Shear wave splitting across the Ailao Shan‐Red River fault zone, SW China

Abstract

A broad band seismic array was set up across the Ailao Shan‐Red River (ASRR) fault zone, SW China. The shear wave splitting parameters on SKS and SKKS phases are calculated using the method of Silver and Chan (1991) and indicate the polarization direction of 105 ± 6° and the delay time of 1.68 ± 0.44 s beneath the ASRR fault zone. Combined with previous studies, the average polarization direction is 110 ± 19° and the delay time is 1.58 ± 0.44 s to the SW side of the fault, while the values are 83 ± 30° and 1.29 ± 0.29 s to the NE side. This result implies that the upper mantle anisotropy to two sides of the ASRR fault zone are different. Compared with the SE polarization direction observed in the P‐S phase and the N‐to‐S surface movement in GPS data, our results suggest decoupling of the crust and upper mantle beneath the study region.