西藏许如错地区中全新世地震触发软沉积物变形构造及其地质意义  

Earthquake-Induced Soft-Sediment Deformation Structures in Middle Holocene of Xuru Co Area in Tibet and Its Geological Significance

作　　者：秦雅东[1] 张士贞 刘函[1] 李勇[1] Qin Yadong;Zhang Shizhen;Liu Han;Li Yong(Chengdu Center of China Geological Survey,Chengdu 610081,China)

机构地区：[1]中国地质调查局成都地质调查中心,四川成都610081

出　　处：《地球科学》2020年第8期2945-2956,共12页Earth Science

基　　金：中国地质调查局项目(Nos.DD20160015-31,DD20190053)。

摘　　要：湖相沉积古地震研究是对地表破裂古地震研究的重要补充.通过详细的野外地质调查,在西藏许如错地区全新统湖相地层内新发现大量地震触发软沉积物变形构造(震积岩),层内发育液化脉、液化曲卷变形、液化角砾岩、液化水压构造、滴状体与锥状体、砾石丘、负载构造和火焰构造等软沉积变形标志,还发育同震断层、震裂缝和同震褶皱等同震构造标志.根据软沉积变形标志与震级之间的关系,结合历史地震统计液化颗粒范围,通过C14和光释光年龄测定,推测古地震事件发生在±7.5 ka,MS>7.5级;填补了该区历史地震的空缺,为恢复青藏高原南北向地堑地震活动历史及迁移规律提供了素材.震积岩中见大量砾石液化现象,这对现阶段以砂土-粉砂土研究为主的砂土液化调查工作提出了新挑战.The lacustrine paleo-seismic study is an important supplement to the research of a complete paleo-seismic sequence.A large number of earthquake-induced soft-sediment deformation structures(seismites)were newly discovered in the Holocene lacustrine deposits in Xuru Co area by detailed field geological survey.Soft-sediment deformation markers mainly include liquefied vein,liquefied convolute,liquefied breccia,hydraulic structure,liqufied droplets and cusps,conglomerate mound,load structure and flance structure.The syn-seismic structure deformation markers were also developed including syn-seismic fault,seismic fissure,and syn-fold.Based on the empirical statistical relation between the earthquake magnitude and soft-sediment deformation markers,combining historical earthquake statistics with the range of liquefied particles,it is suggested that the maximum magnitude may exceed 7.5.The C14 and OSL dating results for samples suggest that the age of the paleoearthquake is around 7.5 ka.The work fills the gap of historical earthquakes in the area,and provides material for restoring the history and migration law of earthquakes in the NS-trending grabens of the Tibetan Plateau.A large amount of gravel liquefaction was found in seismite,which poses a new challenge to the investigation of sand liquefaction,which is dominated by sand and silt.

关 键 词：震积岩 古地震 全新统 砾石液化 许如错地堑 地层学 

分 类 号：P539.6[天文地球—古生物学与地层学]