秦岭北缘断裂带的重要分支——桃川-户县断层的浅部结构与第四纪活动性  

SHALLOW STRUCTURE AND QUATERNARY ACTIVITY OF THE TAOCHUAN-HUXIAN FAULT,THE SUB-STRAND OF THE NORTHERN QINLING FAULT ZONE

作　　者：杨晨艺 李晓妮[1] 冯希杰[1] 黄引弟 裴跟弟 YANG Chen-yi;LI Xiao-ni;FENG Xi-jie;HUANG Yin-di;PEI Gen-di(Shaanxi Earthquake Agency,Xi’an 710068,China;CCTEG Xi'an Research Institute,Xi’an 710077,China)

机构地区：[1]陕西省地震局,西安710068 [2]中煤科工西安研究院(集团有限公司),西安710077

出　　处：《地震地质》2023年第2期464-483,共20页Seismology and Geology

基　　金：陕西省自然科学基础研究计划青年项目(2022JQ-298);陕西省“十二五”重点项目“关中地区大震危险性评价”共同资助。

摘　　要：秦岭北缘断裂带是渭河盆地南缘重要的活动构造,含有多条分支断层,其中近EW向的桃川-户县断层位于该断裂带的北侧,其东段隐伏于渭河盆地内。已有研究对该断层隐伏段的中段开展了浅层人工地震勘探,并推断其为正断兼走滑运动性质的晚更新世活动断层,但未能确定断层最晚活动的年代与活动速率。文中通过开展新的浅层地震勘探和钻孔联合剖面探测,进一步研究了桃川-户县断层西段(太白盆地段)与东段(渭河盆地隐伏段)的浅部结构构造和几何展布、第四纪活动的最晚时代及活动速率。探测剖面揭示出桃川-户县断层的西段可向W延伸至少20km至太白盆地,而东段自眉县起延入渭河盆地,经周至、户县,隐伏于渭河盆地第四系中。断层西段在太白盆地断错早第四系及下伏结晶基底,控制了太白盆地南缘,其N倾的正断作用断错第四系约300m,断层带内保留老的逆冲构造残余。断层东段(渭河盆地隐伏段)在周至和户县附近的主断面倾向N,断层带分别表现为宽约6km的断陷带和宽约4km的阶梯状构造带,断错了上更新统顶界;在渭河盆地南缘,断层断错全新统标志层黑垆土S0,垂直断距为4~5m,对应的全新世活动速率为0.4~1.3mm/a。综合浅层地震勘探、钻孔探测及地面地质调查结果分析认为,桃川-户县断层东段的活动性明显强于西段,这可能是由于东段并入渭河盆地构造带,成为一级活动地块边界带的一部分所致。桃川-户县断层是秦岭北缘断裂带的重要组成部分,其控制了渭河盆地南缘的构造活动。The northern Qinling fault zone is an important active structure in the southern margin of the Weihe Graben Basin,containing many branch faults,of which the near EW striking Taochuan-Huxian Fault is located on the northern side of the fault zone,and the eastern segment is buried in the Weihe Graben Basin.Shallow seismic exploration has been carried out on the middle part of the buried segment of this fault,and the fault inferred to be a late Pleistocene fault with normal strike-slip movement,but the age and rate of the latest activity have not been determined.By conducting new shallow seismic and drilling joint exploration,we further study the shallow structure,the geometric distribution,the latest activity era and the slip rate in the Quaternary in the two segments of the Taochuan-Huxian Fault.The profile of shallow seismic exploration line TB1 reveals that the west segment of the Taochuan-Huxian Fault with NEE trend can extend at least 20km westward from Taochuan Town.The main fault plane dips to N,and the normal-slip movement has faulted the Quaternary bottom boundary and the underlying crystalline basement in the Taibai Basin.The vertical offset of the Quaternary bottom boundary is about 300m,and the remnants of the old thrust structure are still preserved in the fault zone.The shallow seismic reflection lines ZZ1 and YX1-2 reveal the location of the eastern Taochuan-Huxian Fault with the EW striking buried in the Quaternary of the Weihe Graben Basin in Zhouzhi and Huxian.The main fault plane dips to N,and the fault zone is represented by a fault depression zone of about 6km wide and a stepped structure of about 4km wide respectively.The fault up-breakpoints on both profiles offset the bottom boundary of the Holocene in the Weihe Graben Basin.The drilling joint profile exploration applied at Tanjiazhai in Zhouzhi County and Xiashimasi in Meixian County show that the Taochuan-Huxian Fault is distributed in the junction of the southern Weihe Granben Basin and the Qinling Mountains,where the Holocene marker laye

关 键 词：活动断层 浅层地震探测 钻孔联合剖面探测 桃川-户县断层 全新世活动速率 

分 类 号：P315.2[天文地球—地震学]