SEISMOLOGY AND GEOLOGY ›› 2015, Vol. 37 ›› Issue (2): 440-454.DOI: 10.3969/j.issn.0253-4967.2015.02.008

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LATE QUATERNARY ACTIVITY OF ZHUMA FAULTON THE NORTH SEGMENT OF DALIANGSHAN FAULT ZONE

SUN Hao-yue, HE Hong-lin, WEI Zhan-yu, GAO Wei   

  1. Key Laboratory of Active Tectonics and Volcano, Institute of Geology, China Earthquake Administration, Beijing 100029, China
  • Received:2014-07-07 Revised:2015-01-09 Online:2015-06-20 Published:2015-08-19

大凉山断裂带北段东支——竹马断裂晚第四纪活动性

孙浩越, 何宏林, 魏占玉, 高伟   

  1. 中国地震局地质研究所, 活动构造与火山重点实验室 100029
  • 通讯作者: 何宏林,研究员,E-mail:honglinhe123@vip.sina.com
  • 作者简介:孙浩越,男,1986年生,2009年于成都理工大学获地质学专业学士学位,现为中国地震局地质研究所博士研究生,研究方向为活动构造与构造地貌,电话:010-62009101,E-mail:sunhaoyue0312@sina.com。
  • 基金资助:

    财政部重大专项(201108001)资助。

Abstract:

Daliangshan Fault Zone (DFZ) constitutes a significant part of the eastern boundary of Sichuan-Yunnan Active Block (SYAB). Studying the activity and slip rate of this fault zone is not only of great significance in understanding the movement of tectonic blocks and crustal deformation at the southeastern margin of Tibetan plateau, but also valuable in seismic hazard assessment and mid- and long-term forecasting of earthquake in west Sichuan. Zhuma Fault is the east branch of northern segment of DFZ which consists of six branch faults. Based on the detailed field investigations and through the accurate RTK (GPS) surveying and dating of the displaced landforms, we find that Zhuma Fault has been active since Holocene with a dominant left-lateral movement pattern and constrain its slip rate to be 1.5~3.1mm/a. Furthermore, a trench was excavated which reveals two paleoearthquakes occurring within(50.3±5.7)~30ka BP and 30~(17.4±1.2)ka BP, respectively from the stratigraphic evidence and OSL dating data. Although the slip rate on the Zhuma Fault is a little smaller than that on the southern segment of DFZ, we suggest uniform slip rates on the DFZ in consideration of the existence of another branch faults on the northern segment. The similar slip rate on DFZ to those on Anninghe Fault Zone (AFZ) and Zemuhe Fault Zone (ZFZ) implies that DFZ possesses a comparable partitioning component of displacement of Xianshuihe-Xiaojiang Fault System (XXFS) to AFZ and ZFZ. Further, the sum of slip rates on central segment of XXFS shows a good agreement with that on northern or southern segment. Thus, it is suggested that the DFZ not only patches the gap generated by the deviation of the strikes of AFZ and ZFZ from the average strike of XXFS, thus, making it a perfect small arc on earth, but also covers the deficiency in displacement and slip rate between central segment and northern or southern segment to maintain the XXFS to be harmonious. Moreover, according to the sedimentary characteristics and dating data, it is revealed that the alluvial-proluvial fans along the Zhuma Fault are formed by the glacial melt water in the last deglaciation after the Younger Dryas cooling event and such landforms could be widely developed in this region.

Key words: Daliangshan Fault zone, late Quaternary, activity, slip rate, paleoearthquake

摘要:

大凉山断裂带是川滇菱形活动块体东边界的重要组成部分, 其活动习性和滑动速率对于了解青藏高原东南缘的块体运动和构造变形具有重要的理论意义, 同时对于该地区地震危险性评价和地震中长期预测有着重要的应用价值。大凉山断裂带由6条分支断裂构成, 竹马断裂是其北段的一条分支。文中在详细野外调查的基础上, 通过典型构造地貌的高精度GPS测量和断错时间的约束, 得出竹马断裂是一条以左旋走滑为主的全新世活动断裂, 全新世以来的水平滑动速率为1.5~3.1mm/a; 利用古地震探槽揭示出竹马断裂的2次古地震事件时间分别为(50.3±5.7)~30ka BP和30~(17.4±1.2)ka BP。考虑到断裂带北段还存在一条与竹马断裂平行的分支断裂——公益海断裂, 大凉山断裂带北段的滑动速率与南段基本一致。鲜水河-小江断裂系中段在大凉山断裂带上分配的滑动速率与并行的安宁河断裂带和则木河断裂带也大体相当, 断裂系中段的滑动速率之和与南北两段的速率大致吻合。大凉山断裂带的存在使断裂系在几何上成为一个完整的弧形构造, 也弥补了中段滑动速率的亏损, 使各段的滑动保持协调一致。此外, 沿竹马断裂大量发育的冲洪积台地, 根据沉积特征和测年结果, 认为是新仙女木事件后末次冰消期的冰川融水形成的冰水堆积, 类似的地貌面可能广泛分布于青藏高原东南缘。

关键词: 大凉山断裂带, 晚第四纪, 活动性, 滑动速率, 古地震

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