Construction of high-precision 2019 earthquake catalog and discussion on seismogenic structures in Rongxian-Weiyuan-Zizhong area, Sichuan Province
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摘要:
2019年9月8日四川威远MS5.4地震和12月18日资中MS5.2地震位于“长宁-威远国家级页岩气产业示范区”，地震发生后备受工业界、地震学界和政府的高度关注. 将深度学习方法与传统定位方法相结合，快速构建高精度地震目录，对充分高效利用地震波形资料，提升地震检测能力，分析地震序列的时空演化特征、讨论发震构造模型和发震机制具有十分重要意义. 本文利用最新发展和应用较广的震相自动拾取技术(PhaseNet)、快速震相自动关联技术(REAL)，对荣县—威远—资中附近22个临时地震监测台站四个多月连续记录的波形进行初至P和S波震相拾取、震相自动关联和初步定位，并先后应用传统绝对定位和相对定位技术，获得了荣县—威远—资中地区高精度地震目录，据此利用断层三维建模技术构建了威远MS5.4和资中MS5.2两次地震的发震断层三维几何结构模型，揭示出威远MS5.4和资中MS5.2两地震序列具有相类似的空间分布特征，且空间分布形态与震源机制解一致，结合断层三维几何结构模型，推测两次地震发震构造为同一条先存隐伏逆冲断层，且与流体孔隙压力扩散致使断层活化有关，威远MS5.4地震的发生对资中MS5.2地震具有一定的触发作用. 此外，荣县地区的地震活动分布也同样揭示了逆冲断层活动性质，密集小震级事件活动也与水力压裂具有一定关系.
Abstract:Occurrence of the Sept. 8, 2019 Weiyuan MS5.4 and Dec. 18, 2019 Zizhong MS5.2 earthquakes one after another, which are located in the Changning-Weiyuan National Shale Gas Demonstration Zone, has attracted more attentions from the industry, seismological community and government. Combining the deep learning phase-picking method with the traditional earthquake relocation method to rapidly construct a high-precision earthquake catalog is crucial for the effective utilization of seismic waveform data, improving microseismic detection capabilities, analyzing spatiotemporal seismic evolution characteristics, and investigating seismogenic structural models and earthquake mechanisms of earthquake sequences. In this study, we use the latest developed and widely-used seismic phase automatic picking method (PhaseNet) and phase association method (REAL) to analyze the more than four-month-long continuous waveform recordings from the 22 temporary seismic stations in the Rongxian-Weiyuan-Zizhong area. We first pick seismic P and S first arrival phases using PhaseNet and the REAL to associate with a particular earthquake, with preliminary locations determined by grid search. The Hypo-Inverse absolute relocation and HypoDD methods are successively used to obtain the high precision relocated earthquake catalog in the Rongxian-Weiyuan-Zizhong area. Based on the relocated earthquake catalog, 3D fault modeling techniques are employed to construct seismogenic fault models for the Weiyuan MS5.4 and Zizhong MS5.2 earthquakes. The relocated earthquake catalog reveals the spatiotemporal distribution characteristics of the Weiyuan MS5.4 and Zizhong MS5.2 earthquake sequences, supported also by the corresponding earthquake focal solutions. Integrating with the 3D geometric structural model of the fault, it can be inferred that the seismogenic structures responsible for both earthquakes are linked to a common, pre-existing thrust fault, whose activation is plausibly associated with the diffusion of fluid pore pressure. Notably, the occurrence of the Weiyuan MS5.4 earthquake appears to play a pivotal role in triggering the Zizhong MS5.2 earthquake. In addition, the seismic distribution within the Rongxian area also reveals the activity of thrust fault. The intensive occurrence of small-magnitude earthquakes demonstrates an apparent correlation with hydraulic fracturing activities.
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Key words:
- Deep learning method /
- PhaseNet /
- HypoDD /
- Seismogenic structure /
- Spatiotemporal evolution /
- Weiyuan earthquake /
- Zizhong earthquake
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图 1
研究区域地震与地震监测台站分布图(黑色三角形为新建荣县—威远—资中地震台阵临时监测台站位置；Lei et al., 2019；Meng et al., 2019；雷兴林等, 2020；易桂喜等， 2020)
Figure 1.
Map showing distributions of earthquakes and seismic stations used in this study (Black triangles indicate the locations of the newly installed seismic stations in the Rongxian-Weiyuan-Zizhong seismic array，Lei et al., 2019；Meng et al., 2019；Lei et al. , 2020；Yi et al.， 2020)
图 2
威远MS5.4地震发生当天BST地震监测台站垂直分量连续波形记录
Figure 2.
Continuous waveforms of the vertical components recorded by the BST seismic monitoring station
图 3
震级-频次-日频次时间统计图
Figure 3.
Time statistics graph of magnitude-frequency-daily frequency
图 4
REAL自动关联地震目录合理性验证图
Figure 4.
Rationality verification diagram of REAL earthquake catalog
图 7
不同地震目录的地震分布对比
Figure 7.
Comparison map of the earthquake distributions from different earthquake catalogs
图 5
CENC提供的169个参考地震的震级(MCENC)与计算地方震级(ML)关系图
Figure 5.
Plot of CENC magnitude (MCENC) versus calculated magnitude (ML) of the 169 reference earthquakes selected from the CENC Catalog
图 6
人工验证震相统计与走时震中距曲线
Figure 6.
Manually-verified phase statistics and travel-time vs. epicenter distance curve
图 8
不同地震目录与人工地震目录的地震事件对比
Figure 8.
Comparison map of the earthquake events between the different catalogs and the CENC catalog from August 13 to December 31, 2019
图 9
威远—资中地区重新定位地震分布
Figure 9.
Distributions of the relocated earthquakes in the Weiyuan-Zizhong area
图 10
威远—资中地区威远MS5.4地震和资中MS5.2地震序列分布
Figure 10.
Map showing seismic sequences before and after the Weiyuan MS5.4 and Zizhong MS5.2 earthquakes
图 11
荣县地区重定位地震活动分布
Figure 11.
Distributions of the relocated earthquakes in the Rongxian area
图 12
发震断层三维几何结构模型与余震时空演化分布
Figure 12.
Detailed 3D seismogenic fault geometry and spatiotemporal evolution distribution of aftershocks on the fault
图 13
威远MS5.4和资中MS5.2地震震源区地震活动时空迁移特征
Figure 13.
Spatiotemporal migration characteristic of seismic activity in the source area of Weiyuan MS5.4 and Zizhong MS5.2 earthquakes
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