VORTEX MOTION OF THE CRUST DEFORMATION IN THE TIBETAN PLATEAU AND ITS FORELAND

Since 1996, a regional GPS network has been established along the northern Tibetan Plateau and its neighboring foreland, and has been measured for the period 1996\|1998.* Viewed relative to Chengdu (CHDU fiduciary station representing the stable South China), stations of the northern plateau bounded by the Qilian Shan and the Altyn Tagh fault, move NE to NNW with 20 5～11 7mm/a, and NE to NNE with 10 5～1 5mm/a in its foreland. Addition, the Lhasa (LHAS tracking station in the southern Tibetan Plateau) moves NNE at 23 1mm/a related to CHDU. Especially interestingly, the velocities and the directions of motion vectors of stations in the northern Tibetan Plateau decrease progressively and deflect systematically westward from south to north, respectively. More, the tangents of motion vectors of stations converge around a point near the central of Qaidam Basin except the GLM station at Golmud. We, therefore, find that the general vortex feature of the crust motion appears on the velocity field in the northern Tibetan Plateau. And the anti\|clockwise vortex motion is restricted by block boundaries within the plateau, and also involved the related forelands for example HCY station (Jianyuguan) at the Hexi Corridor.