| 2017年8月8日九寨沟M7.0地震及余震震源机制解与发震构造分析 |
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| 引用本文： | 易桂喜,龙锋,梁明剑,张会平,赵敏,叶有清,张致伟,祁玉萍,王思维,宫悦,乔惠珍,汪智,邱桂兰,苏金蓉.2017年8月8日九寨沟M7.0地震及余震震源机制解与发震构造分析[J].地球物理学报,2017,60(10):4083-4097. |
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| 作者姓名： | 易桂喜 龙锋 梁明剑 张会平 赵敏 叶有清 张致伟 祁玉萍 王思维 宫悦 乔惠珍 汪智 邱桂兰 苏金蓉 |
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| 作者单位： | 1. 四川省地震局, 成都 610041;
2. 四川赛思特科技有限责任公司, 成都 610041;
3. 中国地震局地质研究所地震动力学国家重点实验室, 北京 100029 |
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| 基金项目： | 国家自然科学基金（41574047），四川赛思特科技有限责任公司西部大开发优惠政策节税资金投资项目（XDK2015001），四川省九寨沟7.0级地震科学研究专项，川滇地区运动学模型和重点构造部位动力学模型构建（20150115），四川省外国专家局引智项目（S201637）及2017年地震监测预报跟踪专项共同资助. |
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| 摘 要： | 2017年8月8日在青藏高原东缘四川省九寨沟县发生M7.0级强烈地震，极震区烈度达Ⅸ度，但无明显地表破裂，一定程度上限制了发震构造的确定和后续地震危险性判定.本文基于截止至2017年8月14日的地震资料，采用多阶段定位方法，对主震及余震进行了重新定位，同时，利用CAP波形反演方法，获得了M7.0主震与13次ML ≥ 4.0级余震的震源机制解和震源矩心深度，进而初步分析了本次地震的发震构造.结果显示，九寨沟M7.0地震的矩震级MW6.4，震源矩心深度5 km，表明主震发生在上地壳浅部，与2003年伊朗巴姆（Bam）MW6.5地震特征极为相似；12次ML ≥ 4.0级余震的震源矩心深度6~12 km，显示这些余震发生在主震下部，仅1次例外.重新定位后的余震震中呈NW-SE向窄带展布，位于近NS向的岷江断裂与近EW向的东昆仑断裂带东端分支塔藏断裂所夹持的区域，余震带长轴长约38 km，主震位于余震带中部.根据余震震中分布、主震及余震震源机制解等，推测本次九寨沟M7.0地震及其余震的主发震构造为位于岷江断裂与塔藏断裂之间的树正断裂.震源机制解揭示，树正断裂呈左旋走滑，走向约152°，近SE，倾向SW，倾角约70°，该断裂应属于东昆仑断裂东端的分支断裂之一，或与东南侧的虎牙断裂构成统一断裂系.
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| 关 键 词： | 九寨沟M7.0地震 重新定位 震源机制 发震构造 树正断裂 |
| 收稿时间： | 2017-08-30 |
Focal mechanism solutions and seismogenic structure of the 8 August 2017 M7.0 Jiuzhaigou earthquake and its aftershocks,northern Sichuan |
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| YI Gui-Xi,LONG Feng,LIANG Ming-Jian,ZHANG Hui-Ping,ZHAO Min,YE You-Qing,ZHANG Zhi-Wei,Qi Yu-Ping,WANG Si-Wei,GONG Yue,QIAO Hui-Zhen,WANG Zhi,QIU Gui-Lan,SU Jin-Rong.Focal mechanism solutions and seismogenic structure of the 8 August 2017 M7.0 Jiuzhaigou earthquake and its aftershocks,northern Sichuan[J].Chinese Journal of Geophysics,2017,60(10):4083-4097. |
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| Authors: | YI Gui-Xi LONG Feng LIANG Ming-Jian ZHANG Hui-Ping ZHAO Min YE You-Qing ZHANG Zhi-Wei Qi Yu-Ping WANG Si-Wei GONG Yue QIAO Hui-Zhen WANG Zhi QIU Gui-Lan SU Jin-Rong |
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| Institution: | 1. Sichuan Earthquake Agency, Chengdu 610041, China;
2. Sichuan Seistech Corporation Ltd., Chengdu 610041, China;
3. State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China |
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| Abstract: | On August 8, 2017, an M7.0 earthquake occurred in the Jiuzhaigou county of Sichuan Province at the eastern margin of the Tibetan Plateau, and the highest intensity is estimated up to Ⅸ, but no major surface ruptures have been observed in field survey, therefore, determination of seismogenic structures and assessment of associated seismic potential are still hampered. Based on the digital waveform data from Sichuan Regional Network, the M7.0 mainshock and its aftershocks were relocated by a multi-step locating method, and the focal mechanism solutions as well as the centroid depths of the M7.0 mainshock and its 13 ML ≥ 4.0 aftershocks were inverted simultaneously by the Cut and Paste (CAP) waveform inversion method. The seismogenic structure of the M7.0 Jiuzhaigou earthquake sequence will be analyzed and discussed.
The preliminary results indicate that the moment magnitude of the M7.0 Jiuzhaigou mainshock is MW6.4, and its centroid depth of 5 km means the occurrence of the mainshock at a shallow depth in the upper crust, which is very similar to the 2003 MW6.5 Bam earthquake in Iran. The centroid depths for 12 ML ≥ 4.0 aftershocks in the range of 6~12 km show that the aftershocks are deeper than the mainshock. The epicenters of the relocated aftershocks are distributed within a narrow zone along NW-SE direction, between the nearly NS-trending Minjiang fault zone and the Tazang fault zone, one of the splays of the EW-striking Eastern Kunlun fault zone. The NW-SE-trending long axis of the aftershock zone is about 38 km-long, and the M7.0 mainshock is located at the middle of the aftershock belt. Based on the spatial distribution of the relocated aftershocks, focal mechanism solutions, seismic intensity map and tectonic setting, we suggested that the M7.0 Jiuzhaigou mainshock and most aftershocks were generated on the Shuzheng fault between the Minjiang and Tazang faults. From the focal mechanism solutions of the Jiuzhaigou earthquake sequence, we infer that the Shuzheng fault is a SE-trending left-lateral strike-slip fault with dip of about 70° to southwest. This fault should be one of the branch faults of the eastern Kunlun fault zone, maybe connecting with the Huya fault to the southeast. |
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| Keywords: | M7 0 Jiuzhaigou earthquake Relocation Focal mechanism Seismogenic structure Shuzheng fault zone |
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