阿尔金断裂中段南月牙山古地震地表破裂带及其构造意义  

THE PALEOSEISMIC SURFACE RUPTURE AT SOUTH OF CENTRAL ALTYN TAGH FAULT AND ITS TECTONIC IMPLICATION

作　　者：邵延秀[1] 袁道阳 刘静 Jerome Van der Woerd 李志刚 吴磊[6] 刘方斌[7] SHAO Yan-xiu;YUAN Dao-yang;LIU-ZENG Jing;Jerome Van der Woerd;LI Zhi-gang;WU Lei;LIU Fang-bin(Lanzhou Institute of Seismology,CEA,Lanzhou 730000,China;School of Earth Science,Lanzhou University,Lanzhou 730000,China;Institute of Surface-Earth System Science,Tianjin University,Tianjin 300072,China;Institut de Physique du Globe de Strasbourg EOST,5 rue Ren Descartes,Strasbourg Cedex 67084,France;School of Earth Science and Engineering,Sun Yat-sen University,Guangzhou 510275,China;School of Earth Sciences,Zhejiang University,Hangzhou 310027,China;Shandong Earthquake Agency,Jinan 250014,China)

机构地区：[1]中国地震局兰州地震研究所,兰州730000 [2]兰州大学地质科学与矿产资源学院,兰州730000 [3]天津大学表层地球系统科学研究院,天津300072 [4]法国斯特拉斯堡地球物理研究所,法国斯特拉斯堡67084 [5]中山大学地球科学与工程学院,广州510275 [6]浙江大学地球科学系,杭州310027 [7]山东省地震局,济南250014

出　　处：《地震地质》2020年第2期435-454,共20页Seismology and Geology

基　　金：中国地震局地震预测研究所基本科研业务专项(2018IESLZ01);中国地震局地震科技星火计划项目(XH19044,XH18048);国家自然科学基金(41802228,U1839203)共同资助。

摘　　要：阿尔金断裂是青藏高原东北缘的一条重要的边界断裂,其几何结构和运动学性质对青藏高原的构造演化具有重要的指示意义。通过卫星影像解译和野外实地调查,在柴达木盆地西缘、索尔库里盆地南约10km的盐壳区发现一长约14km的古地震地表破裂带。该地震破裂带与阿尔金主走滑断裂近平行,根据几何形态大致可将其分为3段走向不同的次级段落,总体走向为N80°E,但局部段落的走向存在变化。该破裂带的构造样式以挤压隆起、次级断裂、裂槽、三角拉分盆地和断陷盆地为主要特征,多相间出现,是典型的走滑断层上的地震破裂带特征,文中利用野外活动断裂地质填图方法标绘了30余个挤压隆起体。另外,考察中还发现在多数挤压隆起上有多次地震重复活动的证据。根据附近盐壳钻孔年龄和地震裂缝中沉积物的年龄结果推测,最新一次地震事件发震时间的下限为全新世。该地震地表破裂带向E进入大通沟南山,其地貌特征表现为较连续的逆冲陡坎,而向W破裂带逐渐消失。通过地震反射剖面推测认为该破裂带向W与阿尔金断裂平顶山次级断裂相接。作为阿尔金断裂的1个构造节点,平顶山将部分应变传递到青藏高原内部的月牙山-大通沟断裂,其多次活动造成了月牙山东约14km长的地表破裂带。In this study,we described a 14km-long paleoearthquakes surface rupture across the salt flats of western Qaidam Basin,10km south of the Xorkol segment of the central Altyn Tagh Fault,with satellite images interpretation and field investigation methods.The surface rupture strikes on average about N80°E sub-parallel to the main Altyn Tagh Fault,but is composed of several stepping segments with markedly different strike ranging from 68°N^87°E.The surface rupture is marked by pressure ridges,sub-fault strands,tension-gashes,pull-apart and faulted basins,likely caused by left-lateral strike-slip faulting.More than 30 pressure ridges can be distinguished with various rectangular,elliptical or elongated shapes.Most long axis of the ridges are oblique(90°N^140°E)to,but a few are nearly parallel to the surface rupture strike.The ridge sizes vary also,with heights from 1 to 15m,widths from several to 60m,and lengths from 10 to 100m.The overall size of these pressure ridges is similar to those found along the Altyn Tagh Fault,for instance,south of Pingding Shan or across Xorkol.Right-stepping 0.5~1m-deep gashes or sub-faults,with lengths from a few meters to several hundred meters,are distributed obliquely between ridges at an angle reaching 30°.The sub-faults are characterized with SE or NW facing 0.5~1m-high scarps.Several pull-apart and faulted basins are bounded by faults along the eastern part of the surface rupture.One large pull-apart basins are 6~7m deep and 400m wide.A faulted basin,80m wide,500m long and 3m deep,is bounded by 2 left-stepping left-lateral faults and 4 right-stepping normal faults.Two to three m-wide gashes are often seen on pressure ridges,and some ridges are left-laterally faulted and cut into several parts,probably owing to the occurrence of repetitive earthquakes.The OSL dating indicates that the most recent rupture might occur during Holocene.Southwestwards the rupture trace disappears a few hundred meters north of a south dipping thrust scarp bounding uplifted and folded Plio-Quaternary

关 键 词：阿尔金断裂 柴达木盆地 古地震地表破裂带 走滑断裂 

分 类 号：P315.2[天文地球—地震学]