Abstract: By analyzing the seismicity in Kuqa depression,north Tarim Basin,some active basement faults are inferred from the distribution of earthquake epicenters in several profiles.The different deformation characteristics between the cover and the basement,as well as their reasons are investigated by comparing the locations of surface structures and basement faults,combined with some other results of deformation and kinematic research in this region.The following conclusions can be drawn from the present study: (1)The distribution of earthquake epicenters indicates that active basement faults exist along the tectonic grain corresponding to that of the surface structures of the Qiulitage-Yaken tectonic belt in Kuqa depression.In the basement beneath the East and West Qiulitage anticlines,there exist the East,North and South Qiulitage deep faults.Moreover,in the basement beneath the Yiqikelike anticline and Yaken anticline there exist the Yiqikelike and Yaken deep faults.These facts may imply that the development of surface structures was controlled by the deep structures. (2)It is revealed that a NE-trending deep strike slip fault is developed along the line from the west end of the Yiqikelike anticline to the Dongqiu No.5 well,and a NW-trending deep fault is developed on the west side of Baicheng.These two active deep faults cut the tectonic grain of the region,and might be responsible for the segmentation of tectonics in Kuqa depression,probably has led to the greater contraction at the middle segment of Kuqa depression(Kuqa-Baicheng)and smaller contraction at east and west segments.(3)The different characteristics of media result in the different deformation between the cover and the basement.The strength of the lithosphere at the basement of Kuqa depression is extremely high,so that deformation of the basement here is dominated by brittle fracturing and the generation of earthquake.The strength of the sedimentary rocks in the cover is much weaker,which may cause the plastic flow of the rocks under the action of long-period intense compression from the orogenic belt.And especially with the existence of coal or salt layers of extremely weak strength in the cover,a large scale aseismic detachment may occur along these weak layers.

Key words: seismicity, surface structure, basement fault, deformation characteristic, Kuqa depression

摘要： 通过研究库车地区的地震活动性,由地震分布的规律性推断可能的基底断裂,并分析了基底活动断裂与地表构造的对应关系、盖层变形和基底变形特征的差异及成因。结果表明:1)地震震中分布揭示库车坳陷内对应东、西秋里塔格背斜带位置上,基底中发育东秋里塔格深断裂和南、北秋里塔格深断裂;另外,依奇克里克背斜和亚肯背斜位置上也存在对应的深断裂,这表明地表构造的形成受深部构造的控制。2)依奇克里克构造西端至东秋 5井连线位置上发育1条NE向走滑断裂,在拜城西侧发 1条NW走向的活动断裂,这2条切穿构造走向的活动断裂是库车坳陷构造分段的主因。3)基底和盖层变形特征的差异主要源于二者之间介质特性的差异。盆地基底岩石圈强度非常高,决定了其变形以脆性破裂———地震活动为主;而盖层中沉积岩层强度较弱,且存在煤和膏盐等极软弱的薄层,在构造挤压作用下,可以产生黏性或塑性流动大变形及顺层无震滑脱。

关键词: 地震活动性, 地表构造, 基底断裂, 变形特征, 库车坳陷