Complex Multipatch Rupture and Aftershock Characteristics of the 2024 Mw 4.2 Buan, Korea, Earthquake Sequence

Moderate-magnitude earthquakes in stable continental regions (SCRs) can pose significant hazards, yet their rupture processes remain poorly understood due to sparse instrumentation and their infrequent occurrence. The 2024 Mw 4.2 Buan, Korea, earthquake, and its aftershock sequence were exceptionally well recorded by a local seismic network, providing a rare opportunity to investigate the rupture process of a moderate-magnitude earthquake in an SCR. Focal mechanisms and high-precision relocations reveal multiple fault strands activated during the eight-month-long sequence. Using an aftershock as an empirical Green’s function, we retrieve relative source time functions of the mainshock, which are subsequently used to construct a detailed slip model. We apply two different rupture modeling approaches: a two-patch modeling with elliptical subfaults and a linear slip inversion. Both approaches consistently reveal two spatially distinct, high-stress-drop patches that ruptured sequentially, with a short temporal overlap, indicating notable rupture complexity. Furthermore, both on-fault and off-fault aftershocks appear to have been triggered by static stress increases associated with the mainshock rupture.