Geodetic observations of interseismic surface deformation in the vicinity ofsubduction zones are frequently interpreted using simple kinematic elastic dislocationmodels (EDM). In this theoretical study, we develop a kinematic EDM that simulates platesubduction over the interseismic period (the elastic subducting plate model (ESPM))having only 2 more degrees of freedom than the well-established back slip model (BSM):an elastic plate thickness and the fraction of flexural stresses due to bending at the trenchthat are released continuously. Unlike the BSM, in which steady state deformation in bothplates is assumed to be negligible, the ESPM includes deformation in the subductingand overriding plates (owing to plate thickness), while still preserving the correct sense ofconvergence velocity between the subducting and overriding plates, as well as zero netsteady state vertical offset between the two plates when integrated over many seismiccycles. The ESPM links elastic plate flexure processes to interseismic deformation andhelps clarify under what conditions the BSM is appropriate for fitting interseismicgeodetic data at convergent margins. We show that the ESPM is identical to the BSM inthe limiting case of zero plate thickness, thereby providing an alternative motivation forthe BSM. The ESPM also provides a consistent convention for applying the BSM to anymegathrust interface geometry. Even in the case of nonnegligible plate thickness, thedeformation field predicted by the ESPM reduces to that of the BSM if stresses related toplate flexure at the trench are released either continuously and completely at shallowdepths during the interseismic period or deep in the subduction zone (below 100 km).However, if at least a portion of these stresses are not continuously released in the shallowportion of the subduction zone (via seismic or aseismic events), then the predicted surfacevelocities of these two models can differ significantly at horizontal distances from thetrench equivalent to a few times the effective interseismic locking depth.
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