基于河流裂点序列研究秦岭北缘断裂强震活动历史  

Evaluating knickpoint retreat along the Qinling north piedmont fault for paleoseismological analysis during Holocene

作　　者：黄伟亮 杨虔灏 彭建兵[1] 项闻 原浩东 王淞 HUANG Weiliang;YANG Qianhao;PENG Jianbing;XIANG Wen;YUAN Haodong;WANG Song(College of Geological Engineering and Surveying of Chang'an University/Key Laboratory of Western China Mineral Resources and Geological Engineering,Xi'an 710054,Shaaxi;Nuclear Industry Jinhua Exploration Design Institute Co.,Ltd.,Jinhua 321000,Zhejiang)

机构地区：[1]长安大学地质工程与测绘学院,西部矿产资源与地质工程教育部重点实验室,陕西西安710054 [2]核工业金华勘测设计院有限公司,浙江金华321000

出　　处：《第四纪研究》2022年第3期843-857,共15页Quaternary Sciences

基　　金：国家自然科学基金项目(批准号:42041006和41672285);陕西省自然科学基础研究计划项目(批准号:2018JQ4003)共同资助。

摘　　要：河流裂点的发育是瞬时不均衡地貌系统最为典型的特征之一,而引发地表破裂的地震活动是造成河流裂点形成的主要成因之一,在河流纵剖面调整的过程中裂点会不断地向上游迁移,以达到新的均衡状态,因此通过识别活动断层上游河道纵剖面中的河流裂点序列可以反推该断层的强震活动历史。秦岭北缘断裂是限定秦岭山体和渭河盆地的重要边界断裂,受制于技术方法和自然条件,对于该断裂全新世地震活动历史一直有待突破。本研究在前人对秦岭北缘断裂分段性研究的基础上选取最为活跃的中段(眉县-蓝田县),基于资源三号卫星立体像对制作了5m分辨率和高程精度1.5m的数字高程模型,在此基础上提取了46条横穿秦岭北缘断裂的河床纵剖面,共识别了108个由断层活动导致的河流裂点。通过分析推断最新一级河流裂点的形成与公元前1000a的地震相关,进而利用河流裂点的后退速率推断出第2级河流裂点和第3级河流裂点形成的时间距今5624~7425a和8432~10691a,如果认为上述河流裂点均由地震所致,那么河流裂点的形成时间就可以代表地震的发生时刻,表明秦岭北缘断裂具有准周期的发震特点,发震周期为2800~4000a。这一结果与前人针对秦岭北缘断裂古地震研究结果基本一致。此外,所识别出的三级河流裂点陡坎高度分别为约4.7m、5.1m和5.2m,近乎一致的陡坎高度表明秦岭北缘断裂过去3次地震的震级大小相近,根据平均4.95±0.29m的陡坎高度所计算得到秦岭北缘断裂过去3次地震的震级大小为M_(W)=7.65±0.02。这一研究为认识秦岭北缘断裂的强震活动性提供了地貌证据约束,也为研究基岩山区断裂的古地震问题提供了新的途径。Knickpoint is one of the most typical property of transient landform systems,ground-rupturing earthquakes can generate tectonic knickpoints of streams across active fault zones.In the adjustment of the longitudinal profile of the stream,the knickpoint will migrate upstream at some rate due to continuous retrogressive erosion.Therefore,by identifying the sequence of the knickpoints in the longitudinal profile of the upstream channel of the active fault,the history of strong earthquake of the fault can be deduced.The Qinling north piedmont normal fault(QPF)is an important boundary fault that defines the Qinling Mountains and the Weihe Basin,but for a long time,the history of Holocene seismic activity on the fault is unclear.We studied the knickpoints along the QPF,and demonstrate that analysis of knickpoints shows evidence for three paleoearthquakes in the QPF.First,we identified knickpoints in bedrock upstream of the QPF using high-resolution DEMs derived from ZY-3 stereo images and the stream-gradient method.After excluding non-faulting knickpoints,108 knickpoints were identified in 46 bedrock reaches upstream from the QPF.Analysis of the most recent knickpoints caused by the 1000 BC Earthquake allowed for local calibration of the retreat rates.Applying these retreat rates across the study area allows for the estimation the age of other knickpoints,and constrains the age ranges of two knickpoint groups to be 5624~7425aB.P.and 8432~10691aB.P.If we believe that these knickpoint are caused by earthquake,then their formation time can represent the age of the earthquake,which indicating QPF obey a characteristic earthquake model with recurrence period of 2800~4000a.The knickpoints along the QPF obey the parallel retreating model in which knickpoint morphology was roughly maintained during retreat,so the heights of knickpoints represent the coseismic vertical displacements generated by the earthquakes along the QPF.The three earthquake events had similar vertical offsets of 4.7 m,5.1 m and 5.2 m,respectively,and the ne

关 键 词：河流裂点 秦岭北缘断裂 古地震 资源3号 汾渭地震带 

分 类 号：P546[天文地球—构造地质学]