Coseismic Slip of the 2024 Mw 7.3 Hualien Earthquake Constrained by GNSS Observations

We use coseismic GNSS data to estimate the source fault parameters and coseismic fault slip of the Mw 7.3 earthquake that occurred in Hualien City, Taiwan on 3 April 2024. We examined three coseismic fault scenarios, that is Model 1, Model 2, and Model 3, because of the elusive fault system in the coseismic region. In Model 1 and Model 2, the coseismic displacements were explained by a single source fault dipping to the east and west, respectively. In Model 3, we considered a combination of an east-dipping and a west-dipping fault. For Model 1-3, we explore the geometry parameters of source fault plane(s) and invert the coseismic fault slip through a Bayesian method. Although Model 1 and Model 2 produce reasonable fits to GNSS data, Model 3 better reproduces the first-order pattern of the GNSS data. In Model 3, the east-dipping fault accounts for most of the moment release of this earthquake with a thrust slip up to about 1.5 m. The slip on the west-dipping fault in Model 3 is smaller with a maximum slip of about 0.4 m. We calculate the Coulomb stress in Model 3 on major active crustal faults in this region. The Coulomb stress on the Longitudinal Valley Fault and Milun Fault increased by 21 and 5 bars, respectively, implying a higher seismic potential in the future.