Benchmarking numerical models of brittle thrust wedges
Résumé
We report quantitative results from three brittle thrust wedge experiments, comparing numerical results
directly with each other and with corresponding analogue results. We first test whether the participating
codes reproduce predictions from analytical critical taper theory. Eleven codes pass the stable wedge
test, showing negligible internal deformation and maintaining the initial surface slope upon horizontal
translation over a frictional interface. Eight codes participated in the unstable wedge test that examines
the evolution of a wedge by thrust formation from a subcritical state to the critical taper geometry. The
critical taper is recovered, but the models show two deformation modes characterised by either mainly
forward dipping thrusts or a series of thrust pop-ups. We speculate that the two modes are caused by
differences in effective basal boundary friction related to different algorithms for modelling boundary
friction. The third experiment examines stacking of forward thrusts that are translated upward along a
backward thrust. The results of the seven codes that run this experiment show variability in deformation
style, number of thrusts, thrust dip angles and surface slope. Overall, our experiments show that nu-
merical models run with different numerical techniques can successfully simulate laboratory brittle
thrust wedge models at the cm-scale. In more detail, however, we find that it is challenging to reproduce
sandbox-type setups numerically, because of frictional boundary conditions and velocity discontinuities.
We recommend that future numerical-analogue comparisons use simple boundary conditions and that
the numerical Earth Science community de fines a plasticity test to resolve the variability in model shear
zones