中天山及邻区S波分裂研究及其动力学意义

本文利用天山及其邻区布设的37个宽频带地震台站记录到的远震波形数据，分别采用最小能量法和旋转相关法对SKS和SKKS波震相进行了偏振分析，计算出了台站下方介质的S波分裂参数：快波的偏振方向（φ）和慢波延迟时间（δt）.本文研究结果表明：中天山内部大多数台站的各向异性快波方向呈NEE-SWW向，与天山走向平行，慢波时间延迟为0.4～1.7 s，这是塔里木、哈萨克斯坦的南北双向俯冲及其导致的天山地区岩石圈地幔南北向缩短变形的直接反映.本文研究发现中天山北部部分台站下方地震各向异性快波方向与慢波延时随方位角呈现规律性的变化，可能暗示该区上地幔各向异性不能仅用单层水平各向异性这一简单模式来解释.75°E以西的天山地区台站下方S波快波方向和延时具有强烈的横向变化，可能与研究区下方存在的小规模对流有关.中天山不同地段地震台站下方各向异性明显不同，进一步证实了天山地区构造变形的复杂性.

The shear wave splitting of Central Tien Shan and its implications

Seismic anisotropy beneath the Central Tien Shan is investigated using shear-wave splitting of SKS and SKKS phases. We analyzed teleseismic events recorded by 37 broadband stations in the Central Tien Shan and its vicinity. Fast polarization directions (φ) and delay times (δt) are determined with both the minimum energy method and rotation-correlation method. Our results suggest that the fast polarization direction of most stations in this area is NEE-SWW, parallel to the strike of the Tien Shan, the delay time is about 0.4~1.7 s. All of these are exactly the direct reflection of the NS shortening deformation of the lithosphere mantle beneath this area, which is related to the double subduction of Tarim and Kazakhstan. At some stations in the northern part of Central Tien Shan the splitting parameters vary with event back azimuth regularly, which implies that the actual upper-mantle structure is more complex than a single anisotropic layer with horizontal fast axis. The strong transverse variety of the shear wave fast polarizations and delay times of the stations in the west of 75°E maybe related to the small-scale convection beneath this region. The obvious differences of anisotropy between different parts of the Tien Shan verify the complexity of the lithosphere deformation beneath this region.