乌鲁木齐地区N倾断层系的构造特征

THE STRUCTURAL CHARACTERISTICS OF THE N-DIPPING FAULT SYSTEM IN URUMQI AREA

乌鲁木齐地区发育有5条N倾的断层，这些断层晚更新世以来均有较为明显的活动迹象，并在地表形成了较为显著的构造标志。通过沿断层大比例尺地质地貌填图、探槽开挖和年代测定，较为准确地获得了断层的最新活动时代、运动性质和特征等问题，并确定出这些断层都是在距今20万年-30万年以来快速翘升形成的。结合深地震反射资料，对乌鲁木齐地区的深部结构进行了分析讨论，从而对N倾断层系的深部构造特征也有了更加清晰的认识，为准确评价这些断层的孕震模式和发震能力提供了可靠的依据。

Urumqi lies at the transform site between the range-front fault-fold system of the North Tianshan and Bogeda nappe structural system. The neotectonics is very strong in this area. There are five N-dipping faults in the Urumqi area which formed on the basis of upwarping range-front fluvial and ice-water deposit platforms of the middle Pleistocene. The TL dating of the samples show that the age of this set gravel platforms is about 200 - 300 ka. Thus, it can be estimated that the N-dipping fault system was generated by rapid upwarping since the time 200 -300 ka B. P. The N-dipping fault system dislocated the gravel platform of the middle or late Pleistocene, generating apparent fault scarps on the surface. The Xishan fault, the Wangjiagou fault set and the Jiujiawan fault set which lie in the west of Urumqi are all frontal faults of the northern Tianshan nappe structural system. They are of recoil faults which are generated by tilting of the Xishan block. The relatively independent structure system converges at the decollement which is located about 10 km below the surface. The kinetic intensity of the Xishan fault is gradually subdued from west to east. The Wanyaogou fault and the Baiyangnangou fault which lie in the east of Urumqi are all branch faults of the Bogeda nappe structural system. They are all recoil fault which are generated from upper fault fah. The Wanyaogou fault converges at the decollement about 5 km below the surface. The Baiyangnangou fault converges at the decollement about 6 km below the surface. The kinetic intensity of the two faults is gradually subdued from east to west.