The intimate association of folds and faults in deformed sedimentary rocks is well-established and has led to many geometric and kinematic models of thrust-related folding. Our mechanical understanding of this geologic process is not as advanced. Since rocks are strongly anisotropic materials, it is not surprising that this parameter should be a focus of mechanical models for thrust-related folding. However, few numerical studies have addressed the role of mechanical anisotropy on the development of thrust-related folds because of the inherent difficulties. Numerical simulation of anisotropic behavior necessitates either a complex constitutive relationship or elaborate initial configurations. Unfortunately, each procedure yields a model that is very computationally-intensive. Anisotropic constitutive relationships also require specification of additional material parameters that are not particularly well-understood for most geologic materials.

In this study, methods for introducing anisotropy into finite element models are evaluated. These include both geometric anisotropy, such as simple sedimentary layering, as well as true material anisotropy via an anisotropic constitutive relationship, such as anisotropic plasticity or a "jointed material" model. Based on this evaluation of different methods, several end-member thrust-related fold types are analyzed. Initial focus is on the progressive development of detachment, fault-arrest, and fault-bend folds with respect to the role of mechanical anisotropy.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas