基于机器学习和短周期密集台阵资料研究北流地震余震特征|gnss公司厦门海川润泽地灾普适型_泥石流

基于机器学习和短周期密集台阵资料研究北流地震余震特征

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

南方海洋科学与工程广东省实验室(珠海), 广东珠海 519082

国家自然基金项目（41874052和41730212），广东省引进人才创业创新团队（2016ZT06N331和2017ZT07Z066），国家重点研发计划（2017YFC1500103），广东省防震减灾协同创新中心（2018B020207011），和第二次青藏高原综合科学考察研究（2019QZKK0701）联合资助

中图分类号:P315

Guangdong Provincial Key Lab of Geodynamics and Geohazards, School of Earth Sciences and Engineering, Sun Yat-Sen University, Guangzhou 510275, China

Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai Guangdong 519082, China

本文基于广西北流5.2级地震震源区震后约30天的短周期密集台阵连续观测资料，利用机器学习方法，对震后余震进行了识别，确定了可靠性较高的441个余震事件，约为同时期固定地震台网目录中余震数量的34倍.进而利用事件波形中P、S波到时信息，对299个余震事件进行了精定位，对信噪比较高的65个地震事件进行了震源机制解反演.根据余震空间分布及震源机制解特征，对该区域中强地震发震构造进行了探讨.结果表明：北流地震的余震主要集中在主震北西约1~3 km的范围内，且大部分余震震源机制解接近于前震；主震的孕震断裂为石窝断层，其走向NWW-SEE，倾角近70°；该区域还存在一条走向NEE-SWW倾角近乎直立的断裂，可能是前震的孕震断层；主震受前震的触发而产生，而后续两条断裂同时处于活动状态，产生了不同震源机制解的余震.此外，在蕉林断裂北端及石窝断裂南端同样拾取到了大量余震事件，这些事件的震源机制解多为逆冲型与走滑型，一致性较差，表明北流地震可能对这两个区域的地震活动起了一个触发作用，但具体触发机制较为复杂.

In this study, a machine learning method is used to detect the aftershocks of the Guangxi Beiliu 5.2 earthquake based on the 30 days continuous records of dense nodal seismic array. 441 reliable events are detected, which is around 34 times the number from permanent seismic network in the same period. P and S wave arrival time information is used to obtain an earthquake catalog with 299 events. In addition, the focal mechanism solutions of 65 aftershocks with high SNR waveforms are acquired by using the gCAP method. The seismogenic structure of strong earthquakes in this region is discussed based on the spatial distribution of aftershocks and focal mechanism solution characteristics. The results show that the aftershocks of the Beiliu earthquake are mainly concentrated in a range of about 1~3 km northwest of the main shock, and the focal mechanism solutions mostly are closed to the foreshock. The seismogenic fault of the mainshock is the Shiwo fault with a strike of NWW-SEE and a dip angle of nearly 70°. In addition, we speculate that there is a NEE-SWW fault in this region, which may be the seismogenic fault of the foreshock. The mainshock is triggered by the foreshock, and then the two faults are both active and cause a series of aftershocks with different focal mechanism solutions. Some aftershocks are also detected at the northern end of the Jiaolin fault and the southern end of the Shiwo fault. The focal mechanism solutions of these events are mostly of thrust type and strike-slip type with poor consistency, which proves that many faults in these areas began to be active after the Beiliu earthquake. However, the specific trigger mechanism is still indistinct.

图 1地震及台站分布图

地震及台站分布图

Figure 1.Map of earthquakes and stations

Map of earthquakes and stations

图 2地震目录中4次地震事件波形

地震目录中4次地震事件波形

Figure 2.Waveforms of 4 earthquake events in regional earthquake catalog

Waveforms of 4 earthquake events in regional earthquake catalog

图 3959台站24小时连续波形检测结果

959台站24小时连续波形检测结果

Figure 3.24 hours continuous records and detection results of earthquakes

24 hours continuous records and detection results of earthquakes

图 4不同台站同一地震事件的波形

不同台站同一地震事件的波形

Figure 4.Waveforms recorded by different stations of the same earthquake

Waveforms recorded by different stations of the same earthquake

图 5单台站余震识别结果

单台站余震识别结果

Figure 5.The detection results of single station

The detection results of single station

图 6初定位使用的地壳速度模型

初定位使用的地壳速度模型

Figure 6.Crustal velocity model used for initial locating

Crustal velocity model used for initial locating

图 7初定位结果

初定位结果

Figure 7.Initial locations of the aftershocks

Initial locations of the aftershocks

图 8重定位结果

重定位结果

Figure 8.The results of relocation

The results of relocation

图 9主震附近重定位结果

主震附近重定位结果

Figure 9.3D view of relocation results near main shock

3D view of relocation results near main shock

图 10震源机制解结果

震源机制解结果

Figure 10.The results of focal mechanism solution

The results of focal mechanism solution

图 11主震附近震源机制解结果

主震附近震源机制解结果

Figure 11.The results of focal mechanism solution near the mainshock

The results of focal mechanism solution near the mainshock

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