The numerical sandbox: Comparison of model results for a shortening and an extension experiment
Susanne J. H. Buiter, Andrey Yu. Babeyko, Susan Ellis, Taras V. Gerya, Boris J. P. Kaus, Antje Kellner, Guido Schreurs, Yasuhiro Yamada, 2006. "The numerical sandbox: Comparison of model results for a shortening and an extension experiment", Analogue and Numerical Modelling of Crustal-Scale Processes, S. J. H. Buiter, G. Schreurs
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We report results of a study comparing numerical models of sandbox-type experiments. Two experimental designs were examined: (1) A brittle shortening experiment in which a thrust wedge is built in material of alternating frictional strength; and (2) an extension experiment in which a weak, basal viscous layer affects normal fault localization and propagation in overlying brittle materials. Eight different numerical codes, both commereiai and academic, were tested against each other. Our results show that: (1) The overall evolution of all numerical codes is broadly similar. (2) Shortening is accommodated by in-sequence forward propagation of thrusts. The surface slope of the thrust wedge is within the stable field predicted by critical taper theory. (3) Details of thrust spacing, dip angle and number of thrusts vary between different codes for the shortening experiment. (4) Shear zones initiate at the velocity discontinuity in the extension experiment. The asymmetric evolution of the models is similar for all numerical codes. (5) Resolution affects strain localization and the number of shear zones that develop in strain-softening brittle material. (6) The variability between numerical codes is greater for the shortening than the extension experiment.
Comparison to equivalent analogue experiments shows that the overall dynamic evolution of the numerical and analogue models is similar, in spite of the difficulty of achieving an exact representation of the analogue conditions with a numerical model. We find that the degree of variability between individual numerical results is about the same as between individual analogue models. Differences among and between numerical and analogue results are found in predictions of location, spacing and dip angle of shear zones. Our results show that numerical models using different solution techniques can to first order successfully reproduce structures observed in analogue sandbox experiments. The comparisons serve to highlight robust features in tectonic modelling of thrust wedges and brittle-viscous extension.
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Analogue and Numerical Modelling of Crustal-Scale Processes
The crust of the Earth records the deformational processes of the inner Earth and the influence of the overlying atmosphere. The state of the Earth’s crust at any time is therefore the result of internal and external processes, which occur on different time and spatial scales. In recent years important steps forward in the understanding of such complex processes have been made by integrating theory and observations with experimental and computer models. This volume presents state-of-the-art analogue and numerical models of processes that alter the Earth’s crust. It shows the application of models in a broad range of geological problems with careful documentation of the modelling approach used. This volume contains contributions on analogue and numerical sandbox models, models of orogenic processes, models of sedimentary basins, models of surface processes and deformation, and models of faults and fluid flow.