A review of velocity fields in fault bend folding kinematic models: General algorithm for computational application

Abstract

This study presents a comprehensive approach to fault-related folding by integrating multiple kinematic models into a unified framework. Fault-parallel flow, inclined shear, classical fault-bend folding (flexural-slip fault bend folding), and backlimb trishear are combined within this methodology. Hanging-wall particle velocities are computed based on the asymmetry of the axial trace relative to the bisector of each fault bend. A backlimb trishear zone for smoothing deformation over sharp fault bends can be added to produce a curved shape in the resulting folds. Validation against analog physical experiments and natural examples demonstrates a strong agreement, accurately capturing the geometry of natural folds. By incorporating asymmetry angles and backlimb trishear apical angles, the model successfully reproduces complex structures, including folds with progressive limb rotation. Additionally, it enhances classical fault-bend folding, inclined shear, and fault-parallel flow models by enabling independent balancing of each fault bend, facilitating the development of curved and geologically realistic folds. Implemented in Python, the proposed algorithm allows users to test it on simple fold structures, serving as a foundation for integration into more advanced software. Its computational efficiency and reversibility make it particularly well-suited for iterative model adjustments to fit real data. This integration of fault-bend fold models represents a significant advancement, offering a robust framework for simulating complex geological structures consistent with seismic profiles, well data, and field observations. Moreover, by adjusting the slip direction, the model can be adapted to accommodate both reverse and normal faulting, making it applicable to a wide range of geological scenarios. Strain in the models can be effectively tracked by embedding objects of known shape, such as circles or a regular grid, in the undeformed state.