地震研究

2022年四川马尔康6.0级震群序列震源机制特征分析

王莹,金昭娣,赵韬

(陕西省地震局,陕西西安 710068)

The Characteristics of the Focal Mechanisms of the Ma'erkang M_S6.0 Earthquake Sequence in 2022

WANG Ying,JIN Zhaodi,ZHAO Tao

(Shaanxi Earthquake Agency,Xi'an 710068,Shaanxi,China)

Keywords：the Ma'erkang M_S6.0 earthquake swarm; focal mechanism solution; moment tensor inversion; earthquake seqnence; seismogenic structure

DOI: 10.20015/j.cnki.ISSN1000-0666.2024.0035

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采用近震全波形矩张量方法反演了2022年四川马尔康6.0级震群序列22次地震的震源机制解,结果显示:这22次地震全部为走滑型,断层面走向呈NNW和NE两个优势方向,断层面倾角近似直立,滑动角分布在0°和180°附近,P轴优势方位为NWW-SEE向,倾伏角接近水平,表明此次地震事件主要受区域NWW-SEE向水平挤压应力场控制。3次5级以上地震震源机制均与序列其他地震的总体震源机制差异较小,说明序列震源机制较为一致。结合精定位结果综合分析认为:马尔康震群属于多断层面触发性震群,3次5级以上地震是不同断裂的破裂事件,其中5.8级和6.0级地震发震断层面走向为NNW,为左旋走滑破裂事件; 5.2级地震发震断层面走向为NE,为右旋走滑破裂事件,3个发震断层均以走滑错动为主,断层面近似直立。

In this paper,the focal mechanism solutions of 22 events of the Ma'erkang M_S6.0 earthquake sequence were obtained with the method of full-waveform moment tensor inversion.The results show that these 22 earthquakes are strike-slip ones,and the trend of their fault plane is mainly in NNW direction and NE direction.The dip angle of the fault plane is approximately vertical,and the slip angle is close to 0° or 180°.The azimuth of the P-axis is in NWW-SEE direction,and the plunge angle is close to horizontal.This indicates that the activity of the Ma'erkang M_S6.0 earthquake sequence is mainly compressed in NWW-SEE direction by the regional horizontal stress field.The focal mechanisms of the three M_S≥5.0 earthquakes are slightly different from the focal mechanisms of other earthquakes in the sequence.According to the results of precise location,we believe that the Ma'erkang M_S6.0 earthquake sequence is triggered by multiple planes.The three M_S≥5.0 earthquakes were caused by different faults.The strike of the fault planes of the M_S5.8 and the M_S6.0 earthquake are in NNW direction; the rupture of the planes is right-lateral and strike-slip.The strike of the fault plane of the M_S5.2 earthquake is in NE direction; its rupture is left-lateral and strike-slip.The fault planes of the three earthquakes are approximately vertical.

引言
1 方法与数据
2 地震序列震源机制解结果
3 地震序列震源机制解特征分析
4 讨论
5 结论

图1 马尔康6.0级震群附近构造分布及22次震源机制结果<br/>Fig.1 Structures and 22 focal mechanisms in the vicinity of the Ma'erkang MS6.0 earthquake swarm

图1 马尔康6.0级震群附近构造分布及22次震源机制结果
Fig.1 Structures and 22 focal mechanisms in the vicinity of the Ma'erkang MS6.0 earthquake swarm

表1 本文计算的马尔康6.0级震群序列中22次地震事件的震源机制解<br/>Tab.1 The focal mechanism solutions of 22 earthquakes of the Ma'erkang MS6.0 earthquake swarm

表1 本文计算的马尔康6.0级震群序列中22次地震事件的震源机制解
Tab.1 The focal mechanism solutions of 22 earthquakes of the Ma'erkang MS6.0 earthquake swarm

