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Incorporating Layer Thickening and Thinning Into Kinematic Modeling of Fault-Related Folding


When balancing a cross section in an area that has been deformed by fault-related folding, it is common to employ several restoration methods, such as flexural slip, inclined shear, rotation, translation and decompaction. The choice of which to use and when during the process depends on the deformation that is thought to have occurred. Even with modern balancing software this is often a time-consuming process, and it is particularly arduous to combine methods associated with one time of deformation. Kinematic forward modeling of fault-related folding allows for easy development of balanced models over multiple time steps, yet current kinematic modeling still suffers from difficulties incorporating deformation not directly associated with displacements over bends in faults or propagating fault tips. Presented here is an approach that incorporates layer thickening and thinning during deformation associated with fault-related folding. We employ defined loci of thickening and thinning at each times step with a smoothing operator that distributes layer thickness changes across a layer and allows the other layers to respond to this additional strain while maintaining cross sectional area. At each time step changes in area of the layer due to shortening or extension are balanced by area changes due to thickening or thinning across the layer. This is done simultaneously with the other fault-related folding mechanisms modeled, such as fault-bend folding. If compaction is included in the model, conservation of mass is maintained, but not area. With this approach very realistic models can be generated in areas that normally are a challenge to model, such as mobile shale structures and some salt structures. In these cases the layer which deforms with thickness changes flows, and boundaries to the layer are discontinuities (in essence faults parallel to the layer boundary). Hybrid models of detachment folds which have thickening of an incompetent core, plus some internal duplexing, can likewise be modeled. Thickness changes of multiple layers can also be modeled in order to mimic penetrative strain that deviates from idealized, flexural-slip-dominated fault-bend folds. This approach greatly expands the ability to model realistic fault-related folds. It allows interpretations to be validated more easily, and provides insight into the evolution of structures, particularly when sedimentation and compaction are included in the forward modeling.