Role of Faults and Layer Interfaces on the Spatial Variation Stress Regime in Basins: Inference from Numerical Modelling

W. Sassi and J.-L. Faure

Stress regime variation can to some extent be investigated theoretically using geomechanical considerations as demonstrated by the slip-line calculations of Hafner (1951), the work of Sandford (1959) and others who provided studies of stress trajectories and distributions for simple geological situations. In this way more complex problems can nowadays be treated using numerical methods to solve stress equilibrium equations. Numerical modelling approaches have proved to be useful to study the formation of tectonic faulting in terms of localisation of deformation with non-linear rheology. However, there is a strong interest in modelling more complex situations which account for the heterogeneous rock properties and the presence of faults in the analysis of basin deformation problems.

The aim of this contribution is to demonstrate that geomechanic models can be useful in studies of stress distribution in complex systems despite their well-known intrinsic limitations when dealing with basin-scale structural interpretation problems. The first example describe the stress regime variation around a reactivated planar default (e.g. a Griffith's crack). The second one is a simulation of a thrust propagation sand-box experiment. In the first two cases, homogeneous rock properties are considered. In the last two models the presence of layer interfaces and contrasted rock mechanical properties are also taken into account. The third model is an example of thin-skinned compression, and the last one illustrates folding of a multilayered sequence induced by basement uplift. For ach problem, the interpretation of the results is based on the analysis of the computed stress tensors in terms of stress regime. The contour maps of the Wallace-Bott stress ratio is proposed to provide a refined geological interpretation of the results. It is shown that this representation of the state of stress is an important aid for the interpretation of three dimensional problems. It gives complementary information to the usually reported plots of solution variables such as magnitudes of maximum shear stresses, Von-Mises stresses or equivalent plastic strain.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California