Effects of the 2022 Mw 7.0 Chihshang Earthquake on the Shallow Creeping of the Central Longitudinal Valley Fault in Eastern Taiwan: Insights from Precise Leveling Measurements

Abstract This study investigated the effects of the 2022 Mw 7.0 Chihshang earthquake in eastern Taiwan on the shallow creeping of the central Longitudinal Valley fault (LVF). Precise leveling surveys were conducted along the Ruisui-Dewu, Yuli, and Dongzhu routes over the LVF. Before the earthquake, previous leveling surveys had detected deformations caused by stable fault creeping of the LVF. Interseismic linear trends and coseismic deformations were removed from the leveling data. Two shallow faults at 1 km were estimated from the corrected-coseismic deformation for the Yuli route. A shallow fault at 1 km and a deep fault at 5 km were estimated from the interseismic deformation. A positive delta Coulomb failure function change was calculated for shallow faults due to the creeping movement on the deep fault before the earthquake, and the creeping movement on the deep fault before the earthquake may have promoted the rupture of the shallow fault. The strong Chihshang earthquake most likely triggered the rupture of the shallow fault, on which strain had been concentrated by the interseismic creeping of the deeper fault. In contrast, the accumulated total strain at the deeper part might be quite low due to a strain release process for a steady creeping movement on deep fault in the interseismic period. The significant slip was not induced in the coseismic period. Although significant slip occurred in the shallower part, the slip might not be induced in the deeper part adjacent to the asperity of the LVF. In the Dewu route, the observed large west-side-uplift is attributed to the coseismic rupture of the Chihshang earthquake. In the Dongzhu route, an interseismic east-side-uplift by a creeping fault and a coseismic west-side-uplift were observed at the same location, indicating a local tensile stress field by the Chihshang earthquake.