Do Coupled Megathrusts Rupture?

Bar Oryan , Alice-Agnes Gabriel

Megathrust earthquakes are among the most destructive and least predictable natural hazards. Kinematic geodetic coupling models, which identify regions of the plate interface where interseismic strain accumulates, are essential for seismic and tsunami hazard assessment. Yet their reliability remains debated: geodetic records are short, offshore resolution remains poor, and earthquake ruptures may propagate dynamically across both creeping and locked slab portions. This uncertainty has limited our ability to assess whether large earthquakes release strain where coupling is strongest or rupture independently of interseismic coupling. Here we present the first systematic global analysis of slip-coupling relationships, compiling 61 earthquake slip models (Mw 6.7–9.1) across 12 subduction zones. We find that slip–coupling correlations strengthen with earthquake magnitude across margins. Events above Mw 8.7 release about half of their slip where coupling exceeds 0.8, compared with a tenth for events below Mw 7.5. Large earthquakes therefore release strain accumulated in strongly coupled regions, whereas coupling provides weaker constraints on moderate-earthquake rupture, which may reflect limited resolution, evolving locking or rupture arrest. Our results link coupling models to coseismic slip, showing where large earthquakes release strain and why anticipating the hazard posed by the more frequent moderate earthquakes require denser, longer geodetic records.