Numerical Description of Folded Surfaces Depicted by Contour Maps

A method has been developed to describe numerically three-dimensional folded surfaces represented by structure contour maps in rectangular areas. The method uses two-dimensional surface profiles denned along radial lines emanating from the center of the map area; when combined, the two-dimensional representations provide an omnibus numerical description of the three-dimensional folded surface in the map area. Four parameters of shape are used to describe surface profiles: (1) polar slope index 1, (2) polar slope index 2, (3) marginal polar slope, and (4) polar curvature index. The description afforded by the shape parameters is sensitive to orientation as well as to shape of the fold. The shape parameters are simple, easy to compute, and readily interpreted geometrically. Use of the shape parameters allows efficient and systematic analysis of fold geometries by quantitative methods. A graphical device that facilitates study and comparison of folded surfaces by means of the shape parameters is described.