地震研究

使用亚失稳台阵和固定台站组成的密集台网观测资料,对2021年漾濞MS6.4地震前滇西北地区完备震级以上地震的频度、断层总面积和b值等地震活动性参数进行时空扫描分析,发现研究区4级以上地震失稳前均有较为明显的增频、增总面积、低b值等共性特征,漾濞MS6.4地震前以小震活动为指针的断层协同化演化进程大致可分为3个阶段:2020年5—12月为应变释放点产生阶段,小震频次缓慢增加; 2021年1月至5月17日为应变释放点扩展和增多阶段,小震频次逐步增多,3级以上地震释放点明显增强,且有向主震震中迁移现象,后期成带状扩展; 2021年5月18—21日为应变释放连接段,中小地震活动快速增长并最终连接成片,甚至重叠,且4级以上地震集中释放。而亚失稳过程则应是从2021年1月至5月17日为准静态阶段,2021年5月18—20日为准动态阶段。最后,讨论了出现明显的亚失稳过程的原因和断层协同演化进程划分存在的问题和不足。

In this paper,using the observation data of the dense network composed of meta-instability array and 10 fixed stations,we carry out the temporal and spatial scanning of seismic parameters such as frequency,total fault area,and b-value of the complete magnitude before the Yangbi MS6.4 earthquake in northwest Yunnan province.We find that there are obvious common characteristics such as increasing frequency,increasing total fault area and low b-value before the instability of the M>4.0 earthquakes in the study area.The coordinated evolution of faults with small-earthquake activity as the indication before the Yangbi MS6.4 earthquake can be roughly divided into three stages:①the period from May to December 2020,in which strain-release points appeared,and the frequency of small earthquakes increased slowly; ②the period from January to May 17,2021,in which the strain-release points increased and extended,and the frequency of small earthquakes increased,and the number of M>3.0 earthquakes increased significantly,and their epicenters migrated to the epicenter of the main earthquake.At the end of the stage,the strain-release points expanded into a belt.③the period from May 18 to 21,2021,in which the strain-release points linked together and even overlapped.And small and medium earthquakes increased rapidly,and the M>4.0 earthquakes concentrated.We conclude that the meta-instability process should consist of the static phase(from January to May 17,2021),and the dynamic phase(from May 18 to 20,2021).Finally we discuss the causes of the meta-instability and the questions in the division of the meta-instability process.

引言
1 数据来源及记录
2 漾濞M_S6.4地震前亚失稳过程地震活动性响应特征
3 漾濞M_S6.4地震亚失稳过程分析
4 结论与讨论

图1 滇西北亚失稳密集台站与ML≥4.0地震空间分布(2018-04—2021-05)<br/>Fig.1 Distribution of the observation stations and ML≥4.0 earthquakes in northwest Yunnan (2018-04—2021-05)

图1 滇西北亚失稳密集台站与ML≥4.0地震空间分布(2018-04—2021-05)
Fig.1 Distribution of the observation stations and ML≥4.0 earthquakes in northwest Yunnan (2018-04—2021-05)

图2 研究区震级-频度关系<br/>Fig.2 Magnitude-frequency relationship and the complete magnitude in the study area

图2 研究区震级-频度关系
Fig.2 Magnitude-frequency relationship and the complete magnitude in the study area

图3 2018年以来研究区ML≥3.0地震时空迁移图<br/>Fig.3 Spatial and temporal migration of ML≥3.0 earthquakes in the study area

图3 2018年以来研究区ML≥3.0地震时空迁移图
Fig.3 Spatial and temporal migration of ML≥3.0 earthquakes in the study area

表1 2018年以来滇西北地区4次中强地震参数<br/>Tab.1 Parameters of four moderate-strong earthquakes in northwest Yunnan since 2018

表1 2018年以来滇西北地区4次中强地震参数
Tab.1 Parameters of four moderate-strong earthquakes in northwest Yunnan since 2018

