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 modelsinto a unified framework. Fault-parallel flow, inclined shear, classical fault-bend folding (flexural-slip fault bendfolding), and backlimb trishear are combined within this methodology. Hanging-wall particle velocities are computedbased on the asymmetry of the axial trace relative to the bisector of each fault bend. A backlimb trishearzone for smoothing deformation over sharp fault bends can be added to produce a curved shape in the resultingfolds. Validation against analog physical experiments and natural examples demonstrates a strong agreement, accuratelycapturing the geometry of natural folds. By incorporating asymmetry angles and backlimb trishear apicalangles, 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 enablingindependent 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 afoundation for integration into more advanced software. Its computational efficiency and reversibility make itparticularly well-suited for iterative model adjustments to fit real data. This integration of fault-bend fold modelsrepresents a significant advancement, offering a robust framework for simulating complex geological structuresconsistent with seismic profiles, well data, and field observations. Moreover, by adjusting the slip direction, themodel can be adapted to accommodate both reverse and normal faulting, making it applicable to a wide range ofgeological scenarios. Strain in the models can be effectively tracked by embedding objects of known shape, suchas circles or a regular grid, in the undeformed state.