SUMMARY The Ordos Block is located at the intersection of the Tibetan Plateau, the South China Plate and the North China Craton. The deep deformation of its surrounding areas is geologically complicated. Seismic anisotropy provides information about past and present deformation of the upper mantle and helps to better understand deep deformation processes. We obtained the anisotropic pattern at high resolution within and surrounding the Ordos Block by analysing teleseismic data from ∼710 newly deployed temporary seismic stations based on SKS phases from ∼86 earthquakes. The central and eastern Ordos Block with a relatively thick and rigid lithosphere is characterized by a weak anisotropy. In the western part of the Ordos Block, the fast-wave polarization direction is dominantly NW–SE. We believe the lithosphere in the western part of the Ordos Block may have undergone significant deformation caused by expansion and compression of the Tibetan Plateau. Near the Datong Basin, the delay time is 0.92 s and the fast-wave polarization direction is mainly oriented NW–SE, perpendicular to the NE-directed compression of the Tibetan Plateau and parallel to the basin extension direction. We speculate that this anisotropy is related to the long-range effect of NE compression of the northeastern Tibetan Plateau on the low-velocity upper mantle in this area. The weak anisotropy in the central part of the Shanxi Rift indicates that the thickness and mechanical strength of the high-velocity lithosphere are higher than in the southern and northern regions.

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鄂尔多斯地块及周边地区地震各向异性及其对岩石圈变形的影响

摘要 鄂尔多斯地块位于青藏高原、华南板块和华北克拉通的交汇处。其周边地区的深层变形地质复杂。地震各向异性提供了关于上地幔过去和现在变形的信息，有助于更好地理解深部变形过程。我们通过分析来自~710 个新部署的临时地震台站的远震数据，基于~86 次地震的SKS 阶段，获得了鄂尔多斯地块内部和周围的高分辨率各向异性模式。鄂尔多斯地块中东部岩石圈较厚、较坚硬，各向异性较弱。鄂尔多斯地块西部的快波偏振方向以NW-SE为主。我们认为鄂尔多斯地块西部的岩石圈可能由于青藏高原的膨胀和压缩而发生了明显的变形。在大同盆地附近，延迟时间为0.92 s，快波极化方向主要为NW-SE，垂直于青藏高原NE向压缩，平行于盆地伸展方向。我们推测这种各向异性与青藏高原东北部的NE压缩对该地区低速上地幔的远距离影响有关。山西裂谷中部的弱各向异性表明高速岩石圈的厚度和机械强度高于南北地区。