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Analogue and Numerical Sandbox Models |
1 Centre for Geodynamics, Geological Survey of Norway, 7491 Trondheim, Norway susanne.buiter{at}ngu.no
2 GeoForschungsZentrum Potsdam, Telegrafenberg, 14473 Potsdam, Germany
3 Institute of Geological and Nuclear Sciences, P.O. Box 30368, Lower Hutt, New Zealand
4 Swiss Federal Institute of Technology, Sonneggstrasse 5, 8092 Zürich, Switzerland
5 Department of Earth Sciences, University of Southern California, Los Angeles, USA
6 Institute of Geological Sciences, University of Bern, Baltzerstrasse 1-3, 3012 Bern, Switzerland
7 Department of Civil and Earth Resources Engineering, Kyoto University, Kyoto 606-5801, Japan
8 Institut für Meteorologie und Geophysik, J.W. Goethe Universität Frankfurt, Germany
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 commercial 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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  G. Schreurs, S. J. H. Buiter, D. Boutelier, G. Corti, E. Costa, A. R. Cruden, J.-M. Daniel, S. Hoth, H. A. Koyi, N. Kukowski, et al. Analogue benchmarks of shortening and extension experiments Geological Society, London, Special Publications, 2006; 253: 1 - 27. [Abstract] [PDF]
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