SKS/SKKS splitting and Taiwan orogeny

We determine 58 sets of splitting parameters, fast direction (φ) and delay time (δt), from broadband SKS/ SKKS waves recorded at temporary and permanent stations in Taiwan. These and earlier results, from S and ScS as well as SKS, show an island-wide pattern of φ alignment with N-NNE structural trends in southern and central Taiwan and then turn smoothly to EW following the structural bight in northern Taiwan. Remarkable differences in δt for eastern and southwestern events are found, resulting probably from a more anisotropic upper mantle in the east, under the Central Range. With δt an average of 1.3 seconds our observations are consistent with the hypothesis that the orogeny involves shear or flow in the upper mantle in central and southern Taiwan. In northern Taiwan, near the ends of the collision and subduction zones, the extrusion and the hydration of olivine may contribute to the orientation of φ.