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Solid Earth An interactive open-access journal of the European Geosciences Union

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Solid Earth, 6, 533-552, 2015
https://doi.org/10.5194/se-6-533-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
21 May 2015
Stress field sensitivity analysis in a sedimentary sequence of the Alpine foreland, northern Switzerland
T. Hergert1,*, O. Heidbach2, K. Reiter3,2,*, S. B. Giger4, and P. Marschall4 1Karlsruhe Institute of Technology, Institute of Applied Geosciences, Adenauerring 20b, 76131 Karlsruhe, Germany
2GFZ German Research Centre for Geosciences, Section 2.6 Seismic Hazard and Stress Field, Telegrafenberg, 14473 Potsdam, Germany
3University of Potsdam, Inst. of Earth and Environmental Science, Karl-Liebknecht-Str. 24–25, 14476 Potsdam-Golm, Germany
4NAGRA, National Cooperative for the Disposal of Radioactive Waste, 5430 Wettingen, Switzerland
*now at: TU Darmstadt, Institute of Applied Geosciences, Schnittspahnstr. 9, 64287 Darmstadt, Germany
Abstract. The stress field at depth is a relevant parameter for the design of subsurface constructions and reservoir management. Yet the distortion of the regional stress field due to local-scale features such as sedimentary and tectonic structures or topography is often poorly constrained. We conduct a stress sensitivity analysis using 3-D numerical geomechanical modelling with an elasto-plastic material law to explore the impact of such site-specific features on the stress field in a sedimentary sequence of the Swiss Alpine foreland. The model's dimensions are 14 × 14 × 3 km3 and it contains 10 units with different mechanical properties, intersected by two regional fault zones. An initial stress state is established involving a semi-empirical relationship between the ratio of horizontal to vertical stress and the overconsolidation ratio of argillaceous sediments. The model results indicate that local topography can affect the stress field significantly to depths greater than the relief contrasts at the surface, especially in conjunction with horizontal tectonic loading. The complexity and frictional properties of faults are also relevant. The greatest variability of the stress field arises across the different sedimentary units. Stress magnitudes and stress anisotropy are much larger in stiffer formations such as massive limestones than in softer argillaceous formations. The stiffer formations essentially carry the load of the far-field forces and are therefore more sensitive to changes of the boundary conditions. This general characteristic of stress distribution in the stiff and soft formations is broadly maintained also with progressive loading towards the plastic limit. The stress field in argillaceous sediments within a stack of formations with strongly contrasting mechanical properties like in the Alpine foreland appears to be relatively insensitive to changes in the tectonic boundary conditions and is largely controlled by the maximum stiffness contrast with respect to the load-bearing formations.

Citation: Hergert, T., Heidbach, O., Reiter, K., Giger, S. B., and Marschall, P.: Stress field sensitivity analysis in a sedimentary sequence of the Alpine foreland, northern Switzerland, Solid Earth, 6, 533-552, https://doi.org/10.5194/se-6-533-2015, 2015.
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Short summary
A numerical model integrating the structure and mechanical properties of a sedimentary sequence in the Alpine foreland is presented to show that topography, tectonic faults and, most of all, spatialy variable rock properties affect the state of stress at depth. The tectonic forces acting on the sequence are primarily taken up by the stiff rock units leaving the weaker units in a stress shadow.
A numerical model integrating the structure and mechanical properties of a sedimentary sequence...
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