阿尔金北缘断裂带东北段第四纪构造活动与地震

本文概述了阿尔金北缘断裂带东北段(甘肃境内)的地质背景和新构造运动,讨论了断层特性、断层几何学、形变图象及一些特殊走滑运动地貌等问题。根据第四纪后期不同时代的地貌单元被水平左旋错移的幅度,结合C~(14)年代测定,求出5个不同时代至今的平均滑动速率,并分析了断层活动的一些时空特点。文章还探讨了古地震现象,现代地震活动与断裂的关系及地震危险性,较详细地研究了新发现的芦草沟古地震形变带。

THE QUATERNARY STRUCTURAL ACTIVITIES AND SEISMICITY ON THE NORTHEASTERN SECTOR OF THE NORTH FRINGE FAULT ZONE OF AERJIN MOUNTAINS

The north fringe fault zone of Aerjin mountains is an important fault in Aerjin fault system (Altyn Tagh fault system).It might have existed in Late Proterozoic and became the boundary fault between Talimu Plateform and paleo-ocean plate in Paleozoic.In the neotectonic movement it has had very intense activities particularly left-lateral strike-slip movement.In this paper its notheastern sector is studied.On this sector of the fault zone a thick fault gouge belt and a wide cataclastic rock belt were observed.The plane distribution of the fault zone often exhibits an echlon or oblique connexion pattern.The deformation and some specific geomorphic features caused by strike-slip movement of fault are given.According to a great deal of data of the displacement distance on water system and other geomorphic unit we obtained four average slip rates from diffirent times in late Quaternary to today.They are 5.8mm/yr.from Middle Pleistocene,3.4-4.0mm/yr.from the lntersadial of middle Pleistocene,4.0-4.5mm/yr.from Late Pleistocene,and 8.0mm/yr.from Holocene.Based on C¹⁴ dating,the rate is more than 3.6mm/yr.from late Holocene.In the northeastern sector we found some paleoseismic traces and afresh paleoearthquake deformation belt in Lucaogo,where we estimatedthat the earthquake occurred about 300 years ago and M=7.0-7.5 according to the slope of fault scarps and length of fracture belt.The relationship between recent seismicity and the fault zone,the seismic risk and great earthquake recurrence are discussed.