Coseismic Deformation and Interaction of the 2022 ML 6.6 Guanshan and ML 6.8 Chihshang Earthquakes in Southeastern Taiwan Revealed by Strong-Motion Data

Abstract Two subsequent strong earthquakes—the ML 6.6 Guanshan and the ML 6.8 Chihshang earthquakes—struck southeast Taiwan on 17 and 18 September 2022, causing extensive damage associated with multiple fault systems. Mapping their coseismic deformation is crucial for constraining the slip behavior and possible fault interaction. To enhance the coverage and resolution of the coseismic deformation features for the two events, data from two dense strong-motion networks are utilized to retrieve coseismic displacements using a two-stage baseline correction method. The reliability of derived displacements is validated with cosite Global Navigation Satellite Systems (GNSS) data. The denser distribution of the seismic stations supplements the GNSS and seismic data previously reported and reveals a more detailed view of regional and near-fault deformation. The integrated results confirm that the surface ruptures caused by the Chihshang earthquake are located to the east of the responsible Central Range fault, north of the epicenter. The complex coseismic deformation pattern of the Guanshan earthquake indicates the possible involvement of local structures especially around Taitung. More critically, localized subsidence created by the southward rupture propagation of the Guanshan earthquake is depicted between the epicenters of the two earthquakes. This subsidence may impart large stress on the northern segment of the fault and trigger the Chihshang earthquake. The enriched near-fault deformation patterns revealed by our newly compiled dataset offer valuable constraints for understanding shallow slip distribution, shallow versus deep slip budget, and possible multifault interaction in future investigations.