图4 2018年以来研究区ML≥2.0地震频度(步长15 d,窗长60 d)<br/>Fig.4 Frequency diagram of ML≥2.0 earthquakes in the study area since 2018(Step=15 days,window=60 days)

图4 2018年以来研究区ML≥2.0地震频度(步长15 d,窗长60 d)
Fig.4 Frequency diagram of ML≥2.0 earthquakes in the study area since 2018(Step=15 days,window=60 days)

图5 2018年以来研究区ML0.8～3.5地震滑动断层总面积曲线(步长15 d,窗长60 d)<br/>Fig.5 A(t)curve of the ML0.8～3.5 earthquakes in the study area since 2018(step=15 days,window=60 days)

图5 2018年以来研究区ML0.8～3.5地震滑动断层总面积曲线(步长15 d,窗长60 d)
Fig.5 A(t)curve of the ML0.8～3.5 earthquakes in the study area since 2018(step=15 days,window=60 days)

图6 2018年以来研究区ML0.8～3.5地震滑动b值(步长15 d,窗长60 d)<br/>Fig.6 b-values of ML0.8～3.5 earthquakes in the study area since 2018(step=15 days,window=60 days)

图6 2018年以来研究区ML0.8～3.5地震滑动b值(步长15 d,窗长60 d)
Fig.6 b-values of ML0.8～3.5 earthquakes in the study area since 2018(step=15 days,window=60 days)

表2 2018年以来研究区低b值时段与ML≥4.0失稳地震事件<br/>Tab.2 Periods of low b values and seismic events of ML≥4.0 in the study area since 2018

表2 2018年以来研究区低b值时段与ML≥4.0失稳地震事件
Tab.2 Periods of low b values and seismic events of ML≥4.0 in the study area since 2018

图7 断层失稳过程的剪应力-时间曲线(据马瑾等,1995,2012)<br/>Fig.7 Shear stress-time curve of fault instability process(based on Ma et al,1995,2012)

图7 断层失稳过程的剪应力-时间曲线(据马瑾等,1995,2012)
Fig.7 Shear stress-time curve of fault instability process(based on Ma et al,1995,2012)

图8 漾濞MS6.4主震前3 d地震M-T图<br/>Fig.8 M-T diagram of the earthquakes 3 days before the Yangbi MS6.4 earthquake

图8 漾濞MS6.4主震前3 d地震M-T图
Fig.8 M-T diagram of the earthquakes 3 days before the Yangbi MS6.4 earthquake

图9 MS4.2和MS4.4前震序列时空展布和快速连接情况<br/>Fig.9 Temporal and spatial distribution and connection of the MS4.2 and the MS4.4 earthquake sequence

图9 MS4.2和MS4.4前震序列时空展布和快速连接情况
Fig.9 Temporal and spatial distribution and connection of the MS4.2 and the MS4.4 earthquake sequence

表3 漾濞主震前3 d内M≥3.0地震震源机制解<br/>Tab.3 Focal mechanism solutions of the M≥3.0 earthquakes 3 days before the main shock

表3 漾濞主震前3 d内M≥3.0地震震源机制解
Tab.3 Focal mechanism solutions of the M≥3.0 earthquakes 3 days before the main shock

图10 前震序列P轴(a)和T轴(b)优势方向<br/>Fig.10 The dominant direction of the P-axis(a)and T-axis(b)of the foreshock sequence

图10 前震序列P轴(a)和T轴(b)优势方向
Fig.10 The dominant direction of the P-axis(a)and T-axis(b)of the foreshock sequence

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备注

引言

1 数据来源及记录

2 漾濞M_S6.4地震前亚失稳过程地震活动性响应特征

3 漾濞M_S6.4地震亚失稳过程分析

4 结论与讨论

期刊信息

备注

引言

1 数据来源及记录

2 漾濞MS6.4地震前亚失稳过程地震活动性响应特征

3 漾濞MS6.4地震亚失稳过程分析

4 结论与讨论

期刊信息

2 漾濞M_S6.4地震前亚失稳过程地震活动性响应特征

3 漾濞M_S6.4地震亚失稳过程分析