Deformation of a rock body occurs in response to a force, and involves (a) a rotation, (b) a translation, (c) a distortion or strain, and (d) a volume change or dilation (Davis and Reynolds, 1996; van der Pluijm and Marshak, 1997). However, during deformation of a rock body 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. Hence, though commonly confused with each other, strain is only synonymous with deformation if there has not been any volume change, translation, or rotation. In short, strain represents only one of four possible components involved in the overall transformation of a body of rock from its original position, size, and shape to some new location and configuration (van der Pluijm and Marshak, 1997).
Show Me Dilation or Volume Change