Surface ruptures of the 2022 Guanshan-Chihshang earthquakes in central Longitudinal Valley area, eastern Taiwan

• Published in: TAO : Terrestrial, atmospheric, and oceanic sciences Vol. 35; no. 1; pp. 16 - 25
• Main Authors: Wang, Yu, Wu, Sheng-Han, Chou, Hoi Ling Birdie, Li, Yi-Yu, Cheng, Wai San, Ho, Andrew, Chen, Jian-Ming, Liu, Sze-Chieh, Hsieh, Chia-Yun, Duan, Siang, Saw Myat Min, Ei Mhone Nathar Myo, Tsai, Yuan-Lu, Liang, Nai-Wun, Liao, Jhih-Hao, Lam, Tsz Yau Amundsen, Chang, En-Wei, Shyu, J. Bruce H.
• Format: Journal Article
• Language: English
• Published: Singapore Springer Nature Singapore 01.12.2024; Chinese Geoscience Union (Taiwan); Springer
• Subjects: 2022 Guanshan and Chihshang earthquakes; Atmospheric Sciences; Central Range fault; Deformation; Earth and Environmental Science; Earth Sciences; Earthquake damage; Earthquakes; Elastoplasticity; Fault lines; Fault scarps; Geological faults; Geology; Lateral displacement; Longitudinal Valley; Oceanography; Original Article; Post-seismic afterslip; Residential areas; Rice fields; Rupture; Rupturing; Sediments; Seismic activity; Seismic response; Surface rupture; Valleys; Yuli fault; Philippine Sea; Taiwan; Yuli fault; Central Range fault; Post-seismic afterslip; Longitudinal Valley; Surface rupture; 2022 Guanshan and Chihshang earthquakes
• ISSN: 1017-0839; 2311-7680
• DOI: 10.1007/s44195-024-00077-3

The Mw 6.4 and 6.8 Guanshan-Chihshang earthquakes occurred on 17 and 18 September 2022 resulted in prominent surface ruptures within the Longitudinal Valley in eastern Taiwan, particularly along the Yuli fault. Approximately 18 h after the mainshock, we began to document the surface rupture near Yuli Town. Our result suggests the surface rupture formed a confined single left-lateral trace in the town of Yuli, characterized by a series of en échelon right-stepping left-lateral faulting geometry. The rupture of 2022 roughly matches the locations of 1951 surface ruptures inside Yuli Town, with a similar amount of left-lateral cross-fault displacement. North and South of the Yuli residential area, we identified several sections of the surface rupture distributed in the water-saturated paddy fields. The maximum left-lateral displacement recorded across the rupture can reach 1.4 m just south of Yuli, with the fault scarp resembling a high-angle west-dipping fault geometry. In addition to the co-seismic surface ruptures, our repeating cross-fault measurements show significant post-seismic shallow after-slip along the Yuli fault. The amount of post-seismic deformation within 3 months after the mainshock is close to, or even higher than the co-seismic cross-fault displacement, consistent with local witness accounts and post-event field photos which showed continuous damage and displacement of building floors and roads after the earthquake. Such shallow post-seismic slips were also observed along the main fault trace in the 2014 South Napa earthquake, and likely represent the shallow elastoplastic behavior of the sub-vertical fault in the young alluvial sediments. Key points We documented surface ruptures and cross-fault displacements in the vicinity of Yuli after the 2022 Guanshan-Chihshang earthquakes. The surface ruptures in Yuli showed clear left-lateral displacements along the previously mapped Yuli fault that ruptured in November 1951. Rapid and persisted after-slip was observed along this section of the Yuli fault trace.