(c) Homogeneous subareas due to kink or chevron folding. (b) Systematic variation in layer orientation measurements. (a) Synthetic homogeneous set of strike and dip measurements. At a later stage it became clear that the folds were in fact non-cylindrical, with curved hinge lines, requiring modification of earlier models.įig 3, Synthetic structural data sets showing different degree of homogeneity. This model made it possible to project folds onto cross-sections, and impressive sections or geometric models were created. For example, when the Alps were mapped in great detail early in the twentieth century, their major fold structures were generally considered to be cylindrical, which means that fold axes were considered to be straight lines.
Our data will always be incomplete at some level, and our minds tend to search for geometric models when analyzing geologic information. Nevertheless, it may be necessary to make geometric interpretations of partly exposed structures. In most cases, however, natural surfaces are too irregular to be described accurately by simple vector functions, or it may be impossible to map faults or folded layers to the extent required for mathematical description. Shapes and geometric features may be described by mathematical functions, for instance by use of vector functions.
Orientations of linear and planar structures are perhaps the most common type of structural data.
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