A Composite Fault Model for the 2024 MW 7.4 Hualien Earthquake Sequence in Eastern Taiwan Inferred From GNSS and InSAR Data

On 2 April 2024, an M-W 7.4 earthquake struck the northern Longitudinal Valley in eastern Taiwan, about 18 km SSW of Hualien, causing damage and casualties. In this study, we investigated a comprehensive geodetic data set, employing Global Navigation Satellite Systems (GNSS) and Interferometric Synthetic Aperture Radar (InSAR) measurements to assess the rupture geometry associated with earthquake sequence. Although geodetic data can be satisfactorily reproduced by simple single-fault models (i.e., a high-angle E-dipping plane related to the Longitudinal Valley Fault (LVF), or a gentle W-dipping surface associated with the Central Range Fault, CRF), a composite model involving the rupture of different fault segments (a major CRF-related W-dipping fault, a deep segment of the E-dipping LVF, and the Milun Fault) is able to explain the observations, the distribution of seismicity, and the complex structural arrangement of the northernmost sector of the Longitudinal Valley.