A benchmark comparison of subduction models

Schmeling, H.; Babeyko, A.; Enns, A.; Faccenna, C.; Funiciello, F.; Gerya, T.; Golabek, G.; Grigull, S.; Morra, G.; van Hunen, J.

Abstract

Numerically modelling the dynamics of a self-consistently subducting lithosphere is a challenging task because of the decoupling problems of the slab from the free surface. We address this problem with a benchmark comparison between various numerical codes (Eulerian and Lagrangian, Finite Element and Finite Difference, with and without markers) as well as a laboratory experiment. The benchmark test consists of a prescribed setup of viscous flow, driven by compositional buoyancy, and with a low viscosity, zero-density top layer to approximate a free surface. Alternatively, a fully free surface is assumed. Our results indicate that the convergence of the subduction behaviour with increasing resolution strongly depends on the averaging scheme for viscosity near moving rheological boundaries. Harmonic means result in fastest subduction, arithmetic means produces slow subduction and geometric mean results in intermediate behaviour. Complete convergence of results appears mostly beyond presently feasible grid resolution. Analysing the behaviour reveals that this problem is caused by the entrainment of the weak zero-density material into a lubrication layer on top of the subducting slab whose thickness turns out to be smaller than even the finest grid resolution. Agreement between the free surface runs and the weak top layer models is satisfactory only if both approaches use high resolution. Comparison of numerical models with a free surface laboratory experiment shows that (1) Lagrangian-based free-surface numerical models can closely reproduce the laboratory experiments provided that sufficient numerical resolution is employed and (2) Eulerian-based codes with a weak surface layer reproduce the experiment if harmonic averaging of viscosity is used. The harmonic mean is also preferred if circular high viscosity bodies with or without a lubrication layer are considered. We conclude that modelling the free surface by a weak zero-density layer gives good results but care has to be taken in 1) handling the associated entrainment and formation of a lubrication layer and 2) choosing the appropriate averaging scheme for viscosity at rheological boundaries.

• Journal Article Type: Article
• Publication Date: 2008
• Journal: Physics of the Earth and Planetary Interiors
• Print ISSN: 0031-9201
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 171
• Pages: 198-223
• DOI: https://doi.org/10.1016/j.pepi.2008.06.028
• Keywords: Subduction, Geodynamics, Numerical modelling
• Public URL: https://durham-repository.worktribe.com/output/1532796
• Publisher URL: http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V6S-4SYTC9J-2&_user=121711&_coverDate=12%2F31%2F2008&_rdoc=19&_fmt=high&_orig=browse&_srch=doc-info(%23toc%235822%232008%23998289998%23701960%23FLA%23display%23Volume)&_cdi=5822&_sort=d&_docanchor