地震研究

2023年云南芒市M_L4.0震群序列研究

(1.云南省地震局,云南昆明 650224; 2.中国地震局昆明地震预报研究所,云南昆明 650224)

Research on the Characteristics of the Mangshi M_L4.0 Earthquake Sequence in 2023

YANG Yuncun¹,JIANG Jinzhong^1,2,LIU Kexiang¹,WANG Hualiu¹,SUN Zigang¹,YANG Mingchang¹

(1.Yunnan Earthquake Agency,Kunming 650224,Yunnan,China；2.Kunming Institute of Prediction,China Earthquake Administration,Kunming 650224,Yunnan,China)

Keywords：the Mangshi earthquake swarm; double difference positioning; CAP inversion; earthquake activity; fluid diffusion

DOI: 10.20015/j.cnki.ISSN1000-0666.2025.0002

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参考文献

基于云南地震台网和腾冲火山台网的宽频带地震波形资料和震相报告文件以及川滇地区高分辨率公共速度模型2.0版,采用结合波形互相关技术的双差相对定位法对2023年云南芒市M_L4.0震群序列中442次地震进行重定位,利用CAP方法反演了地震序列中M_L≥3.5地震震源机制解,研究了芒市M_L4.0震群序列的发震机理,探讨该震群是前震序列还是普通震群。双差定位法获得了363次地震的精定位结果,震中走向呈NE向,地震序列呈三角形形态分布。CAP波形反演M_L4.0地震最佳双力偶机制解为节面I走向45°,倾角70°,滑动角-61°; 节面II走向167°,倾角35°,滑动角-143°,矩震级为M_W3.91,最佳矩心深度为7 km。综合精定位后地震序列的时空分布特征、震源机制解信息、S-P走时差、区域地质构造和地震活动性探讨此次地震的发震构造及孕震环境,结果表明:此次震群不是前震序列,而是一次普通的3～4级震群活动。地震序列在不同阶段的时空演化过程可能是由至少2条存在一定夹角的断层结构在高应力和区域的温泉地热活动引发。

Based on the broadband seismic waveform data and seismic phase reports produced by the Yunnan Seismic Network and the Tengchong Volcano Network,as well as the latest developed high-resolution common velocity model(Version 2.0)of the Crust in Sichuan-Yunnan region,the double-difference relative positioning method combined with waveform cross-correlation techniques is used to relocate 442 earthquakes in the Mangshi,Yunnan M_L4.0 earthquake sequence in 2023.The CAP method is used to invert the focal mechanism solution of the M_L≥3.5 earthquakes in the sequence,and the seismogenic mechanism of the sequence is studied in depth to explore whether this sequence is a foreshock sequence or just an ordinary earthquake swarm.Through the double-difference location method,precise locations of 363 earthquakes are obtained.Their epicenters are distributed in NE direction,and these earthquakes are distributed in a triangular shape.The optimal double-couple mechanism solution of the main shock,the M_L4.0 earthquake,is obtained through CAP waveform inversion:the nodal Plane I strikes 45 °,the dip angle is 70 °,and the sliding angle is -61 °.The nodal Plane II has a strike of 167 °,an inclination of 35 °,a slip angle of -143 °,a moment magnitude(M_W)of 3.91,and an optimal depth of 7 km.The temporal and spatial distribution characteristics of this earthquake sequence,the focal mechanism solution information,the travel time difference(S-P),the regional geological structure and the earthquake activity through the comprehensive precise positioning are used to explore the seismogenic structure and the seismogenic environment of this earthquake swarm.The results show that this earthquake swarm is not a foreshock sequence,but an ordinary earthquake swarm(magnitudes between 3 to 4).This earthquake sequence occurred on at least two faults.The faults are in high stress state and form an angle.The underground fluid affected this earthquake sequence's evolution at different stages.

