RESTORATION OF STRUCTURAL CROSS-SECTIONS

Cross-section restoration transforms deformed stratigraphic boundaries (the cross-section) into a less deformed state at an earlier time in the structural history. It is best described by transformation equatio ns which incorporate rigid translation and rotation plus deformation. These equations can be linear (affine) or non-linear. Strain is a func tion of the transformation constants, and linear transformation equati ons produce homogeneous strain. Most existing restorations use linear transformations, and many assume simple shear strain, a special case o f linear transformation. Linear transformations (such as simple shear) cannot, in general, preserve both area and continuity in cross-sectio n restoration: i.e. if area is constrained, there will be gaps and ove rlaps between different regions of the restored cross-section. If gaps and overlaps are eliminated, area cannot be constrained.Cross-section restoration can be achieved by solving a geometric boundary value pro blem using quadrilateral domains with non-linear transformations. The geometric boundary conditions are specified by knowlege of the positio n of an undeformed layer boundary and the pin line. Strain measured in the field can be incorporated as an initial condition. Discontinuitie s (faults) can be incorporated into the solution by treating them as a n internal boundary without gaps or overlaps. (C) 1997 Elsevier Scienc e Ltd.