| 龙门山南段芦山震区浅层沉积与构造变形——对深部发震构造的约束 |
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| 引用本文： | 鲁人齐,徐锡伟,何登发,刘波,谭锡斌,张学丰,李英强,王振南.龙门山南段芦山震区浅层沉积与构造变形——对深部发震构造的约束[J].地球物理学报,2017,60(8):2924-2934. |
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| 作者姓名： | 鲁人齐 徐锡伟 何登发 刘波 谭锡斌 张学丰 李英强 王振南 |
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| 作者单位： | 1. 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;2. 中国地质大学(北京) 能源学院, 北京 100083;3. 北京大学地球与空间科学学院, 北京 100871 |
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| 基金项目： | 国家自然科学基金（41202142，41572117，41672123）和中国地震局地质研究所基本科研业务专项（IGCEA1422）联合资助. |
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| 摘 要： | 2013年4月20日在龙门山南段发生M_W6.7强震,造成重大人员伤亡和财产损失.芦山地震发生后,针对发震断层是高角度还是低角度断层?断层的归属、性质和地震构造模型等问题,一直存在不同的认识和争议.本次研究采用了芦山震区的三条高精度二维人工地震反射剖面,结合区域地质、钻井资料,对芦山震区浅层沉积与构造变形进行综合解释;研究同时综合了震源机制解、小震重定位结果以及深地震探测剖面,并结合龙门山地区古生代以来的构造演化史,对震区地质构造进行解析.研究认为龙门山南段主要发育了三套不同层次的滑脱层并控制了上地壳形变,呈现多层滑脱、多期变形、构造叠加的复杂特征.2013年芦山地震的主要活动断层发育在深部约20 km滑脱层之上,倾向NW、倾角较陡大约在45°~50°,并产生反冲断层形成Y字状结构.地震地质解释表明,芦山地震的同震活动断层没有突破中生界和新生界,并非先前认为的双石—大川断裂(F4)或山前大邑隐伏断裂(F6);芦山地震的发震断层为一基底盲冲断层;深地震反射结果进一步揭示芦山地震的发震断层为一早期(古生代)形成的正断层.研究认为芦山地震发震构造符合简单剪切断层转折褶皱模型(Simple-shear Fault-Bend Fold),2013年芦山地震为一次非特征型地震.晚新生代以来在青藏高原向四川盆地强烈挤压持续作用下,早期正断层重新活动并产生了芦山地震.这种深部隐伏断层活化产生的特殊型地震,无疑增加了龙门山地区地震灾害的风险和不确定性.
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| 关 键 词： | 地震解释 滑脱层 构造变形 断层转折褶皱 芦山地震 龙门山 |
| 收稿时间： | 2016-12-04 |
Shallow sedimentation and tectonic deformation in the southern Longmen Shan: Constraints on the seismotectonics of the 2013 Lushan MW6.7 earthquake |
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| LU Ren-Qi,XU Xi-Wei,HE Deng-Fa,LIU Bo,TAN Xi-Bin,ZHANG Xue-Feng,LI Ying-Qiang,WANG Zhen-Nan.Shallow sedimentation and tectonic deformation in the southern Longmen Shan: Constraints on the seismotectonics of the 2013 Lushan MW6.7 earthquake[J].Chinese Journal of Geophysics,2017,60(8):2924-2934. |
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| Authors: | LU Ren-Qi XU Xi-Wei HE Deng-Fa LIU Bo TAN Xi-Bin ZHANG Xue-Feng LI Ying-Qiang WANG Zhen-Nan |
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| Institution: | 1. Key Laboratory of Active Tectonics and Volcano, Institute of Geology, China Earthquake Administration, Beijing 100029, China;2. College of Energy Resources, China University of Geosciences, Beijing 100083, China;3. School of Earth and Space Science, Peking University, Beijing 100871, China |
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| Abstract: | The April 20, 2013 Lushan MW6.7 earthquake occurred in the southern Longmen Shan (LMS) causing heavy casualties and property damage. After this event, whether its causative fault is a high-angle or low-angle one, and the characteristics, attributes, and the seismotectonic model of this earthquake remain debated. In this study, three high-resolution artificial seismic reflection profiles were combined with near-surface geological data and well drilling data to interpret the shallow sedimentation and tectonic deformation of the Lushan earthquake area. We also integrated the focal mechanism solutions, earthquake relocation, and a recent deep seismic reflection profile, in combination with the tectonic evolution since Paleozoic, to analyze the geology of the southern LMS. The results suggest that three major detachments control the tectonic deformation of the upper crust in the LMS and western Sichuan Basin (SB), resulting in multiple superimposed deformation events. The coseismic active fault dips to the northwest at approximately 45°~50° at depths of 20 km, forming a Y-shaped structure. Seismic interpretations suggest that the seismogenic fault of the Lushan earthquake is a typical basement blind fault that does not penetrate into the overlying Mesozoic and Cenozoic units, and is not the Shuangshi-Dachuan fault (F4) or the frontal Dayi buried fault (F6). Deep seismic data illustrate the syndepositional characteristics of the seismogenic fault. Our study further demonstrates that the seismogenic slip occurred on a reactivated pre-existing normal fault older than Triassic age that triggered earthquakes during the Late Cenozoic. The 2013 Lushan earthquake was not a characteristic earthquake, and the structure of the Lushan earthquake zone conforms to the simple-shear fault-bend fold. Since the Late Cenozoic, with the strong and on-going compression of the Tibetan Plateau to the Sichuan Basin, the early-period normal faults were reactivated after inversion and triggered the Lushan earthquakes. These concealed and reactivated faults increase the potential risk of major earthquakes in the Longmen Shan and the western Sichuan Basin. |
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| Keywords: | Seismic interpretation Detachment Structural deformation Fault-Bend Fold Lushan earthquake Longmen Shan |
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