MECHANICAL FOLD DEVELOPMENT AND THE INITIATION OF TENSILE FRACTURES

Tensile failure associated with buckle folding is commonly associated to the distribution of outer arc extension but has also been observed on fold limbs. This study investigates whether tensile stresses and associated failure can be explained by the process of buckling under realistic in-situ stress conditions. A 2D plane strain finite element modeling approach is used to study single-layer buckle folds with a Maxwell visco-elastic rheology. A variety of material parameters are considered and their influence on the occurrence of tensile stresses during the various stages of deformation is analyzed. It is concluded that the buckling process determines the strain distribution within the fold layer but is not solely responsible for the occurrence of tensile stresses. In particular, tensile stresses in the limb of the fold cannot (in general) be explained by buckling. Rather, it develops due to a combination of compression and erosional unloading. The modeling results show that erosion of high permeability rocks can explain the generation of tensile stresses at significant depths (~2km) both at the crest of the fold and throughout the limb of the fold.