Relationships Between Plate Interface Deformation and Earthquake Segmentation

Prediction of subduction earthquakes mostly relies on interplate coupling models that provide patterns interpreted within the framework of rate-and-state friction laws. However, this framework has been challenged by recent observations, indicating that rheological and geometrical complexities must be considered in order to fully understand megathrust mechanics.

In this study, we investigate whether the strongly and weakly coupled patches could be related to the distribution of deformation along the plate interface, potentially associated with either basal erosion or underplating. Since both underplating and basal erosion impact forearc morphology, the location of such distributed deformation along the plate interface can be inferred from a simple mechanical analysis of the topography.

We first show that long-lived plate interface deformation is governed by aseismic processes. Through a comparison of erosive and accretionary margins, we show that large earthquakes propagate along well-localized and smoothed rate-weakening fault planes, bounded by elongate zones of underplating along accretionary margins, and by both basal erosion and underplating along erosive margins.

Comparing margins of different ages, we find that underplating occurs at shallower depth for younger subducting plates. Along erosive margins, two bands of underplating are observed: the shallow one likely corresponds to the underplating of eroded material, while the deeper would be related to the underplating of the altered oceanic plate. In cold subduction zones, Domain-C earthquakes take place between those two bands, while SSEs are found along warm subduction zones. These differences are discussed using thermo-mechanical simulations.