Rayleigh wave phase velocity and azimuthal anisotropy in the central and western North China Craton and surrounding areas
We have obtained high-resolution Rayleigh surface wave phase velocity and azimuthal anisotropy maps at periods of 14～100 s in the central and western North China Craton and its surrounding regions from Eikonal surface wave tomography.The surface wave data comes from the dense portable stations of ChinArray and permanent stations of China National Seismic Network.The results show that there exhibits a wide range of high-velocity and weak anisotropy in the Ordos Block at periods of 20～100 s,but the anisotropy is strong in the southwest of this block,and it can extends eastward to 108°E.The results indicate that the lithosphere has undergone significant deformation in the southwestern Ordos Block under the influence of the Tibetan Plateau.The influence of the plateau expansion on the Ordos Block is obviously beyond the Liupanshan thrust belt.The high-velocity anomaly shrinks to the central and southeastern regions in this block at the long periods(80～100 s),and the anisotropy is significantly stronger around the high-velocity region,which reveals that the boundary zones of Ordos Block have been subjected to different degrees of deformation and modification,and resulting in non-uniform lithospheric thinning.Datong volcanic field in the north of Shanxi Rift Zone is characterized by low velocity anomaly at periods of greater than 20 s,and the anisotropy shows significant difference at different periods.We speculate that this phenomenon is related to the geometry of lithosphere at different depths in the northeastern Ordos Block and the long-range compression effect from Tibetan Plateau.High-velocity and near E-W fast wave direction are shown at periods of 20～60 s in central and southern Shanxi Rift Zone,which consistent with that in the central and eastern Ordos Block.We speculate that the lithosphere still remains some properties of the ancient North China Craton in this region.In northeastern margin of the Tibetan Plateau,where dominated by prominent low-velocity anomaly and consistent NWW-SEE fast wave direction at different periods,indicating consistent deformation of the crust,upper mantle lithosphere and asthenosphere beneath this region,which supports the vertical coherent deformation model.
Ordos BlockShanxi Rift ZoneNortheastern margin of Tibetan PlateauEikonal surface wave tomographyPhase velocityFast wave direction
万方数据
维普
