Multi-scale numerical modelling of subduction interface rheology

The physical nature and the rheology of the subduction interface play an important role in the deformation of the overriding plate, the degree of locking of the subduction zone plate boundary, and the rate of subduction. Here, we employ the Finite Element Method (FEM) to determine the effect of matrix rheology on the bulk interface deformation. We use the open-source particle-in-cell FEM code Underworld (Moresi et al., 2007) to create synthetic 2D visco-plastic models of the subduction interface that deform by simple shear. The models comprise meter-scale blocks of continental affinity encompassed within a metasedimentary matrix. We investigate the effect of constant, Newtonian, and non-Newtonian matrix viscosities on the deformation and stress distribution in the models for large finite shear strains. We vary the percentage of block concentration from 10% to 65%, as well as the shear velocity while making sure the strain rates produced remain within the interseismic range, and we calculate strain localization and stresses within the models. Finally, we use the same viscosity formulations in large-scale 2D models of a subduction zone to investigate their influence on upper plate deformation and subduction rate during the interseismic stage. With this multi-scale analysis, we gain insight into how the same rheological law can affect deformation at different scales.