Contemporary Crustal Deformation Around Southeast Borderland of Tibetan Plateau

We derive horizontal velocity field in the southeast borderland of Tibetan Plateau using GPS data collected from the Crustal Motion Observation Network of China between 1998 and 2001. Our result shows a complex spectrum of deformation field in the region. The crust is fragmented into tectonic blocks of various sizes, separated by strike-slip and transtensional faults. Being driven mainly by eastward extrusion and gravitational buoyancy force from the west and resisted by stable south China block to the east, the region south and west of the Xianshuihe-Xiaojiang fault system turns from eastward to southward motion, resulting in a cluster of clockwise rotation for its internal sub-blocks. Most noticeable regional deformation includes: 9-10 mm/yr left-slip across the Xianshuihe fault, ∼7 mm/yr left-slip across the Anninghe-Zemuhe-Xiaojiang fault, ∼4 mm/yr NW trending right-slip shear deformation around the south segment of the Lancang River fault, ∼3 mm/yr left-slip across the Lijiang fault, and 5-6 mm/yr right-slip across a deformation zone located ∼150 km northwest of and in parallel with the Longmen Shan fault. There is no noticeable deformation across the southern segment of the Red River fault; instead, the fault seems to be cut orthogonally by a shear zone which is continued south-southeastward from the Xiaojiang fault with ∼6 mm/yr left-slip across. Our results overall are more consistent with predictions of dynamic models assuming a weak lithosphere, particularly the lower crust, than that assuming a strong lithosphere of Tibet.