RELAXED KINEMATIC FAULT-BEND FOLDING CONSTRAINTS INFORMED BY MECHANICAL MODELING

Geologists are often confronted with incomplete data defining the geometry of folds and faults; however, understanding the accurate geometry and temporal evolution of geologic structures is essential to many scientific and societal applications, including petroleum and mineral exploration and production, seismic hazard assessment, carbon sequestration, and regional tectonic studies. Several modeling approaches have been developed to aid interpretation of structural geometry and evolution, which generally fall into the end-member categories: kinematic and mechanical models. Kinematic models provide geometric predictions of the relationships between fold and fault shape based upon first-order assumptions, such as conservation of cross-sectional area, yet are often too simplified to be applicable to real structures; in contrast, mechanical models investigate how rocks with defined physical properties might deform under assumed constituitive relationships and applied boundary conditions, yet are dependent on imposed geometric assumptions and assumed values for rock properties, and thus are often not essentially predictive.

We have developed a numerical approach to the kinematic fault-bend folding equations that relaxes some of the constraints of that approach in order to better accommodate variations observed in natural structures. However, by introducing more free parameters, the predictive benefit of kinematic modeling is diminished, so we aim to constrain the range of physically-reasonable parameters as narrowly as possible. We compare a large suite of forward discrete element mechanical models with the best-fitting relaxed-constraint kinematic fault-bend folding models, demonstrating that these modifications are essential to reproducing the temporal and geometric evolution of these structures. By relating the variations in fault dip, layer anisotropy, and layer strength with the parameters in the kinematic models, we are able to determine systematic relationships between these variables, defining mechanically-informed narrower ranges of likely kinematic model parameters that can be used with confidence in application to natural structures. We demonstrate in the presentation the ease of varying these parameters with an interactive forward modeling program.