Introduction To Concepts of Two-Dimensional Strain and Their Application With the Use of Card-Deck Models

Abstract

In the first course in structural geology it is important to introduce the fundamental concepts of strain, but there are difficulties in doing so from a predominantly analytical point of view. The use of card-deck models in illustrating two-dimensional strain can serve as a bridge between the visual, but qualitative, and the mathematical aspects. By homogeneously shearing a card deck on which a circle has been drawn, the geometrical properties of the strained state can be systematically investigated, including such features as the principal axes of strain, lines of no finite longitudinal strain, the first strain invariant, the rotational component of strain, and the reciprocal strain ellipse. With both circles and ellipses, in various combinations and orientations, it is possible to examine the geometry of superimposed strains. By various graphical plots the progressive development of the finite strain ellipse can be followed, and the idea of the infinitesimal strain ellipse introduced. Many geological st...