地震研究

2013年以来,维西—乔后断裂带进入中强地震活跃期,2021年5月21日漾濞MS6.4地震发生前,已有3组MS≥5.0地震连续发生,表明该断裂带地震活动显著增强。采用双差定位方法对2013年以来发生在维西—乔后断裂带周边的4组地震序列进行重定位,并使用ZMAP软件包计算序列的b值和p值。结果显示,维西—乔后断裂带周边地震序列呈现出两组明显不同的时空分布特征,余震序列优势分布方向为NW向的3组地震序列衰减较快,序列b值相对较低,序列震中分布长宽比较大; 2016年云龙MS5.0地震序列优势分布方向为NE向,序列震中分布长宽比较小,衰减较慢,序列b值相对较高。基于序列类比结果和b值时间变化曲线分析认为,2021年漾濞MS6.4地震序列后续发生较大破坏性余震的可能性较小。综合2013年以来维西—乔后断裂带中强地震时空分布特征和区域地质构造资料分析认为,未来该地区MS≥5.0地震存在向东南或向北迁移的可能性。

Before the Yangbi MS6.4 earthquake on May 21,2021,three groups of MS≥5.0 earthquakes have occurred continuously,indicating that the seismic activity of the Weixi-Qiaohou fault zone has increased significantly since 2013.In this paper,we employ double-difference relocation algorithm to relocate earthquake sequences around the Weixi-Qiaohou fault zone since 2013,and use ZMAP to calculate the b-value and p-value of these sequences.The earthquake sequences around the Weixi-Qiaohou fault zone present obviously two different types of temporal-spatial distribution characteristics.Three earthquake sequences concentrate in a NW-trend band,which is parallel with the Weixi-Qiaohou fault,and the length-width ratios of the epicenter distribution of these earthquake sequences are larger.Furthermore,these three earthquake sequences decay faster and their b-values are relatively lower,while the Yunlong MS5.0 earthquake sequence in 2016 concentrates to a NE-trend band,and the length-width ratio of the epicenter distribution is relatively smaller.Also,the Yunlong MS5.0 earthquake sequence decays slower than the other three earthquake sequences,and its b-value is relatively higher.A contrastive analysis of earthquake sequences around the Weixi-Qiaohou fault zone shows that the possibility of large destructive aftershocks following the 2021 Yangbi MS6.4 earthquake sequence is small.Based on a comprehensive analysis of the spatial-temporal distribution characteristics of the moderately-strong earthquakes in the Weixi Qiaohou fault zone since 2013 and regional geological structure study,it is considered that MS≥5.0 earthquakes in this area may migrate to the Southeast(or the North)in the future.

引言
1 数据与方法
2 结果分析
3 讨论
4 结论

图1 漾濞地震周边断裂、历史地震和测震台站分布<br/>Fig.1 Faults,historical earthquakes and seismic stations around the Yangbi earthquake

图1 漾濞地震周边断裂、历史地震和测震台站分布
Fig.1 Faults,historical earthquakes and seismic stations around the Yangbi earthquake

图2 维西—乔后断裂带地震序列M-T图<br/>Fig.2 Magnitude-time distribution of earthquake sequences in the Weixi-Qiaohou fault zone

图2 维西—乔后断裂带地震序列M-T图
Fig.2 Magnitude-time distribution of earthquake sequences in the Weixi-Qiaohou fault zone

图3 维西—乔后断裂带地震序列震级-频度分布<br/>Fig.3 Magnitude-Frequency distribution of earthquake sequences in the Weixi-Qiaohou fault zone

图3 维西—乔后断裂带地震序列震级-频度分布
Fig.3 Magnitude-Frequency distribution of earthquake sequences in the Weixi-Qiaohou fault zone

图4 维西—乔后断裂带地震序列余震频度随时间衰减结果<br/>Fig.4 Temporal decay of aftershocks with modified Omori's law of earthquake sequences in the Weixi-Qiaohou fault zone

图4 维西—乔后断裂带地震序列余震频度随时间衰减结果
Fig.4 Temporal decay of aftershocks with modified Omori's law of earthquake sequences in the Weixi-Qiaohou fault zone

图5 2013年洱源MS5.5地震序列震中分布(a)、沿AA深度剖面(b)和BB深度剖面(c)
Fig.5 Spatial distribution(a),AA depth profile(b),and BB depth profile(c) of the 2013 Eryuan MS5.5 earthquake sequence

图6 2013年洱源MS5.0地震序列震中分布(a)、沿AA深度剖面(b)和BB深度剖面(c)
Fig.6 Spatial distribution(a),AA depth profile(b),and BB depth profile(c) of the 2013 Eryuan MS5.0 earthquake sequence

图7 2016年云龙MS5.0地震序列震中分布(a)、沿AA深度剖面(b)和BB深度剖面(c)
Fig.7 Spatial distribution(a),AA depth profile(b),and BB depth profile(c)of the 2016 Yunlong MS5.0 earthquake sequence

图8 2017年漾濞MS5.1地震序列震中分布(a)、沿AA深度剖面(b)和BB深度剖面(c)
Fig.8 Spatial distribution(a),AA depth profile(b),and BB depth profile(c)of the 2017 Yangbi MS5.1 earthquake sequence

图9 2021年漾濞MS6.4地震序列震中分布(a)、沿AA深度剖面(b)和BB深度剖面(c)
Fig.9 Spatial distribution(a),AA depth profile(b),and BB depth profile(c)of the 2021 Yangbi MS6.4 earthquake sequence

表1 维西—乔后断裂地震序列时空分布特征<br/>Tab.1 Characteristics of temporal-spatial distribution of earthquake sequences located in the Weixi-Qiaohou fault zone

表1 维西—乔后断裂地震序列时空分布特征
Tab.1 Characteristics of temporal-spatial distribution of earthquake sequences located in the Weixi-Qiaohou fault zone

图10 2020-07-01至2021-06-30(a)和2021-05-15至2021-06-22(b)漾濞MS6.4地震震源区b值随时间变化曲线<br/>Fig.10 b-value time curve of the Yangbi MS6.4 focal area from July 1,2020 to June 30,2021(a)and from May 15,2021 to June 22,2021(b)

图10 2020-07-01至2021-06-30(a)和2021-05-15至2021-06-22(b)漾濞MS6.4地震震源区b值随时间变化曲线
Fig.10 b-value time curve of the Yangbi MS6.4 focal area from July 1,2020 to June 30,2021(a)and from May 15,2021 to June 22,2021(b)

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备注

引言

1 数据与方法

2 结果分析

3 讨论

4 结论

期刊信息