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 (moment magnitude Mw 6.7–9.1) across 12 subduction zones. We show that large earthquakes (Mw ≥ 7.5) consistently concentrate slip in highly coupled regions, whereas smaller events rupture more variably, almost entirely in weakly coupled areas. These results indicate that major earthquakes predominantly release long-term accumulated strain, while smaller events reflect shorter-term heterogeneity, such as transient asperities, motivating time-dependent coupling models that capture evolving fault strength. Our findings reconcile apparent inconsistencies between kinematic coupling models and seismic slip and establish magnitude-dependent controls on earthquake rupture, with direct implications for seismic hazard assessment.