图2 2022年6月10日00:03分马尔康5.8级地震最佳深度处波形拟合图(a)、震源机制深度误差图(b)和反演结果(c)<br/>Fig.2 Waveform fitting at the optimal depth(a),error of the focal mechanism depth(b),and the inverted focal mechanism(c)of the Ma'erkang MS5.8 earthquake at 00:03 on June 10,2022

图2 2022年6月10日00:03分马尔康5.8级地震最佳深度处波形拟合图(a)、震源机制深度误差图(b)和反演结果(c)
Fig.2 Waveform fitting at the optimal depth(a),error of the focal mechanism depth(b),and the inverted focal mechanism(c)of the Ma'erkang MS5.8 earthquake at 00:03 on June 10,2022

图3 2022年6月10日01:28分马尔康6.0级地震最佳深度处波形拟合图(a)、震源机制深度误差图(b)和反演结果(c)<br/>Fig.3 Waveform fitting at the optimal depth(a),error of the focal mechanism depth(b),and the inverted focal mechanism(c)of the Ma'erkang MS6.0 earthquake at 01:28 on June 10,2022

图3 2022年6月10日01:28分马尔康6.0级地震最佳深度处波形拟合图(a)、震源机制深度误差图(b)和反演结果(c)
Fig.3 Waveform fitting at the optimal depth(a),error of the focal mechanism depth(b),and the inverted focal mechanism(c)of the Ma'erkang MS6.0 earthquake at 01:28 on June 10,2022

图4 2022年6月10日03:27分马尔康5.2级地震最佳深度处波形拟合图(a)、震源机制深度误差图(b)和反演结果(c)<br/>Fig.4 Waveform fitting at the optimal depth(a),error of the focal mechanism depth(b),and the inverted focal mechanism(c)of the Ma'erkang MS5.2 earthquake at 03:27 on June 10,2022

图4 2022年6月10日03:27分马尔康5.2级地震最佳深度处波形拟合图(a)、震源机制深度误差图(b)和反演结果(c)
Fig.4 Waveform fitting at the optimal depth(a),error of the focal mechanism depth(b),and the inverted focal mechanism(c)of the Ma'erkang MS5.2 earthquake at 03:27 on June 10,2022

图5 马尔康6.0级震群序列震源机制分类<br/>Fig.5 Focal mechanism classification of the Maerkang MS6.0 earthquake swarm

图5 马尔康6.0级震群序列震源机制分类
Fig.5 Focal mechanism classification of the Maerkang MS6.0 earthquake swarm

表2 3次5级以上地震以外其他地震事件总体震源机制特征<br/>Tab.2 Overall characteristics of the focal mechanisms of the seismic events excluding three MS≥5.0 earthquakes

表2 3次5级以上地震以外其他地震事件总体震源机制特征
Tab.2 Overall characteristics of the focal mechanisms of the seismic events excluding three MS≥5.0 earthquakes

图6 3次5级以上地震震源机制(a)和其对应的其他地震事件总体震源机制特征分析(b)<br/>Fig.6 Characteristic analysis of focal mechanism of three MS≥5.0 earthquakes(a)and the overall focal mechanism of other seismic events(b)

图6 3次5级以上地震震源机制(a)和其对应的其他地震事件总体震源机制特征分析(b)
Fig.6 Characteristic analysis of focal mechanism of three MS≥5.0 earthquakes(a)and the overall focal mechanism of other seismic events(b)

图7 马尔康6.0级震群序列震源机制解节面走向(a)、滑动角(b)、倾角(c)与P、T轴方位角、倾伏角统计(d～g)<br/>Fig.7 Statistics of strike(a),rake(b),dip(c),azimuth and plunge of P-axis and T-axis(d～g ) of the MS≥6.0 earthquake swarm

图7 马尔康6.0级震群序列震源机制解节面走向(a)、滑动角(b)、倾角(c)与P、T轴方位角、倾伏角统计(d～g)
Fig.7 Statistics of strike(a),rake(b),dip(c),azimuth and plunge of P-axis and T-axis(d～g ) of the MS≥6.0 earthquake swarm