Nearby faults interact through stress changes induced by fault slip and viscoelastic flow. The process is, however, often elusive and can be geometry-dependent and time-variant. Research groups from Academia Sinica, National Taiwan University, and National Chung Cheng University combine geodetic and field observations to characterize the interaction of two head-to-head, conjugate faults in eastern Taiwan during the 2022 Chihshang earthquake sequence. We map the coseismic slip on the Central Range fault and dynamically-triggered shallow slip on the Longitudinal Valley fault, which has been creeping interseismically. Overlapping of seismic and aseismic slip suggests that the Longitudinal Valley fault is capable of hosting a variety of distinct slip behaviors. Moreover, substantial slip on the Central Range fault suppresses Coulomb stress on the Longitudinal Valley fault, and vice versa, resulting in seismic bursts in an out-of-phase pattern on the two faults as seen in the hundred-year historical records. Such fault interaction implies the need for time-dependent seismic hazard reassessment for the complex fault system. The research paper has been published in Communications Earth & Environment on September 21, 2023. [https://doi.org/10.1038/s43247-023-00994-0]
Coseismic slip during the Guanshan-Chihshang earthquake sequence. (a) kinematic model. Brown contours and colored patches represent the slip during the Guanshan and Chihshang earthquakes, respectively. Gray circles are aftershocks between the two events. (b) Source time functions. Gray plot represents the Guanshan earthquake on the Central Range Fault. Black plot and orange curve represents the Chihshang earthquake on the Central Range Fault and Longitudinal Valley Fault, respectively. (c-d) Rupture process of the Guanshan earthquake. (e-g) Rupture process of the Chihshang earthquake.