TEACHING DISPLACEMENT CONCEPTS USING COMPUTER PROGRAMS

A proper understanding of structural geology requires the use of simple continuum mechanics to analyze geological structures. The idealizations of stress and strain are particularly hard concepts for students to grasp, chiefly because it is difficult to watch progressive deformation. Computer programs are ideally suited for this type of visualization. Simple two-dimensional programs may be tied directly to straightforward mathematical operations, so students can both find analytical solutions and watch the process occur (as well as know the correct answer).

The concepts of finite strain and strain history are addressed through the visualization of a progressively deforming box. The rotation and extension or shortening of material lines can be studied, the displacement of material points can be traced, and the stresses acting on the deforming box can be plotted. One may also use other programs to examine the formation of fabric by plotting out the rotation and translation of rigid clasts in a homogeneously deforming matrix. Any combination of pure and simple shear can be used, and the effect of clast aspect ratio and initial orientation on clast rotation during deformation may be studied. Because strain does not always accumulate in one episode of deformation, other programs allow multiple deformations to be superimposed on a single block.

While two-dimensional deformation is important to understand and visualize, real geological deformation is generally three-dimensional. Using the same framework as for two-dimensional analysis, computer programs can provide an efficient way to calculate three-dimensional deformation. One program calculates the instantaneous and finite strain parameters associated with deformation, as well as rotation of material lines and planes. This approach provides a conceptual model for styles of three-dimensional deformation (flattening and constriction).