Simulation of Large-Scale Thrust Faulting and Folding of Sedimentary Rocks Via the Extended Finite Element Method

Folds are geologic features commonly observed along thrust fronts where large deformation occurs and complex stress states prevail. In this paper we use two-dimensional quasi-static extended finite element modeling to simulate fault-related folding in geologic structures. The mechanical model considers the combined effects of bulk plasticity, frictional sliding on the fault, and finite deformation, including finite stretching and large rotation of a solid continuum. In contrast to standard finite element formulation, the proposed approach allows the geologic fault to propagate through and traverse the interior of the finite elements in a fixed Lagrangian grid. The advantage of the approach is that faulting can be simulated without remeshing.

The proposed finite element formulation imposes the frictional contact constraint via the penalty method enforced in the current configuration. The algorithm for bulk deformation follows the framework of multiplicative plasticity, in which the deformation gradient is decomposed in product form into elastic and inelastic parts. Numerical integration is done implicitly using classical return mapping algorithm of computational plasticity. Through numerical examples, we demonstrate how the proposed extended finite element model may be used to simulate thrusting of an oblique fault, as well as quantify the effect of fault movement on the geometry and fracture density of the resulting fold.