The 16 July 2025 Mw 7.3 Earthquake in Shumagin Islands: Another Intraplate Strike-Slip Event Related to the Heterogeneous Coupling Distribution on Alaska Subduction Interface

Abstract The heterogeneous coupling distribution on subduction interface not only influences the slip distribution of megathrust earthquakes but also plays a critical role in facilitating intraplate strike-slip events. On 16 July 2025, an Mw 7.3 strike-slip earthquake struck the Shumagin segment of the Alaska Peninsula, raising questions about its seismogenic fault orientation and mechanical origin. Using artificial intelligence-enhanced detection and relocation of the seismic sequence, we constructed an east–west trending, south-dipping, curved seismogenic fault model. Joint inversion of teleseismic waveforms and Global Navigation Satellite System data reveals a predominantly sinistral strike-slip mechanism, and the rupture was confined largely beneath the subduction interface, indicating that it is an intraplate event. Together with the nearby 2020 Mw 7.6 dextral strike-slip earthquake, the two events form a conjugate fault system. We demonstrate that both earthquakes, though differing in strike direction, can be explained by the stress perturbations arising from along-strike and along-dip variations in megathrust coupling, acting in concert with the background stresses from slab pull and plate bending. These findings underscore the widespread influence of coupling heterogeneity in influencing strike-slip earthquake generation in subduction zones and call for a reassessment of related seismic hazards in regions such as the Semidi segment.