THE RUPTURE PROCESS INVERSION OF SEPTEMBER 2022 ML6.6 AND ML6.83 EARTHQUAKES IN TAIWAN ISLAND, CHINA

doi:10.3969/j.issn.0253-4967.20240045

Abstract

Abstract:

The Taiwan Island is located at the tectonic junction of the western Pacific subduction zone and the Eurasian continental margin, where complex plate subduction, collision, and strike-slip motions have collectively shaped the region’s intense tectonic activity and frequent seismic hazards. The NNE-trending Longitudinal Valley Fault(LVF) in eastern Taiwan serves as a major tectonic boundary separating the Eurasian Plate and the Philippine Sea Plate. It is also recognised as one of the world’s most renowned seismically active zones. On September 17 and 18, 2022, two destructive strong earthquakes with magnitudes of M_L6.6(M_W6.5)and M_L6.83(M_W6.9)successively occurred in the southern segment of this fault. According to high-precision seismic observations from “Taiwan’s Central Weather Bureau(CWB)”, the epicenters of the two events are only 11km apart, with a time interval of 17 hours, indicating significant spatiotemporal clustering. Notably, the focal mechanisms of the two earthquakes differ distinctly: the September 17 event was a typical left-lateral strike-slip earthquake, while the September 18 event displayed a more complex composite rupture mechanism dominated by thrust motion with a significant strike-slip component. This rapid transition in tectonic deformation modes within a short period reflects the complex stress environment of the region, providing a unique natural laboratory for revealing the fine-scale dynamic processes of the fault zone and the interaction mechanisms between consecutive earthquakes.

To systematically analyse the source rupture processes and stress triggering relationships of these two strong earthquakes, this study collected near-field strong-motion records and precise hypocenter locations from the CWB, combined with source parameters released by the United States Geological Survey(USGS). Using the Iterative Deconvolution and Stacking(IDS)technique, we performed detailed kinematic inversions of the rupture processes of both events. Furthermore, leveraging the high temporal resolution advantage of seismic waveform data, we successfully isolated the co-seismic deformation fields for each earthquake, providing crucial evidence for understanding the interaction mechanisms within the earthquake sequence. The inversion results show that the rupture durations of the two earthquakes are 27s and 48s, respectively, and that the spatial patterns of fault slip distribution are significantly different: the September 17 earthquake exhibited a single-peak slip distribution concentrated southwest of the epicenter, with a maximum slip of 1.06m. In contrast, the September 18 earthquake displayed a double-peak slip pattern predominantly distributed northeast of the epicenter, reaching a maximum slip of 3.19m and featuring a typical asymmetric bilateral rupture. The slip depths of both earthquakes are distributed within the range of 0-30km, consistent with regional seismotectonic characteristics.

Quantitative analysis of Coulomb failure stress changes demonstrated that the September 17 earthquake induced significant static stress perturbations in the rupture area of the September 18 event, exceeding the seismic triggering threshold. Our results strongly support the domain role of static stress transfer in this earthquake sequence. Further analysis revealed that the September 18 earthquake had a higher stress drop, which may be closely related to its complex rupture mechanism and larger slip magnitude.

Through high-resolution source rupture process inversion and Coulomb stress change calculation, this study systematically revealed the rupture differences, spatiotemporal evolution laws, and intrinsic triggering mechanisms of the short-time sequence strong earthquakes along the LVF in Taiwan, China. It not only confirms the importance of stress transfer between earthquakes but also highlights the complexity of seismic rupture processes(e.g., the diversity of rupture modes and the inhomogeneity of slip distribution). The findings provide important observational evidence for an in-depth understanding of seismic rupture behavior along the LVF, complex tectonic deformation mechanisms at plate boundaries, and the laws of earthquake generation and occurrence. Meanwhile, this study emphasizes the core significance of inter-earthquake interactions for earthquake prediction, hazard assessment, and disaster prevention and mitigation. Additionally, it provides a methodological reference for earthquake sequence research in similar tectonic environments. Future research should further integrate numerical simulations with multidisciplinary observational data to explore the physical mechanisms of seismic rupture processes. Simultaneously, in regions with high seismic hazard, such as Taiwan, China, it is necessary to continuously strengthen the development of high-density seismic network monitoring and multi-parameter early warning technologies, thereby continuously improving comprehensive prevention and control capabilities for seismic disasters and minimizing casualties and economic losses from earthquakes.

