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.