引言
1 数据选取
2 研究结果
3 讨论
4 结论

图1 2023年芒市ML4.0震群地震序列空间分布、断裂、周边台站和历史强震分布图<br/>Fig.1 The 2023 Mangshi ML4.0 earthquake swarm,faults,stations,and historical strong earthquakes in the study area

图1 2023年芒市ML4.0震群地震序列空间分布、断裂、周边台站和历史强震分布图
Fig.1 The 2023 Mangshi ML4.0 earthquake swarm,faults,stations,and historical strong earthquakes in the study area

图2 2023年芒市ML4.0震群地震序列M-T(a)和ΔT-T(b)图<br/>Fig.2 The M-T(a)and ΔT-T(b)diagrams of the 2023 Mangshi ML4.0 earthquake swarm

图2 2023年芒市ML4.0震群地震序列M-T(a)和ΔT-T(b)图
Fig.2 The M-T(a)and ΔT-T(b)diagrams of the 2023 Mangshi ML4.0 earthquake swarm

表1 云南地震台网记录的2023年芒市ML4.0震群ML≥3.0地震目录<br/>Tab.1 ML≥ 3.0 earthquakes in the 2023 Mangshi ML4.0 earthquake swarm recorded by the Yunnan Seismic Network

表1 云南地震台网记录的2023年芒市ML4.0震群ML≥3.0地震目录
Tab.1 ML≥ 3.0 earthquakes in the 2023 Mangshi ML4.0 earthquake swarm recorded by the Yunnan Seismic Network

图3 用于CAP反演的P波(实线)、S波(虚线)速度模型(a)和震相观测走时曲线(b)<br/>Fig.3 P-wave velocity model(solid line),S-wave velocity model(dashed line)(a),and the travel-time curves of the observed seismic phases(b)for CAP inversion

图3 用于CAP反演的P波(实线)、S波(虚线)速度模型(a)和震相观测走时曲线(b)
Fig.3 P-wave velocity model(solid line),S-wave velocity model(dashed line)(a),and the travel-time curves of the observed seismic phases(b)for CAP inversion

表2 利用CAP方法反演2023年芒市ML4.0震群ML≥3.5地震的震源机制解和最佳矩心深度<br/>Tab.2 The source mechanism solution and the optimal moment center depth of the ML≥3.5 earthquakes in the 2023 Mangshi ML4.0 earthquake swarm inverted by the CAP method

表2 利用CAP方法反演2023年芒市ML4.0震群ML≥3.5地震的震源机制解和最佳矩心深度
Tab.2 The source mechanism solution and the optimal moment center depth of the ML≥3.5 earthquakes in the 2023 Mangshi ML4.0 earthquake swarm inverted by the CAP method

图4 基于区域速度模型A(a)和模型B(b)的ML4.0主震CAP方法震源深度拟合结果<br/>Fig.4 Fitted results of the waveform of the ML4.0 earthquake with CAP method based on regional velocity model A(a)and model B(b)

图4 基于区域速度模型A(a)和模型B(b)的ML4.0主震CAP方法震源深度拟合结果
Fig.4 Fitted results of the waveform of the ML4.0 earthquake with CAP method based on regional velocity model A(a)and model B(b)

图5 基于区域速度模型A(a)和模型B(b)的ML4.0主震CAP方法波形拟合结果<br/>Fig.5 Waveform fitting results of ML4.0 earthquake with CAP method based on regional velocity model A(a)and model B(b)

图5 基于区域速度模型A(a)和模型B(b)的ML4.0主震CAP方法波形拟合结果
Fig.5 Waveform fitting results of ML4.0 earthquake with CAP method based on regional velocity model A(a)and model B(b)

图6 2023年芒市ML4.0震群的时空演化图(a)和AA'剖面投影(b)
Fig.6 Spatiotemporal evolution of the Mangshi ML4.0 earthquake swarm(a)and AA' profile projection(b)

图7 芒市台(MAS)记录的6个阶段S和P震相到时差<br/>Fig.7 The arrival-time differences between the phases S-phase and P-phase in 6 stages recorded by Mangshi station

图7 芒市台(MAS)记录的6个阶段S和P震相到时差
Fig.7 The arrival-time differences between the phases S-phase and P-phase in 6 stages recorded by Mangshi station

图8 6个阶段ML≥3.4地震时空演化(a～f)和重定位之后震源深度随时间的变化(g)<br/>Fig.8 The spatiotemporal evolution of ML≥3.4 earthquakes(a-f)and the variation of source depth with time after relocation(g)

图8 6个阶段ML≥3.4地震时空演化(a～f)和重定位之后震源深度随时间的变化(g)
Fig.8 The spatiotemporal evolution of ML≥3.4 earthquakes(a-f)and the variation of source depth with time after relocation(g)