Crustal S-velocity and radial anisotropic structure of the Ordos Block and its adjacent areas from full-waveform tomography
The Ordos Block and its adjacent areas are not only the hot spots for studying the interaction between active blocks,but also the migration of materials between active blocks.However,the coupling relationship between the crustal deformation in and around the Ordos Block and the extension of the Tibetan Plateau remains to be determined.In this paper,based on the seismic data in the 20～40 s recorded by permanent stations from China National Seismic Network and mobile stations from ChinArray-Himalaya broadband seismic array,the three-dimensional S-wave velocity structure and radial anisotropy structure in the study area are obtained by using full-waveform tomography.The imaging results revealed that:There is a difference in velocity structure between the north and south part with 37° N as the boundary.The low-velocity feature of the southern Ordos reflects the thicker crust,which corresponds to the topography.The middle and upper crust in the southwest margins show negative radial anisotropy,in which the S-wave velocity perturbation in the middle crust is a significant low-velocity anomaly,extending to the southwest of the Ordos Block.This region is speculated to be the front edge of the expansion of the Tibetan Plateau.It is believed that the velocity structure characteristics reflect the crustal shortening model that detachment in the middle crust and thickening deformation in the upper crust underneath the southwest margins of the Ordos Block.The southern Alashan Block,which has the characteristics of early tectonic deformation during the expansion of the Tibetan Plateau,shows relatively low-velocity feature and obvious negative radial anisotropy in the upper crust.There is a difference in velocity structure between the north and south part of the Shanxi rift zone in the eastern margin of Ordos.The lower crust of the northern Shanxi rift zone shows low-velocity anomaly,reflecting the accumulation of weak materials under the influence of mantle thermal material transformation,while the central Shanxi rift zone is a relatively high-velocity structure,suggesting that the deep tectonic stress and strain environment is stable.In addition,the negative radial anisotropic structures are distributed in the northern section of The North-South Seismic Belt(NSSB)and the upper crust of the Shanxi rift zone,which provides waveform imaging evidence for further study of the relationship between seismicity and crustal velocity structure.
The Ordos BlockFull-waveform tomographyRadial anisotropy3-D crustal velocity structure
万方数据
维普
