| 深反射剖面揭示的芦山7.0级地震发震构造 |
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| 引用本文： | 王夫运,赵成彬,酆少英,姬计法,田晓峰,魏学强,李怡青,李吉昌,花鑫升.深反射剖面揭示的芦山7.0级地震发震构造[J].地球物理学报,2015,58(9):3183-3192. |
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| 作者姓名： | 王夫运 赵成彬 酆少英 姬计法 田晓峰 魏学强 李怡青 李吉昌 花鑫升 |
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| 作者单位： | 中国地震局地球物理勘探中心, 郑州 450002 |
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| 基金项目： | 中国地震局四川省芦山"4.20"7.0级强烈地震科学考察项目、国家自然科学基金项目(41340007)和地震科技星火计划项目(XH15059)共同资助. |
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| 摘 要： | 芦山地震发生在龙门山断裂带前缘.关于芦山地震的发震断层,有的认为是前山断裂——双石—大川断裂,有的认为是山前断裂——大邑断裂拟或其他隐伏断裂,发震断裂究竟是哪条断裂以及芦山地震是不是汶川地震的余震?目前仍存在较大争议.震后穿过芦山地震区完成了一条长近40km的深地震反射剖面,以确定芦山地震的发震构造.反射剖面显示浅部褶皱和断裂构造发育,在上地壳存在6条逆冲断裂,下地壳存在一条非常明显的变形转换带,在深度16km左右还存在一个滑脱层,浅部的6条断裂最终都归并到该滑脱层上.参考主余震精定位结果,芦山地震的发震断裂应该是位于双石—大川断裂和大邑断裂之间的隐伏断裂F4,F2和F3断裂受控于发震断裂而活动,形成剖面上"Y"字型余震分布现象.隐伏断裂F4属山前断裂,不是前山断裂,因此芦山地震不是汶川地震的余震.
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| 关 键 词： | 芦山地震 发震断裂 隐伏断裂 双石-大川断裂 大邑断裂 深地震反射剖面 |
| 收稿时间： | 2014-10-30 |
Seismogenic structure of the 2013 Lushan MS7.0 earthquake revealed by a deep seismic reflection profile |
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| WANG Fu-Yun,ZHAO Cheng-Bin,FENG Shao-Ying,JI Ji-Fa,TIAN Xiao-Feng,WEI Xue-Qiang,LI Yi-Qing,LI Ji-Chang,HUA Xin-Sheng.Seismogenic structure of the 2013 Lushan MS7.0 earthquake revealed by a deep seismic reflection profile[J].Chinese Journal of Geophysics,2015,58(9):3183-3192. |
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| Authors: | WANG Fu-Yun ZHAO Cheng-Bin FENG Shao-Ying JI Ji-Fa TIAN Xiao-Feng WEI Xue-Qiang LI Yi-Qing LI Ji-Chang HUA Xin-Sheng |
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| Institution: | Geophysical Exploration Center, China Earthquake Administration, Zhengzhou 450002, China |
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| Abstract: | The 2013 Lushan earthquake occurred in the front of the Longmen Shan fault zone. What is the seismogenic structure of this event remains unclear. Some researchers suggest that it is the front-range fault, the Shuangshi-Dachuan fault, while others claim that it is the piedmont fault, the Dayi fault or other buried faults. Which is the real seismogenic fault and whether the Lushan earthquake is an aftershock of the 2008 Wenchuan mega event? It is still a big controversy. To address this issue, we have deployed a 40 km-long deep seismic reflection profile in the NW-SE direction through the Lushan earthquake area. The profile starts from Muping town, Baoxing county and ends in Xindian town, Mingshan district. The survey used dynamite sources with 24~30 kg charges at a depth of 25 m. The French SN408UL seismograph was employed to collect seismic signals. The length of the seismic record was designed as 20 s with a 4-ms sampling interval. The spread geometry has 800 recording channels, 30 m station spacing and 67-folds. The FOCUS and GRISYS seismic reflection data processing system are used for data processing, including pre-stack denoising, dip stack, post-stack denosing and bending line treatment, which permitted to yield good stack results with high SNR.
The TWT time profile shows that there are 6 thrusting faults in the upper crust (above the 10 km) where folds and faults are developed. There is a low-angle detachment layer at the depth of 16 km, where the 6 faults aforementioned eventually merge into one. It is the decoupling of detachment layer that separates the faults in the upper crust from the deep large fault in the lower crust, so the Lushan earthquake occurrence has nothing to do with the deep large fault of the lower crust. Below the depth of 10 km, the crustal structure is relatively simple, where there is only one deep large fault cutting the interface between the upper and lower crust and the Moho interface. Fault features and the fault combination form of the upper crust show that the seismogenic fault of the Lushan earthquake should be the buried fault F4 between the Shuangshi-Dachuan fault and Dayi fault. The faults F2 and F3 are active because of control from the seismogenic fault, which led to a "Y-shaped" aftershock distribution. The buried fault F4 is the piedmont fault rather than the front-range fault, so the Lushan earthquake is not the aftershock of the Wenchuan earthquake. |
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| Keywords: | Lushan earthquake Seismogenic fault Buried fault Shuangshi-Dachuan fault Dayi fault Deep seismic reflection profile |
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