Role of faults and layer interfaces on the spatial variation of stress regimes in basins: inferences from numerical modelling

• Published in: Tectonophysics Vol. 266; no. 1; pp. 101 - 119
• Main Authors: Sassi, William, Faure, Jean-Luc
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.12.1996
• Subjects: boundary conditions; fault; fracture; kinematics; pre-existing structures; scale-dependent processes; stress deviations; stress orientation; stress regime; stress deviations; stress orientation; fault; stress regime; pre-existing structures; kinematics; boundary conditions; scale-dependent processes; fracture
• ISSN: 0040-1951; 1879-3266
• DOI: 10.1016/S0040-1951(96)00185-0

The spatial variation of the computed state of stress is studied in a series of numerically solved boundary-value problems of basin-scale deformation. These numerical experiments illustrate simple situations of decollement tectonism under compression. The study focuses on the local variation of the state of stress in a sedimentary overburden where major discontinuities such as large-scale faults and layer interfaces are present. The states of stress are computed using either the distinct element method or the finite element method. Classic elasto-plasticity laws are used for the behaviour of the continuum, and the discontinuities are modelled as Coulomb contact surfaces. A geologic interpretation of the numerical experiments is proposed to highlight the role played by major structural discontinuities in the local variations of the stress regime. The models are two-dimensional in space and assume plane strain, but the full three-dimensional stress-strain constitutive relation is used. Therefore, the stress regime variations can be represented by constructing the contour map of the Wallace-Bott stress ratio. This simple technique, together with the construction of diagrams of principal stress magnitude across the model, enables us to rapidly examine the stress-field pattern and further discuss the deformation modes of faulting and fracturing, which may take place at a small scale. We have found that the local variations of the stress tensor are in good agreement with common geologic interpretation of brittle deformations in foreland and thrust systems. We demonstrate how the presence of layer interface and the difference in mechanical properties of formation lithology may strongly affect the variation of stress in space. This modelling approach has important issues when interpreting well tests to gain access to in-situ stresses.