Simple Crack Models Explain Deformation Induced by Subduction Zone Megathrust Earthquakes

Abstract

Following the 2010 Maule and 2011 Tohoku earthquakes, many studies have examined the relation between megathrust earthquakes and subsequent deformation. Here, we apply simple models based on mode II shear cracks, including approximated effects of the free surface to study induced deformation during coseismic and early postseismic stages. We distinguish between buried and surface ruptures represented by a full‐crack and a half‐crack model, respectively. We adopt an analogy‐based approach to interpret the half‐crack model from well‐known results of the full‐crack model, which is also validated by our numerical simulations. With transferable knowledge between the two models, we provide easy ways to understand (1) the contrasting deformation patterns in the frontal wedge of the overriding plate between buried ruptures and surface ruptures, (2) the correlation between triggered outer‐rise normal faulting and surface ruptures, and (3) the similar deformation patterns for both buried and surface ruptures toward the down‐dip end, with a preference for normal faulting in the overriding plate and for reverse faulting in the subducting plate. These model outcomes are consistent with several recent observations on aftershocks and veins in a paleoaccretionary wedge. We further investigate some important transient features during rupture propagation which show that a transition from compressional to extensional deformation in the frontal wedge of the overriding plate is possible even during a single rupture event. Our work provides alternative views for understanding various aspects of subduction zone megathrust earthquakes and raises the issue of important transient features that were typically ignored in previous studies.

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