Southeastern Section - 62nd Annual Meeting (20-21 March 2013)

Paper No. 11
Presentation Time: 11:35 AM


ALLISON, David T., Earth Sciences, University of South Alabama, LSCB 136, Mobile, AL 36688,

Several types of common structural geology field and/or lab problems consist of the manipulation of planes and/or lines in three-dimensional space. Often these problems can be subdivided into either solving for the plane contained by two non-parallel vectors, or the rotation of one linear vector about another. Two fundamental vector operations, the dot-product and cross-product, are efficient computational methods for solving these types of geometrical problems within spreadsheet applications, including those that operate on current tablet or smart phone operating system platforms. These computational algorithms are purely mathematical, and do not require visual interpretation of projections, or reference-plane assumptions. Traditionally these problems have been solved with stereonet projections diagrams, however, these diagrams are inconvenient and difficult to construct in most field environments- especially in the case of multi-step rotations. Stereonet projections may also suffer from accuracy problems in certain situations as compared to a computer-generated solution. Several spreadsheets are presented in this paper for organizing and then solving a variety of common structural geology problem scenarios: (1) strike and dip of a plane given two apparent dips, (2) strike and dip of a plane given three points of known elevation that lie in the plane (i.e. a three-point problems), (3) apparent dip angle along a specific azimuth direction given the strike and dip of a plane, (4) trend and plunge of the line of intersection of two non-parallel planes, (5) pre-folding attitude of a mineral lineation contained in the limb of a fold, (6) attitude of bedding in a rotated fault block given the bedding attitude in the undeformed block (7) given the planar attitudes of the S and C surfaces in a mylonite, calculate the slip direction attitude. The Microsoft Office 2010 compatible spreadsheets may be freely downloaded from the author's web site, and may be used by several spreadsheet applets that execute on the Android OS platform. By utilizing these spreadsheets the user may efficiently calculate the solution to the problems described above at the outcrop rather than waiting to process the data at base camp or classroom.
  • VectorMethods.pptx (1.9 MB)