Speaker: Dr. Wei Peng (NSTC research scholar, Dept. of Earth Sciences, National Taiwan Normal University)

Title: Aseismic slip and seismic swarms leading up to the 2024 M7.3 Hualien earthquake

Time: 02:20pm Tuesday 24/Feb/2026

Venue: Room S101, 1F, Lecture Hall (G112)

Abstract:

Understanding the role of aseismic slip in earthquake cycles is essential for assessing seismic hazards and short-term forecasting. Eastern Taiwan’s double-vergence suture zone, where the Philippine Sea Plate subducts beneath the Eurasian Plate, experiences frequent M ≥ 6 earthquakes and widespread aseismic slip, making it an ideal natural setting to study earthquake triggering processes. Using a 24-year catalog of repeating earthquake sequences (RESs) and earthquake swarms, we investigated aseismic deformation leading up to the April 3, 2024 Mw7.3 Hualien earthquake. We find that nine out of ten swarms in the epicentral area, northern Longitudinal Valley, were accompanied by increasing aseismic slip rates, as revealed by RESs on the west-dipping Central Range Fault (CRF). A notable aseismic slip episode in 2021, indicated by GNSS signals, the accelerated RES-derived slip rate, and a four-month-long swarm sequence with high diffusivity (~5.2 m²/s), suggests joint contributions from over-pressured fluids and deep fault creep. This episode was followed by a cluster of M6+ events and a later phase of slightly accelerating seismic and aseismic activity beginning in 2023. Coulomb stress modeling indicates that these aseismic slip events and transient fluid flow increased stress on the CRF, potentially promoting the 2024 mainshock. Our results provide rare evidence for aseismic-slip-induced stress triggering of a major earthquake and highlight the importance of integrating aseismic processes into earthquake hazard models for collisional fault systems.