Key words: Taiwan Island, China, seismic source rupture mechanisms, stress trigger, coseismic deformation field

摘要：

位于台湾岛东部的NNE向纵谷断裂是一条重要的构造边界带和强震活动带。2022年9月17日、 9月18日分别在纵谷断裂的南部发生了M_L6.6(M_W6.5)、 M_L6.83(M_W6.9)2次强震。根据台湾地区气象局(CWB)提供的地震信息可知2次地震的震中仅相距11km, 发震时间仅相隔17h, 而与9月17日的左旋走滑地震不同的是, 9月18日的地震为逆冲兼走滑地震。文中利用CWB提供的近场强震数据及定位结果, 基于美国地质调查局给出的震源参数, 采用迭代反褶积和叠加(Iterative Deconvolution and Stacking, IDS)方法研究了这2次地震的震源破裂过程和应力触发关系, 并利用地震波数据的高时间分辨率优势分离了这2次地震的同震形变场。结果显示: 2次地震的主破裂分别持续了27s和48s, 断层滑动分布分别呈现单驼峰和双驼峰的形状。9月17日地震的滑动分布集中在震中西南侧, 9月18日地震的滑动分布在震中东北侧, 为不对称的双侧破裂模式, 滑动分布的深度都在0~30km处, 2次地震的累积最大滑动量分别为1.06m和3.19m, 9月17日地震对9月18日地震产生了明显的应力触发作用。这种应力触发作用可能是导致2次地震在短时间内相继发生的重要原因之一。

关键词: 台湾岛, 地震震源破裂过程, 应力触发, 同震形变场

LIU Lian, QU Chun-yan, WU Dong-lin, RONG Yi-lin, CHEN Han. THE RUPTURE PROCESS INVERSION OF SEPTEMBER 2022 M_L6.6 AND M_L6.83 EARTHQUAKES IN TAIWAN ISLAND, CHINA[J]. SEISMOLOGY AND GEOLOGY, 2026, 48(1): 217-232.

刘恋, 屈春燕, 吴东霖, 容伊霖, 陈晗. 2022年9月台湾岛M_L6.6和M_L6.832次地震的破裂过程反演[J]. 地震地质, 2026, 48(1): 217-232.

Figures/Tables 13

Fig. 1 Tectonic background and aftershock distribution of the 2022 double earthquakes in Taiwan, China.

Table1 Source parameters of two Taitung earthquakes in September 2022

机构	发震时间 (UTC)	东经 /(°)	北纬 /(°)	震源深度 /km	走向 /(°)	倾角 /(°)	滑动角 /(°)	震级
CWB	2022-09-17,13:41:19.11	121.1608	23.084	8.61				M_L6.6
	2022-09-18,06:44:15.25	121.1958	23.137	7.81				M_L6.83
USGS	2022-09-17,13:41:17	121.414	23.119	10	202	63	13	M_W6.5
	2022-09-18,06:44:13	121.344	23.138	10	203	69	25	M_W6.9
本文	2022-09-17,13:41:19.11	121.1608	23.084	8.61	202	63	13	M_W6.8
	2022-09-18,06:44.15.25	121.1958	23.137	7.81	203	69	70	M_W7.2

Fig. 2 Inversion flow of source rupture process using IDS method.

Fig. 3 Distribution of strong seismic data stations used for inversion of rupture process.

Fig. 4 Source time function of two earthquakes.

Fig. 5 Cumulative slip distribution of two earthquakes.

Fig. 6 Cumulative change over time of focal fault rupture process of two earthquakes.

Fig. 7 The incremental change in the source rupture process of two earthquakes over time.

Fig. 8 Fitting results of observed and synthetic waveforms for the earthquake on September 17.

Fig. 9 Fitting results of observed and synthetic waveforms for earthquake on September 18.

Fig. 10 InSAR deformation field of double earthquakes separated by seismic wave data.

Fig. 11 Coseismic Coulomb stress changes on the fault surface of the September 18, 2022 earthquake caused by the September 17, 2022 earthquake.

Fig. 12 Influence of the Coulomb stress on the surrounding area caused by the two earthquakes.

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