秋里塔格褶皱带东段探槽的古地震事件  

STUDY ON PALEO-SEISMIC EVENTS IN TRENCHES OF THE EASTERN QIULITAGE ANTICLINAL BELT

作　　者：张玲[1] 杨晓平[1] 李胜强[1,2] 黄伟亮 杨海波[1] ZHANG Ling;YANG Xiao-ping;LI Sheng-qiang;HUANG Wei-liang;YANG Hai-bo(State Key Laboratory of Earthquake Dynamics,Institute of Geology,China Earthquake Administration,Beijing 100029,China;Hebei Earthquake Agency,Shijiazhuang 050021,China;Key Laboratory of Western China Mineral Resources and Geological Engineering,College of Engineering and Surveying of Chang′an University,Xi′an 710064,China)

机构地区：[1]中国地震局地质研究所,地震动力学国家重点实验室,北京100029 [2]河北省地震局,石家庄050021 [3]长安大学,西部矿产资源与地质工程教育部重点实验室,西安710064

出　　处：《地震地质》2020年第5期1039-1057,共19页Seismology and Geology

基　　金：全国重点监视防御区活动断层地震危险性评价项目(1521044025);区划图预研“逆冲型构造区潜在震源划分原则与三维模型构建方法”和西北潜在震源调整研究共同资助。

摘　　要：位于天山南麓库车坳陷中的东秋里塔格背斜带是典型的活动逆断裂褶皱带,1949年的库车M 71/4地震发生在该逆断裂褶皱带上。目前,仍然没有发现此次大地震的地表破裂带,也没有确定其发震断层。同时,由于这一地区相关的年代学研究匮乏,对于这一地区的古地震事件仍然缺乏系统性地认识。文中基于野外调查获取的地表地质特征和通过石油地震反射剖面解读的深部构造,定性地分析了研究区内的地表活动断层与深部低倾角滑脱断层、褶皱变形的关系。我们聚焦于冲破至地表的活动断层,选择在库车塔吾背斜北翼和东秋里塔格背斜南翼的突破断层上开挖了5个探槽,分析了探槽中与古地震事件相关的构造和地层沉积特征。根据OSL(光释光)和14 C测年结果,利用逐次限定法识别出了6次古地震事件。在这些古地震事件中,有的地表破裂同时发生在褶皱带南、北两翼的突破断层上,有的仅在褶皱带北翼的突破断层上发生。总体而言,这些古地震事件引起的地表破裂具有南天山低角度逆断层古地震破裂变形普遍存在的2种现象,即单条断层多次破裂和多条断层同时破裂。已揭示的古地震事件具有一定的丛集性,在距今7.4ka以来具体表现为:距今5.7~7.4ka共发生了3次古地震事件,在距今3.3~4.7ka发生了1次古地震事件,最新的丛集事件可能以1949年库车M 71/4地震的发生为标志。研究区地震丛集的发生近似有2.5~4ka的重复周期,1949年库车M 71/4地震之后是否还会发生强震,还有待进一步的观察和详细研究。In response to the ongoing far-field effects of the India-Eurasia collision,the Tianshan Mountains experience rapid NS convergence,and most of the present N-S shortening is absorbed along the southern and northern edges.The resultant frequent large earthquakes have inspired many scientists to explore the neotectonic activity of the Tianshan Mountains.The eastern Qiulitage anticlinal belt located in the Kuqa depression,on the southern piedmont of the Tianshan Mountains,is a typical blind fault-related fold.The Kuqa M 71/4 earthquake in 1949 as typical folding earthquake once occurred on the northern limb of the eastern segment of the Qiulitage anticline,and the epicenter was near the Village of Kang which is sparsely populated.This earthquake is a typical folding earthquake whose dominant fault did not thrust onto the earth surface.Although many tectonic-induced scarps and deformed Quaternary strata have been reported,there are still no direct evidences for the surface ruptures and corresponding causative faults of this earthquake at present.And systematic understanding of paleoseismic events in Qiulitage area is also limited by the lack of relevant chronological researches.We conducted 1︰50-000 scale geological mapping in the Qiulitage anticline area.The local surface geological characteristics are investigated based on interpretation of Google Earth image and confirmation in the field.Together with interpreted subsurface structure by petroleum seismic reflection profiles,the relationship between the active faults thrust on the surface,low-dip-angle decollement faults in deep,and fold deformation are subsequently qualitatively analyzed.In this study,the active faults which have thrust to the surface and generated fault scarps are focused on.Totally five trenches were chosen and cleared up,two of which are located on the southern limb of the eastern Qiulitage anticline and the others are on its northern limb.And all excavation sites are situated on fresh fault scarps.We carefully interpreted different characteri

关 键 词：古地震 秋里塔格背斜带 逆断裂褶皱带 库车地震 天山 

分 类 号：P315.2[天文地球—地震学]