Effect of margin curvature on plate deformation in a 3-D numerical model of subduction zones

The large amount of data acquired along most subduction zones underlines the importance of three dimensions in the subduction mechanism. In this work we use a fully 3-D mechanical numerical model to analyse the impact of the plate boundary geometry on the deformation of the upper plate. The model consists of two initially horizontal independent plates overlying an inviscid fluid and continuously pushed towards each other. The initial geometry of the contact zone between the two plates controls the stress regime and the strain pattern in the upper plate. The case with a linear plate boundary and orthogonal convergence is first considered and used as a reference model. With this simple model, the effects of some important parameters (i.e. the interplate friction and the lithosphere-asthenosphere density contrast) are investigated. Finally, cases with curved plate boundaries are considered, and the results are used to shed light on the importance of the dip direction of the interplate plane for the upper plate strain pattern. Unnecessary oceanward convexity causes an accumulation of the subducted material beneath the upper plate and induces an important uplift of the convex area. On the contrary, the material escapes from an oceanward concavity and provokes subsidence in the forearc zone. Such a behaviour induces preferential zones of weakeness in the overriding plate and may allow for explaining some local stress regime variations along convergent margins.