Influence of erosional unloading on the state of stress for low amplitude single-layer buckle folds - implications for tensile fracture occurence

The existence of fractures associated to buckle folds is related to the strain distribution of the fold. The erosional unloading process can amplify the remnant strain in the folded layer. Two-dimensional plane strain Finite Element Analysis (FEA) is used to investigate the influence of the erosional unloading step on both the evolution of the state of stress and the associated failure patterns in low amplitude buckle folds. Sensitivity analyses on different input parameters, including viscosity, shortening ratio, and overburden pressure, are performed. Based on the simulation results, tensile stress can be initiated both in the crest and in the limb of low amplitude buckle folds in high permeability models during the elastic erosional unloading process. Tensile failure can be initiated perpendicular to the bedding in the top of the fold crest. The type of fracture in the limb depends on the strength of the rock. Tensile failure is initiated in the fold limb more likely for strong rocks while shear failure is initiated more likely for weak rocks. The orientation of both the stresses and the subsequent fractures in low amplitude folds is not affected by the erosional unloading process. In summary, the initiation of both the tensile stress and the subsequent fractures depends on rock properties and strain history.