| Abstract: | Finite-element analysis has been used to simulate the progressive development of folds in a single layer of higher viscosity embedded in a matrix of lower viscosity and subjected to layer-parallel compression. In contrast with other studies of the problem, the layer is given an initial deflection which is not a periodic function of distance along the layer, but is instead localized and bell-shaped. The object is to see whether developing buckle folds will become periodic of their own accord.Two models have been studied, both with viscosity ratios of 10 : 1 between layer and matrix, and both with initial deflections of the same amplitude. In Model 1, however, the initial deflection has a greater span than in Model 2. During progressive deformation of the models, the initial deflections amplify, becoming buckle folds. The spans converge toward the same value, but the deflection in Model 1 amplifies faster than in Model 2. No new folds appear in Model 1, but in Model 2 new synclines appear to either side of the initial antiformal deflection. The zone of folding therefore propagates along the layering.The rate of propagation in the finite-element models is not as great as in corresponding models made from physical materials. It is suggested that this discrepancy may be due to cumulative systematic errors in the numerical method, which, in its present form, may not be entirely suitable for treating problems of instability and propagation during geological deformation. |
