Unveiling Tectonic Complexities in the 2024 Hualien (eastern Taiwan) Earthquake Sequence Using GNSS and InSAR Data

Taiwan, located at the convergent boundary between the Philippine Sea and Eurasian plates, is one of the most seismically active regions globally, with convergence rates reaching 80-90 mm/yr. The Longitudinal Valley suture zone in eastern Taiwan, accommodating ~30 mm/yr of NNW-SSE shortening, hosts two major reverse fault systems: the E-dipping Longitudinal Valley Fault (LVF) and the W-dipping Central Range Fault (CRF). These faults exhibit complex interactions, particularly in the northern sector of the Longitudinal Valley, where cross-cutting relationships and evolving tectonic dynamics generate significant seismotectonic complexity.

The 2 April 2024 M_W 7.4 Hualien earthquake, the strongest instrumentally recorded event near Hualien since the 1951 sequence, exemplifies this complexity. Previous seismic events in this region have been associated with ruptures on both E- and W-dipping faults, reflecting the dynamic interplay between these systems. To investigate the faulting processes and source parameters of this sequence, we analyzed an extensive geodetic dataset, integrating Global Navigation Satellite Systems (GNSS) and Interferometric Synthetic Aperture Radar (InSAR) observations. Elastic dislocation modeling was applied to constrain the rupture geometry and evaluate the interaction between fault segments. GNSS and InSAR data from the 2024 event reveal a rupture pattern involving multiple fault segments, consistent with observations of focal mechanisms, aftershock distributions, and long-term moment release patterns. Although simple single-fault models (e.g., an E-dipping Longitudinal Valley Fault or a W-dipping Central Range Fault) can explain the geodetic data, a composite fault model, incorporating multiple segments, better accounts for the observed displacements, seismicity, and the complex structure of the northern Longitudinal Valley. Our findings provide new insights into the seismogenic processes and fault dynamics underlying this significant seismic event. They highlight the evolving tectonic setting of eastern Taiwan and contribute to the understanding of the processes driving seismotectonic complexity in one of the most tectonically active regions of the world.