龙门山南段前缘地区活褶皱-逆断层运动学机制——以芦山地震为例

李敬波1， 李勇1， 周荣军2，颜照坤1， 闫亮1， 郑立龙1， 杨聿强1， 任聪3

(1.成都理工大学油气藏地质及开发工程国家重点实验室，四川 成都610059；

2.四川省地震局工程地震研究院，四川 成都610041； 3.中国石油西南气田分公司勘探事业部，四川，成都610047)

摘要：2013年4月20日发生在龙门山南段的芦山MS7.0地震是继发生在龙门山中北段的汶川MS8.0地震之后的又一次强震。本文通过震后地表变形特征、余震分布、震源机制解、石油地震勘探剖面、历史地震数据等资料，结合前人对龙门山南段主干断裂、褶皱构造特征的研究以及野外实地考察，应用活动褶皱及“褶皱地震”的相关理论，初步分析芦山地震的发震构造模式。认为芦山地震为典型的褶皱地震，发震断裂为前山或山前带一隐伏断裂。构造挤压产生的地壳缩短大部分被褶皱构造吸收。认为龙门山南段前缘地区具有活褶皱-逆断层的运动学特征，表明龙门山逆冲作用正向四川盆地内部扩展。

关键词：芦山地震； 龙门山南段； 褶皱地震； 隐伏断裂

收稿日期：*2014-04-21

基金项目：国家自然科学

作者简介：李敬波(1990-)，男(汉族)，硕士研究生，构造地质学专业.E-mail：jingbo_li1990@sina.com

中图分类号:P135.2文献标志码：A

DOI:10.3969/j.issn.1000-0844.2015.01.0202

AnalysisofKinematicMechanismofActiveFold-Thrust

FaultinfrontoftheSouthernLongmenshan

Mountain:ACaseStudyoftheLushanEarthquake

LIJing-bo1， LI Yong1, ZHOU Rong-jun2， YAN Zhao-kun1，

YANLiang1， ZHENG Li-long1， YANG Yu-qiang1， REN Cong3

(1. State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation，Chengdu University

of Technology，Chengdu，Sichuan610059，China；

2.Institute of Engineering Seismology，Earthquake Administration of Sichuan Province，Chengdu，Sichuan610041，China；

3.Exploration Division of Southwest Oil and Gas Field Company，CNPC，Chengdu，Sichuan，Chengdu610041，China)

Abstract：The Lushan earthquake (MS7.0，April 20，2013)that occurred in the southern segment of the Longmenshan Fault was another destructive earthquake that followed the Wenchuan (MS8.0) earthquake that occurred in the middle-northern section of the Longmenshan Fault.The epicenter was 30.3° N，103.0° E at a depth of about 13 km.The Longmenshan Fault is located on the eastern side of the Qinghai-Tibetan Plateau，which marks an area of abrupt geological, geomorphological，and climatological changes in western China.There are three main faults in the southern section of the Longmenshan Fault，i.e.，the Gengda-Longdong，Yanjing-Wulong，and Shuangshi-Dachuan faults.The research area encompassed three levels of geomorphic units that from west to east comprised landforms of the Qinghai-Tibetan Plateau，the alpine zone of the southern section of the Longmenshan Fault，and a piedmont alluvial plain area (Southwest of Chengdu Basin).The three main faults are located in the alpine zone in the southern section of the Longmenshan Fault，which crosses the Qingyi River.In this paper，a preliminary analysis of the seismogenic tectonic mechanism of the Lushan earthquake is presented based on data of post-earthquake surface deformational characteristics，aftershocks，focal mechanism solutions，and oil seismic exploration profiles.The results indicate that the Lushan earthquake was a typical folding earthquake，the seismogenic fault of which might have been the buried fault in front of the Longmenshan Mountain.The shortening produced by tectonic compression can be absorbed by folding.Considering the Lushan earthquake as an example，analysts suggest that the southern segment of the Longmenshan frontal region has the kinematic characteristics of an active fold-thrust fault，which is indicated by the enlarged Longmenshan thrusting towards the inner Sichuan Basin.Young，rapidly growing active folding is related not only to the earthquake location and seismic structure but also to the product of continuous earthquakes.In the southern Longmenshan thrust belt，at the same time as the late-Cenozoic faulting，the thrust belt entered the western Sichuan Basin，and the Longquanshan，Xiongpo，and Qiongxi faults were formed. From the Shuangshi fracture eastward to the Longquanshan tectonic belt，there are several rows of fault-related folds over one decollement at the bottom of the middle and lower Triassic Plaster gypsum stratum.Research has shown that the Lushan earthquake was an active fault-folding earthquake that differed from the Wenchuan earthquake.These active folds with stick-slip mechanisms are called “earthquake drapes”. Traditionally，it has been considered that fold structures are products of homogeneous stress states，and therefore，earthquakes that occur in active folds are considered non-dangerous.However，the the Lushan folding earthquake caused great damage.In the southern segment of the Longmenshan Fault and its front areas，there is less chance of a great earthquake like the Wenchaun earthquake occurring；however，stress will concentrate in the Sichuan Basin by the detachment fault，and therefore，a watchful eye must be maintained on the faults in that basin，especially the Pujing-Xinjin fault.

Keywords：Lushanearthquake；thesouthernsectionofLongmenshanfault；foldingearthquake；buriedfault

0引言

2013年4月20日，在四川省雅安市芦山县境内发生了MS7.0地震，震中为30.3°N，103.0°E，震源深度约13 km(中国地震台网中心，2013)。此次地震发生在龙门山推覆构造带南段，是继2008年龙门山地震带汶川MS8.0特大地震后的又一次强震。芦山地震震中所处的构造单元、余震分布规律以及震后地表变形特征等与汶川地震相比均存在很大差异，这种差异引起了地学界对芦山地震是否为2008年汶川地震余震的激烈争论[1-6]。……