SEISMOLOGY AND GEOLOGY ›› 2016, Vol. 38 ›› Issue (3): 523-545.DOI: 10.3969/j.issn.0253-4967.2016.03.003

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USING DEFORMED FLUVIALTERRACES OF THE QINGYIJIANG RIVER TO STUDY THE TECTONIC ACTIVITY OF THE SOUTHERN SEGMENT OF LONGMENSHAN FAULT ZONE

SU Peng1,2, TIAN Qin-jian1, LIANG Peng1, LI Wen-qiao1, WANG Lin1   

  1. 1 Key Laboratory of Earthquake Prediction, Institute of Earthquake Science, China Earthquake Administration, Beijing 100036, China;
    2 Key Laboratory of Active Tectonics and Volcano, Institute of Geology, China Earthquake Administration, Beijing 100029, China
  • Received:2014-10-29 Revised:2015-11-16 Online:2016-09-20 Published:2016-10-15

基于青衣江变形河流阶地研究龙门山断裂带南段的构造活动性

苏鹏1,2, 田勤俭1, 梁朋1, 李文巧1, 王林1   

  1. 1 中国地震局地震预测研究所, 地震预测重点实验室, 北京 100036;
    2 中国地震局地质研究所, 活动构造与火山重点实验室, 北京 100029
  • 通讯作者: 田勤俭,研究员,E-mail:tianqj@263.net
  • 作者简介:苏鹏,男,1989年生,2015年于中国地震局地震预测研究所获构造地质学专业硕士学位,现为中国地震局地质研究所在读博士研究生,研究方向为构造地貌,电话:010-62009127,E-mail:supeng2014@icloud.com。
  • 基金资助:

    中国地震局地震预测研究所基本科研业务专项(2013IES010101,2014IES010104)、高分光学遥感地震构造提取示范应用项目(31-Y30B09-9001-13/15-07)与中国地震局地质研究所基本科研业务专项(IGCEA1416)共同资助

Abstract:

On 20 April 2013, a destructive earthquake, the Lushan MS7.0 earthquake, occurred in the southern segment of the Longmenshan Fault zone, the eastern margin of the Tibetan plateau in Sichuan, China. This earthquake did not produce surface rupture zone, and its seismogenic structure is not clear. Due to the lack of Quaternary sediment in the southern segment of the Longmenshan fault zone and the fact that fault outcrops are not obvious, there is a shortage of data concerning the tectonic activity of this region. This paper takes the upper reaches of the Qingyijiang River as the research target, which runs through the Yanjing-Wulong Fault, Dachuan-Shuangshi Fault and Lushan Basin, with an attempt to improve the understanding of the tectonic activity of the southern segment of the Longmenshan fault zone and explore the seismogenic structure of Lushan earthquake.
In the paper, the important morphological features and tectonic evolution of this area were reviewed. Then, field sites were selected to provide profiles of different parts of the Qingyijiang River terraces, and the longitudinal profile of the terraces of the Qingyijiang River in the south segment of the Longmenshan fault zone was reconstructed based on geological interpretation of high-resolution remote sensing images, continuous differential GPS surveying along the terrace surfaces, geomorphic field evidence, and correlation of the fluvial terraces.
The deformed longitudinal profile reveals that the most active tectonics during the late Quaternary in the south segment of the Longmenshan Fault zone are the Yanjing-Wulong Fault and the Longmenshan range front anticline. The vertical thrust rate of the Yanjing-Wulong Fault is nearly 0.6~1.2mm/a in the late Quaternary. The tectonic activity of the Longmenshan range front anticline may be higher than the Yanjing-Wulong Fault. Combined with the relocations of aftershocks and other geophysical data about the Lushan earthquake, we found that the seismogenic structure of the Lushan earthquake is the range front blind thrust and the back thrust fault, and the pop-up structure between the two faults controls the surface deformation of the range front anticline.

Key words: the southern segment of the Longmenshan Fault zone, Lushan MS7.0 earthquake, longitudinal profile of river terraces, tectonic activity, seismogenic structure, Yanjing-Wulong Fault, Dachuan-Shuangshi Fault

摘要:

龙门山断裂带南段第四纪沉积差,断层出露不明显,晚第四纪构造活动性资料零星。为了提高对龙门山断裂带南段构造活动性的认识,探索芦山地震的发震构造,文中在分析龙门山断裂带南段的地貌以及构造演化的基础上,对跨盐井-五龙断裂、大川-双石断裂和芦山盆地的青衣江不同段的6级河流阶地进行了差分GPS连续测量和细致研究,结合对高分辨率航拍影像的地质解译,得到了龙门山断裂带南段青衣江各段的河流阶地横剖面,通过不同河段河流阶地的对比分析,建立了龙门山断裂带南段青衣江河流阶地纵剖面。通过对河流阶地的变形分析,发现龙门山断裂带南段晚第四纪以来,盐井-五龙断裂的平均垂向断错速率为0.6~1.2mm/a,大川-双石断裂没有明显的垂向活动,芦山地震的发震断层控制的山前褶皱最新活动。结合龙门山断裂带南段的地壳深部结构资料和芦山地震的精定位余震资料等,认为芦山地震的发震构造不是大川-双石断裂,而是龙门山断裂带南段的山前盲逆断层和反冲断层。

关键词: 龙门山断裂带南段, 芦山MS7.0地震, 河流阶地纵剖面, 构造活动性, 发震构造, 盐井-五龙断裂, 大川-双石断裂

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