Eroding asperities imply larger locked regions on subduction megathrusts

Interseismic fault coupling is commonly inferred from slip-deficit inversions of geodetic data, yet these approaches enforce smoothing and suppress negative stressing rates, limiting their ability to resolve locking distributions consistent with expectations from numerical simulations and theoretical considerations. Here we apply a physics-informed inversion that allows locked asperities to evolve through creep-front encroachment, producing sharp locked-to-creeping transitions and process zones with negative stressing rates. Across Cascadia, Hikurangi, and Nankai, we find that models with eroding asperities require substantially larger locked areas than stationary inversions, despite yielding nearly identical total moment accumulation rates. Moment accumulation within eroding asperities is 2–3 times higher in Cascadia and Hikurangi and ~50\% higher in Nankai, reflecting enhanced creep surrounding process zones that must be balanced by larger asperities to satisfy geodetic moment constraints. These results imply that conventional inversions may systematically underestimate the areal extent of strongly coupled patches. Moreover, consistently inferred negative stressing rates indicate that locked asperities are shrinking, suggesting that present-day coupling maps capture only a transient phase of an evolving state of megathrust locking. Our findings highlight the need to treat interseismic locking as a dynamic process and call for examination of coupling-based assessments of seismic potential in this light.