Shape and structure of (analogue models of) refolded layers

The visualisation of the intricate three-dimensional shapes that arise in non-coaxial refolding is an ongoing problem in the study of multiply deformed terrains. Such complex forms also allow space for subjective interpretation of folding sequences. Analogue models offer a solution to the problem of visualisation because the entire surface of a refolded layer can be examined. In addition, analogue models may permit a quantitative geometric study by digitising models in three dimensions. This paper will examine a method for geometric analysis of multiply folded surfaces. We used the results of analogue experiments with paraffin wax where pre-formed single layer folds were deformed to produce dome-basin and dome-crescent-mushroom interference patterns. The surfaces of buckled layers in these analogue models were digitised to produce virtual models from which accurate attitude measurements of layers and fold hinges were made. To achieve three-dimensional digitising we developed an optical triangulation system based on structured light measurement by the double-scan technique. We applied standard analytical tools used by structural geologists for the analysis of the obtained data and we compared experimental structures with natural examples.