【摘要】 青藏高原东北缘的地质地貌特征与基本构造格架受阿尔金左行走滑断裂、东昆仑左行走滑断裂和海源左行走滑断裂控制,在青藏高原的碰撞造山过程中地震作用贯穿始终。2011至2012年,作者对青藏高原东北缘东起靖远(海原断裂东段)西至昌马盆地(阿尔金断裂东南)的软沉积物变形(震积岩)进行的系统调研表明,青藏高原东北缘祁连山地区从三叠纪至第四纪各时代(侏罗纪以外)的地层中,均发现丰富的古地震纪录(震积岩)。代表性震积岩发现点和层位有:靖远宝积山上三叠统、靖远糜滩乡下白垩统、昌马盆地下白垩统以及赤金堡和酒泉磁窑口附近的第四系。主要的震积岩类型有:液化脉、负载、球-枕构造、液化卷曲、层间微断裂等。根据区域地质资料分析,这些震积岩均分布于区域性大断裂附近。本文简单讨论了主要震积岩发现点与其相邻的区域构造(地震)活动之间的关系,根据靖远附近上三叠统普遍发育震积岩,提出海原断裂带的初始活动时间很可能就在晚三叠世,与青藏高原东缘龙门山地区印支期的造山地震同时期。更多还原

【Abstract】 Marking the northern margin of the Tibet Plateau,the Altyn Tagh fault system not only truncates various geological units, controlling both the geometric characters and tectonic framework in northern Tibet,but also comprises the main passage where the landmass easternward extrude. It is crucial to study the fault system’s forming,active ages and fault trace evolvement to probe the dynamic mechanism of the Tibet Plateau. Here,we take advantage of the soft sediment deformation revealed in Middle Jurassic lacustrine strata in southern Subei to explore such questions. There are generally 26 deformation layers found which can be further subdivided into 4 categories in the field: load and pillow structure,liquefied diapir and crater,liquefied breccia and convoluted structure. The grain size statistic shows the grains mainly range from 0.2～0.3mm ( 60% ) ,highly comparable with the modern earthquake ejected and experimental grains size,thuswe consider them as earthquake induced liquefaction. Based on the empirical statistical relation between the earthquake magnitude and the maximum liquefactiondistance,we presume the minimum magnitude is 6～6. 5,whereas,in view of the specific deformation structure with different magnitude,we suggest the maximum magnitude may exceed 7. 5. The 26 deformation layers represent an earthquake episode in Middle Jurassic,with at least4 earthquakes. The Altyn Tagh fault system was highly active in Middle Jurassic and the fault trace had already reached Subei area at least. Given the Triassic active agededuced from the mylonite in Xorkol and the volcano activities in Cretaceous and Jurassic,soft sediment deformation in Yumen area in Cretaceous,the Altyn Tagh fault may have experienced at least three active ages: the Late Triassic,the Middle Jurassic and the Cenozoic,with the fault length expand from several hundred kilometers to more than 1000 kilometers and to 2000 kilometers.更多还原