王月^1,,
胡少乾²,
何骁慧^3,4,,,
郭凯¹,
解孟雨¹,
邓世广¹,
马亚伟¹
1. 中国地震台网中心, 北京 100045
2. 中国地质大学(武汉), 地球物理与空间信息学院, 地球内部多尺度成像湖北省重点实验室, 武汉 430074
3. 中山大学地球科学与工程学院, 广东省地球动力作用与地质灾害重点实验室, 广州 510275
4. 南方海洋科学与工程广东省实验室(珠海), 珠海 519082

基金项目: 国家重点研发（2018YFC150330502），中国地震局监测预报司震情跟踪定向工作任务（2021010126）和中山大学中央高校基本科研业务费专项资金（2021qntd23）共同资助


详细信息

作者简介: 王月, 博士, 高级工程师, 主要从事地震精定位及结构反演等方面的研究.E-mail: wangyue@seis.ac.cn

通讯作者: 何骁慧, 博士, 副教授, 主要从事地震震源研究.E-mail: hexiaoh5@mail.sysu.edu.cn

中图分类号: P315

收稿日期:2021-06-10
修回日期:2021-08-26
上线日期:2021-12-10

Relocation and focal mechanism solutions of the 21 May 2021 M_S6.4 Yunnan Yangbi earthquake sequence

WANG Yue^1,,
HU ShaoQian²,
HE XiaoHui^3,4,,,
GUO Kai¹,
XIE MengYu¹,
DENG ShiGuang¹,
MA YaWei¹
1. China Earthquake Networks Center, Beijing 100045, China
2. Hubei Subsurface Multi-scale Imaging Laboratory, Institute of Geophysics and Geomatics, China University of Geosciences, Wuhan 430074, China
3. Guangdong Provincial Key Laboratory of Geodynamics and Geohazards, School of Earth Sciences and Engineering, Sun Yat-sen University, Guangzhou 510275, China
4. Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai), Zhuhai 519082, China


More Information

Corresponding author: HE XiaoHui,E-mail:hexiaoh5@mail.sysu.edu.cn

MSC: P315

--> Received Date: 10 June 2021
Revised Date: 26 August 2021
Available Online: 10 December 2021


摘要
摘要:2021年5月21日21时，云南省大理州漾濞县先后发生M_S5.6和M_S6.4地震，两次地震震中位置相距约7 km，均位于滇西地区，该地区地处青藏高原东南缘、南北地震带南段，地质构造复杂.地震序列跟踪结果显示漾濞M_S6.4地震类型为前震-主震-余震型，M_S5.6地震为M_S6.4地震的前震.本文基于云南地震台网的震相报告，采用双差定位方法对漾濞M_S6.4地震早期序列（2021年5月18日至25日，M_L0.0以上）进行重定位，同时，利用Cut-And-Paste（CAP）震源机制波形反演方法，获得了序列中截止至5月25日31次M_S ≥ 3.0地震的震源机制解和矩心深度，对该序列的发震构造进行了初步分析.结果显示：（1）重定位后获得的2159个地震事件呈NW-SE向展布，长约25 km，宽约5~10 km.M_S6.4主震的震源深度为8.9 km，序列震源深度主要集中在4~10 km，深度均值约7.5 km.（2）前震序列具有从中间开始破裂，然后向北西向破裂，继而向东南向破裂的特征，漾濞M_S6.4主震位于余震区的北西端，最大余震M_S5.2地震位于余震区的东南端.（3）CAP波形反演获得的31次M_S ≥ 3.0地震的震源矩心深度在4~11 km范围，深度均值约6.5 km，与重定位结果接近，仅相差1.0 km，说明重定位的震源深度分布是合理可靠的.（4）震源机制多为右旋走滑型，部分地震具有较为明显的正断分量，反演的区域应力场与目前已知的构造应力场水平主压应力方向一致，反映区域内构造活动主要受区域构造应力场控制.根据重定位后的序列空间分布、震源机制解及震源区构造特征，综合分析认为，此次漾濞地震序列的发震构造可能是维西-乔后-巍山断裂中段附近的次级断层.
关键词: 漾濞M_S6.4地震/
重定位/
震源机制/
发震构造

Abstract:On May 21, 2021, two earthquakes, with magnitudes of 5.6 and 6.4 respectively, struck the Yangbi County in Yunnan, China. The epicenters of the two earthquakes were about 7 km apart, and both were located in the western Yunnan region. This region is located in the southeastern margin of the Qinghai-Tibet Plateau and the southern segment of the north-south seismic belt. Preliminary analysis shows the Yangbi M_S6.4 earthquake sequence is with foreshock-mainshock-aftershock type, and the M_S5.6 earthquake is the foreshock of the M_S6.4 earthquake. In this study, using the seismic phase report provided by Yunnan Earthquake Networks, we relocated the early events (with local magnitude M_L larger than 0.0 from May 18 to 25, 2021) of the M_S6.4 Yangbi earthquake sequence using the double-difference relocation method. Meanwhile, the focal mechanism solutions and centroid depths of 31 M_S ≥ 3.0 events in the sequence were determined using the Cut-And-Paste (CAP) waveform inversion method. The seismogenic structure of the earthquake sequence based on the inverted results is also discussed. The results indicate: (1) The relocated 2159 M_L ≥ 0.0 events are distributed in a narrow zone with a length of ~25 km in the NW-SE direction, and a width of 5~10 km. The focal depth of the main shock is 8.9 km, and the depth range of the sequence is between 4 and 10 km with an average depth of 7.5 km. (2) The foreshock sequence shows the rupture starts from the middle, then goes to NW and finally to the SE direction. The epicenter of the main shock is located in the NW end of the aftershock region, and the epicenter of the largest aftershock (M_S5.2 earthquake) is located in the SE end of the region. (3) The centroid depths of all the 31 events with M_S ≥ 3.0 from CAP method range from 4 to 11 km with a mean value of around 6.5 km, which is consistent with the predominant focal depth of the whole sequence from double-difference method. The agreement of the results of the two methods verify that the double-difference relocation result is reliable. (4) The focal mechanism solutions of the 31 M_S ≥ 3.0 events are mostly of strike-slip type, while some events show an obvious normal-fault component. The inverted stress result based on the focal mechanism solution is consistent with the regional horizontal principal compressional stress field, which indicates that the tectonic activity in this region is mainly controlled by the regional tectonic stress field. According to the distribution of relocated earthquake sequence, combined with the focal mechanism solutions and the regional structures, we conclude that the seismogenic structure for the Yangbi M_S6.4 earthquake sequence is a secondary fault of the Weixi-Qiaohou-Weishan fault system.
Key words:Yangbi M_S6.4 earthquake/
Relocation/
Focal mechanism/
Seismogenic structure



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