It has been generally accepted that the geo-morphological features and the basic tectonic framework of the northeastern margin of Qinghai-Tibetan Plateau are controlled by the Altun sinistral strike-slip fault,the East Kunlun sinistral strike-slip fault and Haiyuan sinistral strike-slip fault.Theoretically,the earthquakes should have been very popular accompanying the subduction,the collision and the orogenic processes of these faults.In 2011 and 2012,the authors have conducted the geological survey and study on the seismic event deposits along the northeastern margin of the plateau and found a number of soft-sediment deformation structures and some other syndepositional faults which could be explained as seismites in the successions from the Upper Triassic to the Quaternary,with the only exception of Jurassic.The main types of seismites include convolute bedding in the Upper Triassic at Baojishan;the load,ball-pillow features in the Lower Cretaceous at Mitan village; the liquefied diapers in the Lower Cretaceous at Changma village; the liquefied veins,slumps and the micro intra-strata faults in the Quaternary at Chijinpu village and Ciyaokou village.All of these seismites are spatially located in the vicinity of the major fault.The time and space distribution of these seismites can be used to rebuild the regional long-term seismicity and to recover the activity history of major faults.Based on the findings of large amount of liquefied seismites in the Upper Triassic near Haiyuan fault,the authors propose that the initial activity time of Haiyuan fault is probably from Late Triassic.%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.
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