A viscoelastic coupling model for the cyclic deformation due to periodically repeated Earthquakes at subduction zones

<jats:p>Vertical displacements due to periodic reverse faulting events in an elastic plate overlying a viscoelastic (Maxwell) half space are obtained and compared with the observed deformation cycle (coseismic strain release, postseismic transients, interseismic strain accumulation) from Japan. The viscoelastic effects, including the influence of buoyant restoring forces, are obtained using the method developed by Rundle, and plate convergence and strain accumulation are incorporated following the procedure suggested by Savage. The resulting deformation cycle is compared with that of an analogous elastic half‐space dislocation model in which postearthquake effects are due to transient aseismic slip below the coseismic fault. Cyclic deformation is similar but not identical for the two models, and observations from southwest Japan suggest the superiority of the viscoelastic coupling model. In particular, inclusion of the effects of steady state flow in the asthenosphere overcomes a defect of the elastic half‐space model and results in agreement with the observed interseismic movement pattern. Several aspects of the postseismic deformation, its landward migration, and its transition to the interseismic phase of the cycle are explained as well, but the short duration of near‐trench transients relative to those observed farther inland is not matched. The success of a buried slip model in explaining early postseismic near‐trench movements and asthenospheric flow in accounting for cumulative postearthquake transient motions suggests the existence of a transition zone between lithosphere and asthenosphere whose behavior is brittle/elastic in the short term and ductile for longer‐term deformation, and such a modification may reconcile remaining discordant observations. However, reasonable variations in coupling model parameters cannot account for observed differences in the deformation cycle in other parts of Japan, and these regional differences remain unexplained.</jats:p>