Numerical modelling of lithosphere–asthenosphere interaction in a subduction zone

We developed a new 2-D numerical approach to study solid–fluid coupling applied to subduction zones. The lithosphere is characterised by an elastic or elastoplastic behaviour and the asthenosphere by a homogeneous isoviscous fluid. The temperature effects are ignored and viscosity and density are constant in time. The solid and the fluid problem are discretised by the finite elements method (FEM). The same solid code used in Hassani et al. [Hassani, R., Jongmans, D., Chery, J., Study of plate deformation and stress in subduction processes using two-dimensional numerical models, J. Geophys. Res. (1997) 102 17951–17965.] has been used to compute the solution of the solid problem. The Stokes problem is solved by a direct solver with a stabilisation procedure. We used a very simple staggered coupling method where the fluid domain is regularly re-meshing. We observed numerical instabilities when the time step is not sufficiently small, especially when strong coupling between the solid and the fluid occurs. We have tested different configurations where the lithosphere is elastic or elastoplastic and show how the slab geometry, the topography and the stress regime in the plates are affected by the viscous resistance of the mantle. We observed that the asthenosphere viscosity is a fundamental parameter in the subduction process. For subduction with an extensional regime in the upper plate, we observe a linear decrease of the extensional stress as a function of the asthenospheric viscosity.