Terrestrial, Atmospheric and Oceanic Sciences (Sep 2024)

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

  • Yu Wang,
  • Sheng-Han Wu,
  • Hoi Ling Birdie Chou,
  • Yi-Yu Li,
  • Wai San Cheng,
  • Andrew Ho,
  • Jian-Ming Chen,
  • Sze-Chieh Liu,
  • Chia-Yun Hsieh,
  • Siang Duan,
  • Saw Myat Min,
  • Ei Mhone Nathar Myo,
  • Yuan-Lu Tsai,
  • Nai-Wun Liang,
  • Jhih-Hao Liao,
  • Tsz Yau Amundsen Lam,
  • En-Wei Chang,
  • J. Bruce H. Shyu

DOI
https://doi.org/10.1007/s44195-024-00077-3
Journal volume & issue
Vol. 35, no. 1
pp. 1 – 25

Abstract

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Abstract 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.

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