SKS wave splitting study of the transition zone at the central portion of the North China Craton

SKS wave splitting analysis is performed to image the upper mantle anisotropy on the teleseismic data recorded by Peking University temporary seismic arrays and several permanent seismic stations in the transition zone at the central portion of the North China Craton (NCC). Weak seismic anisotropy is observed inside the Ordos block with delay times less than 0.7 s. The delay times in the eastern margin of the Ordos block, including the Shanxi Basin, Taihang mountain and the North China plain are larger than 1.0 s, showing strong anisotropy in the upper mantle. The ENE fast polarization directions in the Taihang mountain are significantly different from the E-W to ESE fast polarization directions in the Ordos block and the North China plain to the west and east. As the transition zone of the eastern and western NCC, the variation of the upper mantle anisotropy in the Taihang mountain may reveal a local asthenospheric flow around the southeastern corner of the Ordos block, induced by the anticlockwise rotation of the Ordos block and the eastward asthenospheric flow along the Qinling-Dabie orogen from the northeastern Tibetan Plateau.