青藏高原东北缘SKS波分裂研究
SKS Wave Splitting of the Northeastern Margin of the Qinghai Tibet Plateau

利用青藏高原东北缘区域数字地震台网43个台站的远震SKS波形资料，采用最小能量法和旋转相关法得到台站下方上地幔介质各向异性的分裂参数：快波偏振方向（φ）和快慢波时间延迟（δt）。研究结果表明：在塔里木盆地东南缘区域，各向异性快波方向与该区域的断裂走向存在明显的夹角，该盆地向柴达木盆地的俯冲方向一致，各向异性归因为古构造运动遗留下的“化石各向异性”，且由于壳幔物质的拆沉作用，推测该区域壳幔之间存在解耦作用；在祁连-河西走廊区，SKS快波偏振方向呈NW-SE，与主要断裂带的走向一致；在西秦岭北缘断裂带附近，观测到快慢波时间延迟有着较大的变化，可能是岩石圈变形和软流圈物质流动共同导致；在鄂尔多斯板块内，快波方向呈NW-SE方向，可能暗示青藏高原深部物质分叉绕流运动。青藏高原东北缘不同区域台站下方的各向异性均具有差异性，进一步证实了青藏高原东北缘地区构造变形的复杂性。
Based on the teleseismic SKS phase recorded by 43 permanent broadband stations in Gansu Province in the northeastern margin of the Qinghai-Tibetan plateau, this study obtains the splitting parameters of the fast-wave polarization direction and delay times at each station using the minimum energy and rotation-correlation methods. The results can be summarized as follows. In the southeastern region of Tarim Basin, the fast-wave polarization sites exists obvious angle with the strike of regional faults, and coincides with the subduction direction from Tarim Basin to Qaidam Basin. This result reveals that the upper mantle deformation is mainly affected by ancient tectonic movement. The anisotropy observed may be considered "fossil" anisotropy. Because of crust-mantle delamination, decoupling between the crust and mantle occurs in this area. In the Qilian-Hexi Corridor region, fast-wave polarization shows a NW-SE trend, consistent with the strike direction of the main faults in this region. Comparison of the fast-wave direction with the direction of lithospheric extension and GPS-observed velocity reveal that the deformation model of the crust and upper mantle may be vertically coherent deformation. In the northern fringe fault of the western segment of the Qinling mountains, slow-wave time delays exert significant anisotropy in the vicinity. This phenomenon could indicate upper mantle deformation, which is caused by both deformation of the lithosphere and flow of the asthenosphere. In the Ordos block, the fast-wave direction shows a NW-SE trend, which suggests that the movement of deep material exists motion of flow around the Tibetan plateau. Collision between plates causes thickening and uplifting of the western China crust and eastward extrusion of material in the northeastern margin of the Qinghai-Tibetan plateau. Different regional stations present different levels of anisotropy in the northeastern margin of the Qinghai-Tibetan plateau, which further proves the complexity of tectonic deformation in its northeastern margin. According to the splitting parameters of SKS waves, the anisotropic characteristics of the study region are analyzed to investigate dynamic