ABSTRACT
This chapter discusses the relationship between faults and folds in individual structures and, more generally, in “fold-and-thrust belts.” It was seen at the end of Chapter 4 that faults were needed to connect décollement levels. However, faults and folds were long considered to be mechanically incompatible. It was thought that these two structure types resulted from different modes of deformation, namely brittle tectonics and ductile tectonics. The underlying idea was that the confinement conditions on the one hand and the rate of deformation on the other were very different in each of these cases. By referring to earthquakes, which we are able to feel and observe, the development of a fault was understood as a rapid process under weak confinement. Conversely, the development of a fold was considered to be a slow process under strong confinement. Thus, a fault would only appear later during a tectonic process, for example after an erosion episode which would reduce the confinement. These theoretical considerations have been contradicted by the observation that certain structures could only be understood by accepting that faulting and folding were closely related in time and space.
