Shear-wave splitting beneath Yunnan area of Southwest China

Systematic analyses of seismic data recorded by the Yunnan regional seismograph network reveal significant crustal and upper mantle anisotropy. Splitting of the S phase of local earthquakes and teleseismic SKS, PKS, and SKKS phases indicates time-delays from 1.60 ms/km to 2.30 ms/km in the crust, and from 0.55 s to 1.65 s in the upper mantle which corresponds to an anisotropic layer with a thickness about between 55–165 km. The polarization orientations of fast shear waves in the crust are complicated with a predominantly north-south direction, and the mantle anisotropy has a nearly west-east direction. Our results show different deformation styles and mechanisms exist between the crust and upper mantle.