摘要
采用深地震反射剖面探测,结合地表地质信息,本文对芦山地区的地壳结构、深浅构造和隐伏活动断裂进行了分析.研究结果表明:该区上地壳结构特征清晰,深度约为15km左右;区内断裂由于受青藏高原向东南方向的推挤和坚硬的四川盆地阻挡的联合作用均属逆冲断裂,其中双石—大川断裂以低角度向深部延伸,主要表现为纯逆冲的运动学性质,并与周边小断裂共同组成叠瓦状断层构造.而广元—大邑断裂为上陡下缓式逆冲断裂,与其六条分支断裂共同组成了"正花状"构造,断裂活动是以逆冲为主,并伴随着小的水平滑动,是一条斜向逆冲的断裂.在芦山地震发震断裂的2km范围内推测存在一陡一缓两条断裂,并根据三者形态推测其在18km或以上收敛到一起并向深部延伸,从而使它们在芦山地震中被同时激活.研究结果揭示了研究区近地表活动断裂和地壳深部构造之间的关系,为进一步研究龙门山断裂带的深部构造环境、深浅构造关系以及断裂的活动性提供了有利的依据.
A deep seismic reflection profiling was collected to probe the fine crustal structure of the Lushan area,Sichuan Province.The purpose is to reveal the relationship between the shallow and deep structures,and the geometry and kinetics of the blind active faults using the seismicprofiling and surface geology.The results show that the crust of the study area is characterized by a distinct structure of upper crust with thickness about 15 km.The nature of the faults is inferred to be thrusting in the region due to the pushing of the crustal material of the Tibetan plateau into the southeast part of the rigid Sichuan basin.The Shuangshi-Dachuan fault stretches from the surface to the deep crust at a low angle,and is dominated by thrusting in a form of imbricate structure with small-scale faults nearby.Whereas the Guangyuan-Dayi fault is of a positive flower structure with a listric shape,consisting of six branches.Its movement is dominated by thrusting with gentle horizontal slip.We also speculated there are two faults,one is with steep dip and another is with gentle dip,2km to near the seismogenic fault of the Lushan earthquake.According to the forms of the three faults,we suggested that they convergence at the depth of 18 km and extend downward,and were activated during the occurrence of the Lushan earthquake.The results reveal the relationship between the subsurface active faults and the deep crustal structure,which would shed a light on the further research of the deep structure,the relationship between shallow and deep structures,and the fault activity of the whole Longmenshan fault zone.
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
2016年第9期3248-3259,共12页
Chinese Journal of Geophysics
基金
国家科技专项<汶川地震断裂带科学钻探项目>(WFSD)
中国地质调查局项目<龙门山构造带三维地质填图>(1212011220265)联合资助
关键词
龙门山断裂带南段
深地震反射剖面
地壳结构和构造
芦山地震
South segment of Longmenshan fault zone
Deep seismic reflection profile
Crustal structure
Lushan earthquake
