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

Abstract

AbstractUsing the difference of shear 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) VSH > VSV 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 varies markedly with depth. It is generally very weak in upper crust and upper mantle lid, while it becomes intense in the rheologically weak lower crust and asthenosphere, which indicates the lower crust may take a role of decoupling in the lithosphere deformation. (2) VSH < VSV anisotropy is the main characteristic of the lower asthenosphere beneath 200 km, which reflects the vertical movement of the mantle mass. (3) The overall pattern of anisotropy in eastern China continent is that in stable blocks VSH > VSV anisotropy is more prominent in lithosphere and VSH < VSV anisotropy is weaker in asthenosphere, in tectonically active areas it is contrary. (4) In west China the anisotropy is apparently related with the subduction of India plate beneath Tibetan Plateau. The conspicuous VSH > VSV anisotropy is the result of the collision and compression between India plate and Eurasia continent which causes orientated recrystallization of mantle material.