天山地区跨断层形变观测与地壳应力特征

Cross-fault deformation observation and characteristics of crustal stress in Tianshan region

采用“将断层两盘作为不变形的刚体来分析断面相对滑动与地表两盘点位相对位移的定量关系”的方法，对天山地区6个跨断层测点的形变观测资料进行处理，获得断层滑动的位移数据；利用滑动拟合法进行反演计算，从而获得天山地区6个测点处地壳应力状态的基本特征，从而分析天山地区地壳应力的应力方向、应力结构等基本特征，探索天山地区所处的地壳应力环境。研究表明，天山地区6个测点处地壳应力状态的基本特征为：北天山呼图壁测点的应力结构为走滑型，表现为NNW-SSE向的挤压和NEE-SWW向的拉张；石河子的应力结构为逆断型，表现为NNW—SSE向的挤压；独山子测点的应力结构为逆走滑型，表现为NNE—SSW向的挤压和NNW-SSE的拉张。南天山库尔勒、阿克苏与克孜尔3个测点的应力结构均为走滑型，其中库尔勒表现为NNW—SSE向的挤压和NEE—SWW的拉张，阿克苏为NWW—SEE向的挤压和NEE—SWW向的拉张，克尔孜则表现为NWW-SEE向的挤压和NNE-SSW向的拉张。利用跨断层资料反演得到的6个测点的应力状态与由断层滑动资料及震源机制解数据反演得到的构造应力场方向存在10°～20°的偏差，其原因是不同深度的应力资料反映了不同的应力方向。另外，印度板块与欧亚大陆的碰撞使得天山地区的区域构造应力场表现为近南北向的挤压。处于南北向同一构造应力作用下的6个测点，由于其测点位置处于不同走向的活动断裂上，因此表现出各不相同的应力状态。

To study the characteristics of crustal stress, including the stress direction and the stress regime, to explore the crustal dynamic environment in Tienshan region. Based on the deformation observation data of 6 crossfault survey point in Tienshan region, taking the two walls of fault as indeformable rigid block and analyzing the quantitative relationship between relative sliding of fault planes and relative displacement of the sites on the two walls on the ground surface to obtain the fault slip data, and then using the Sliding Direction Fitting Method （SD- FM） to invert the basic characteristics of crustal stress of 6 cross-fault survey points in Tienshan region. The inverted result from cross-fault data of 6 survey points indicates that the stress regime is strike-slip type at Hutubi point in the north Tienshan and its crustal stress is characterized by NNW-SSE compressional stress and NEE-SWW extensional stress. At Shihezi point, the stress regime is reverse-slip type and the crustal stress is in NNW-SSE compressional stress direction. And at Dushanzi point, the stress regime is dominated by reverse-slip type, with some strike-slip components and the crustal stress is characterized by NNE-SSW compressional stress and NNW-SSE extensional stress. However, the stress regime of 3 survey points in the south Tienshan are all strike-slip type, and they show different characteristics of stress direction. At Kuerle point, the crustal stress is in NNW-SSE compressional and NEE-SWW extensional direction. At Akesu point, the crustal stress is characterized by NWW-SEE compressional stress and NEE-SWW extensional stress. And at Keerzi point, the crustal stress is in NWW-SEE com- pressional and NNE-SSW extensional direction. The direction of crustal stress inverted from cross-fault data of 6 survey points has a small deviation angle of 10° -20° compared to the results inverted from fault slip data and focal mechanism solutions. The possible reason is that different stress data in different depth reflect the different stress direction. In addition, the regional stress field in Tienshan area is now characterized by North-South compressional stress, which was caused by the collision of the Indian Plate and the Eurasian Plate. And the 6 cross-fauh survey points are located on the faults with different striking, so they show different stress state. This result not only has important scientific significance to the seismic hazard prediction, it also has great practical value to the site planning and construction for all kinds of major projects.