Complex rupture of the 2 April 2024 MW 7.4 Hualien earthquake inferred from seismic and geodetic observations

Abstract

The rupture process of the 2024 Hualien M_W 7.4 earthquake was investigated through a joint inversion of seismic and geodetic datasets, revealing a complex multi-faulting event involving four fault segments that ruptured coseismically. The rupture initiated on a southeast-dipping reverse fault (F1) at a depth of 20 km. Six seconds later, slip propagated onto a conjugate reverse fault (F2), intersecting F1 at a depth of 34.5 km. Subsequent ruptures occurred on fault segments to the north; F3 at 20 s, with normal faulting mechanism, followed by overlying thrust fault F4 at approximately 33 s. The rupture propagated progressively toward the northeast, extending roughly 80 km along strike, with an average rupture velocity of ∼2.5 km/s. The heterogeneous slip distributions have peak slip of ∼4 m near the intersection of F1 and F2, accompanied by complementary aftershock patterns. The total seismic moment is estimated as 1.53 × 10²⁰ N·m, with the majority released within the first 35 s, predominantly on F1 and F2. Notably, we identified depth-dependent rise time patterns on the main fault, with longer rise times at shallower depths. This study provides new insights into multi-fault interactions during a major earthquake rupture, particularly the dynamics of conjugate faulting in continental collision zones, which can guide seismic hazard assessments and more realistic simulations of complex suture zone fault behavior.