Strain localisation in mechanically layered rocks beneath detachment zones: insights from numerical modelling.

Laetitia Le Pourhiet 1 Benjamin Huet 2 Loic Labrousse 1 Kouakou F. E. Yao 3 Philippe Agard 1 Laurent Jolivet 4
1 iSTeP - Institut des Sciences de la Terre de Paris
2 Department for Geodynamics and Sedimentology [Vienne]
3 GEOSCIENCES - Centre de Géosciences
4 ISTO - Institut des Sciences de la Terre d'Orléans - UMR7327
Abstract : Fully dynamic numerical simulations have been designed in order to asses how the orientation of mechanical layering in rocks controls the orientation of shear bands and the depth of penetration of strain in the footwall of detachment zones. Two parametric studies are presented. In the first one, the influence of stratification orientation on the occurrence and mode of strain localisation is tested. The second parametric study shows that results are length-scale independent and that orientation of shear bands is not sensitive to the viscosity contrast or the strain rate. Based on the results, a conceptual model for strain localisation under detachment faults is presented. In the early stages, strain localisation occurs at slow rates by viscous shear instabilities but as the layered media is exhumed, the temperature drops and the strong layers start yielding plastically, forming shear bands and localising strain at the top of the shear zone. Once strain localisation has occured, the deformation in the shear band becomes extremely penetrative but the strength cannot drop since the shear zone has a finite thickness.
Keywords : detachment fault shear bands strain dynamic numerical simulation mechanical layering
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Laetitia Le Pourhiet, Benjamin Huet, Loic Labrousse, Kouakou F. E. Yao, Philippe Agard, et al.. Strain localisation in mechanically layered rocks beneath detachment zones: insights from numerical modelling.. Solid Earth, European Geosciences Union, 2013, 4, pp.135-152. ⟨10.5194/se-4-135-2013⟩. ⟨hal-00822400⟩

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