GPS MEASUREMENTS OF PRESENT-DAY CONVERGENCE ACROSS THE NEPAL HIMALAYA

The high elevations of the Himalaya and Tibet result from the continui ng collision between India and Asia, which started more than 60 millio n years ago(1-4). From geological and seismic studies of the slip rate of faults in Asia(5), it is believed that approximately one-third of the present-day convergence rate between India and Asia (58 +/- 4mm yr (-1)) is responsible for the shortening, uplift and moderate seismicit y of the Himalaya. Great earthquakes also occur infrequently in this r egion, releasing in minutes the elastic strain accumulated near the bo undary zone over several centuries, and accounting for most of the adv ance of the Himalaya over the plains of India. The recurrence time for these great earthquakes is determined by the rate of slip of India be neath Tibet, which has hitherto been estimated indirectly from global plate motions(6), from the slip rates of faults in Asia(7,8), from sei smic productivity(9), and from the advance of sediments on the norther n Ganges plain(10). Here we report geodetic measurements, using the Gl obal Positioning System (GPS), of the rate of contraction across the H imalaya, which we find to be 17.52 +/- 2 mm yr(-1). From the form of t he deformation field, we estimate the rate of slip of India beneath Ti bet to be 20.5 +/- 2 mm yr(-1). Strain sufficient to drive one or more great Himalayan earthquakes, with slip similar to that accompanying t he magnitude 8.1 Bihar/Nepal 1934 earthquake, may currently be availab le in western Nepal.