Seismic Anisotropy Beneath Northeast China Revealed by Shear-wave Splitting Analyses

Abstract:

A total of 993 pairs of shear wave splitting parameters obtained using the SKS, SKKS and PKS phases recorded by 183 broadband seismic stations in northeast China demonstrate systematic spatial and azimuthal variations, and therefore provide important constraints on the characteristics of mantle deformation and the direction of asthenospheric flow. Most of the fast orientations are consistent with the relative motion direction between the Erasian and Pacific plates. Results of anisotropy depth analyses suggest that the observed anisotropy mostly resides in the lithosphere-asthenosphere coupling area. Based on the splitting measurements and previous seismic tomography studies, we propose a model in which the observed anisotropy is mainly controlled by mantle flow resulting from the northwestwards subduction of the Pacific plate beneath Eurasia. For some local areas, anisotropy might be related to different mechanisms, including a possible tearing of the Pacific plate that leads to the splitting parameters observed beneath the Jiamusi massif, partial lithospheric delamination beneath the Songliao Basin, and two-layer anisotropic structure in the vicinity of the Yanshan belt.