Analysis of folding by superposition of strain patterns

Two methods have been developed in this paper to model the strain state and the layer geometry of folds. These methods analyse the superposition of strain patterns due to layer shortening, tangential longitudinal strain, flexural-flow and fold flattening. The first method multiplies the deformation gradients of these strain patterns to model the successive superposition of mechanisms. The second method is more general and is based on the transformation of points from the initial configuration to deformed points according to the geometrical properties of the folding mechanisms involved. This method simulates the simultaneous and successive superposition of strain patterns. Both methods generate graphic outputs that describe the strain variation through the folded layer. Another application of these methods is to attempt to find theoretical folds that fit natural or experimental folds and to perform a geometric and kinematical analysis of these folds. Knowledge of the shape of the folded layer and the cleavage pattern is the most common basic information available in natural folds that can be used to perform the analysis. Additional strain data from the folded rocks are valuable for improving knowledge of the kinematical mechanisms involved in the folding.