Pitfalls and procedures for determining fabric orientations in non-oriented bore core

Given three differently oriented boreholes intersecting the same structural fabric, the absolute orientation of that fabric can be calculated even when the azimuthal orientation of the core is unknown. The true fabric is defined by the common intersection of at least three small circles, each of which represents the cone of possible orientations for a core segment. Potential pitfalls associated with automating this simple concept for the analysis of large data sets on a microcomputer include incorporating the effect of errors associated with measuring the fabric in the core, and the nature of the intersection between pairs of small circles. These pitfalls can he overcome by following a procedure which uses a combination of minimum angular dispersion to select representative solutions, and eigenvector calculations to define the mean fabric and its associated error envelope.