3:00 PM - 4:00 PM
[S21-P-06] The shear-wave splitting in the crust and the upper mantle around the Bohai Sea, North China
Bohai Sea area is a significant area with intense deformation in the eastern North China Craton, where experienced thermotectonic reactivation and destruction during the Late Mesozoic–Cenozoic. In order to infer the distribution of local stress and the deep geodynamic process in North China, this study detects first-order seismic anisotropy in the crust and upper mantle beneath Bohai Sea area. We collected local earthquakes within ML4.0 around Bohai Sea area and teleseismic events with magnitude greater than Ms5.5 between August 2007 to July 2012 by shear-wave splitting system analysis method and the grid searching method of the minimum tangent energy to measure the anisotropic parameter. The total 535 local shear-wave and 726 XKS splitting measurements were obtained from stations involving permanent regional seismograph networks and a temporary seismic network. The dominant orientation of local shear-wave splitting in the curst is nearly East-West, which suggests the direction of local maximum compressive stress around the Bohai Sea area. The nearly North-South orientation of polarization caused by structure anisotropy was obtained at some stations, which located at the Tan-Lu fault belt and Zhang-Bo seismic belt. The average polarization of XKS-splitting is 87.4o from north to east. The average time-delays of XKS-splitting range from 0.54 s to 1.92 s, it suggests possibly about 60 km to 210 km thickness of the anisotropic layer. The measured results indicate the upper mantle anisotropy beneath Bohai Sea area, even the eastern of North China, is mainly driven by asthenospheric mantle flow from the subduction of the Pacific plate. From the complicated anisotropic characteristics in this study, we infer that there might be multiply complex mechanism in the crust and upper mantle around the Bohai sea area.