Present-day kinematics of Asia derived from geologic fault rates

Active fault geometry, available Quaternary rates on major faults, and the far-field plate motion are used to determine crustal kinematics in the collision zone between India and Asia. Using a finite element formalism to construct a spherical shell model of the Asian continent with embedded faults, we seek a velocity solution approaching the motion of rigid blocks by minimizing the elastic strain energy in the fault-bounded blocks. By doing so, we test the assumption that long-term deformation within continents in mostly localized into major faults. In the solution, fault motion accounts for more than 80% of the deformation, allowing us to describe our velocity model in terms of quasi-rigid block rotations on the sphere. South China is rotating clockwise about a pole located southwest of Borneo, implying an E-ESE velocity vector of -11 mm/yr for a point at Shanghai, in agreement with the velocity vector determined by very long baseline interferometry [Heki et al., 1995]. The eastward movement of south China is accommodated by oblique extension along the Red River fault at a rate of 10+/-5 mm/yr in the south and by the combination of left-lateral strike-slip motion on the Qinling-Dabie Shan fault and the counterclockwise rotation of the Ordos and adjacent blocks in the north. The Tarim rotates clockwise with respect to Dzungaria about a pole located at 44 degrees N, 92 degrees E, consistent with increasing crustal shortening toward the west throughout the Tien Shan. Assuming incompressibility, a crustal volume budget over a domain encompassing the Tertiary mountain ranges in Asia shows that, over the last 10,000 years, 73+/-4% of the north-south shortening between India and Asia has been absorbed by thickening of the lithosphere, and 27% has been accommodated by lateral extrusion of continental blocks. The present-day predominance of thickening in Asia results from the relatively slow eastward motion of south China, controlled by strike-slip faulting in the Qinling Shan and oblique extension in northeastern China.