India remains minor. Global Positioning System (GPS) geodesy promises to remedy the shortcomings of traditional studies. Within the last decade, GPS studies have provided three fundamental constraints concerning the seismogenic framework of the Indian Plate: its overall stability (<0.01 μstrain/year), its velocity of collision with Asia (58 ± 4 mm/year at N44E), and its rate of collision with southern Tibet (20.5 ± 2 mm/ year). These NE directed motions are superimposed on a secular shift of the Earth's rotation axis. As a net result, India currently moves southward at 8 ± 1 cm/ year. In the next few decades we can expect GPS measurements to illuminate the subsurface distribution and rate of development of strain in the Himalaya, the relative contributions of along-arc and arc-normal deformation in the Himalaya and southern Tibet, and perhaps the roles of potential energy, plastic deformation and elastic strain in the earthquake cycle.
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|Published - Feb 10 1998