Coseismic Slip of the 2024 Mw 7.3 Hualien Earthquake Constrained by GNSS Observations and Its Implications for Fault Interactions

On 2 April 2024, an Mw 7.3 thrust earthquake occurred in Hualien City, Taiwan. In this study, we examined three coseismic models, that is model 1 (an east-dipping fault), model 2 (a west-dipping fault), and model 3 (a combination of an east-dipping and a west-dipping fault). For each model, the geometry of the fault plane(s) and coseismic fault slip were determined through a Bayesian method based on the coseismic Global Navigation Satellite Systems (GNSS) displacements. Although models 1 and 2 both produce reasonable fits to GNSS data, with corresponding average root mean square (rms) misfits of 16.4 and 20.0 mm, respectively, model 3 better reproduces the first-order pattern of the GNSS data and achieves a smaller average rms misfit of 15.2 mm. Based on the rms misfit, Akaike information criterion, and Bayesian information criterion, model 3 is identified as the optimal model. Model 3 features thrust slips on the east-dipping fault, with a maximum slip of 1.45 m. The Longitudinal Valley and Milun faults undergo a coseismic Coulomb stress increase of up to 21 and 5 bars, respectively, increasing the seismic potential in the future.