FLEXIBLE APPROACHES TO KINEMATIC FORWARD MODELING OF FAULT-BEND FOLDING (Invited Presentation)

Kinematic forward modeling is commonly employed in regional tectonics, earthquake hazards studies, and petroleum industry exploration efforts to constrain subsurface regions that have experienced fault-related folding. Such modeling are done because they have been shown to be useful predictors of first-order geometries in the subsurface, because they are deterministic and thus allow for imposition of specific structural interpretations where data is lacking, and because the methods are potentially fast to implement. Significant limitations exist in kinematic modeling however. The algorithms are generally simplistic and frequently result in highly generalized sections that don’t fully, or even remotely, capture the complexity of the observed deformation. Furthermore individual structures generally must be modeled, and often the generation of sequential sections must be combined with more laborious balancing methods over several time steps to more closely approximate known structural constraints.

We present flexible extensions to kinematic forward modeling algorithms of fault-bend folding that attempt to ameliorate some of these limitations. These extensions include relaxing of the constraints of fully conserved line length and layer thickness in contraction, simultaneous movement on multiple faults, and temporal and spatial variation in velocity boundaries during modeling. With these extensions it is possible to rapidly match natural examples of fault-bend folds imaged with seismic-reflection data, as well as analog and mechanical models. These extensions present their own potential problems in that the parameter space potentially greatly expands. For example, if only the final deformed state is known, then frequently multiple equivalent kinematic solutions exist. Our approach is to use natural, analog, and mechanical models to inform the plausible range of these parameters. Incorporation of aspects of the deformation path through time-dependent features, such as growth strata, internal strain within deformed blocks, and well constrained fault and fold geometries greatly narrows the parameter space. The ability to reasonably limit the parameter space is a required precursor to any useful inversion modeling scheme for fault-related folding.