Anisotropy in Crust and Upper Mantle Beneath China Continent and Its Adjacent Seas

Using the difference of S wave velocity structures derived respectively from Love and Rayleigh waves, the polarization anisotropy in crust and upper mantle beneath China continent and adjacent seas is studied. The result indicates that the distribution of anisotropy is spatially uneven. (1) The V-SH > V-SV anisotropy is dominant in the upper 150 km, which indicates that the horizontal stress in shallower lithosphere and the horizontal mass flow in upper asthenosphere are the leading factors in the formation of polarization anisotropy. In the land area the anisotropy intensity changes markedly with depth. The anisotropy in upper crust and upper mantle lid is generally weak, while the anisotropy is intense in the rheologically weak lower crust and asthenosphere, which indicates that the lower, rust may decouple in the lithosphere deformation. (2) V-SH < V-SV anisotropy is the main characteristic of the lower asthenosphere beneath 200 km, which reflects the vertical movement of the mantle mass. (3) The overall picture in eastern China continent is that in stable blocks V-SH > V-SV anisotropy is more prominent in lithosphere and V-SH < V-SV anisotropy is weaker in asthenosphere, in tectonically active areas it is on the contrary. (4) In western China the anisotropy is apparently related to the subduction of India plate beneath Tibet. The conspicuous V-SH > V-SV anisotropy is the result of the collision and compression between India plate and Eurasian continent which makes the mantle material recrystalize in preferred orientation.