The 2025 Mw7.6 Aomori-Oki Megathrust Sequence and a Slip-Parallel Seismic Belt to the Trench

The 2025 Mw 7.6 Aomori-Oki earthquake nucleated near the 1968 Mw 8.3 Tokachi-Oki rupture area. Our waveform inversion reveals a highly asymmetric rupture extending ~100 km along-dip; large slip (>1 m) extended ~40 km northward from the hypocenter, overlapping the inferred 1968 northern asperity. Minor slip (0.2–0.6 m) extended ~80 km updip, and high-precision relocations show that major aftershocks, including the Mw 6.7 and 6.6 events, clustered near the updip limit. These aftershocks form multiple streaks aligned with plate convergence. Terminating one such streak, the Mw 6.7 sequence formed a dense circular cluster correlating with a bathymetric high. The 2025 Aomori-Oki sequence and historical M≥5 events define a continuous slip-parallel belt that traverses a prominent tremor gap to reach the trench. We propose that the spatial organization of the seismic zone and streaks is modulated by the interplay between subducting slab roughness and inherited upper-plate structures.