Visualizing Strain

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Strain Defined

The components of deformation of a rock body are rotation, translation, distortion, and dilation. During deformation one or more of these four components may be zero. If, for example, during deformation the rock body undergoes no distortion or no volume change, then deformation consists of either a rigid-body translation, a rigid-body rotation, or includes components of both translation and rotation. In contrast, if volume change, translation, and rotation are all zero, then deformation consists of a non-rigid body distortion or strain. Though commonly confused with each other, strain is only synonymous with deformation if there has been distortion without any volume change, translation, or rotation. In short, strain represents only one of four possible components involved in the overall deformation of a rock body where it has been transformed from its original position, size, and shape to some new location and configuration (van der Pluijm and Marshak, 1997). Strain describes the changes of points in a body relative to each other, or, in other words the distortions a body undergoes. The reference frame for strain is thus internal.

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