THE STRESS STATE IMPLIED BY DISLOCATION MODELS OF SUBDUCTION DEFORMATION

Dislocation models of the earthquake cycle are often employed to predi ct surface deformations above a subduction zone. However, these models , being based entirely on a kinematic formulation of subduction behavi our, place no constraints on the subsurface stress held. Here, the str ess state predicted by an elastic dislocation model is shown to exhibi t characteristics inconsistent with those anticipated based on physica l models of subduction behaviour. In particular, the model predicts an unreasonable distribution of stress along the interface between the o verriding and subducting plates. The net shear traction integrates to zero along the interface, so significant shear must act on the overrid ing plate in the updip direction, opposite to that of the relative dir ection of motion of the subducting slab. Quantitative calculations usi ng an elastic half-space representation of the Earth are employed to i llustrate the inconsistencies inherent in the dislocation model. Analy tic expressions for this case are extended to allow for calculation of the stress components over the entire half-space.