CURRENT CRUSTAL MOTIONS IN NEPAL AND SOUTHERN TIBET

Repeated GPS surveys in Nepal and southern Tibet provide a direct measurement bf current crustal motions. GPS surveys have been carried out in the region by U. S.,Nepalese and Chinese scientists since 1991.We have measured(17?3)mm/year of contraction between sites in southern Tibet and stable peninsular India,concentrated in a north-south wne 120 km wide at the surface. GPS and leveling observations are consistent with an abrupt transition from a slipping to locked interface at a depth of about 20 kin. We infer India to be underthrusting Tibet at a rate of(20?3)mm/a, and predict additional elastic deformation north of our network.East-west extension of southern Tibet is observed at a,rate of(6?3)mm/year between Lhasa and the Mt. Everest region, and(12?3)m/a relative to western Nepal. This rate is consistent with a simple model in which the Tibetan overthrust wedge extends to maintain arc-norrrial slip vectors all along the Himalayan arc. Additional measurements to be carried out over the next three years will refine these models and extend the spatial extent of our measurements to include more of the Tibetan plateau.