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The square may undergo shape change but its shape is geometrically definite such as a parallelogram. The result is DISTORTION or STRAIN or DEFORMATION although the last term encompasses all such as translation, rotation and shape change. But the shape is such that the lines that were initially straight have remained so, the lines that were initially parallel have too remained parallel even after deformation and if we implant a circle in each small square, all the ellipses that result from initial circles will have the same long axis to short axis ratio in the entire mass or body or plane. This is called HOMOGENEOUS deformation in which straight lines remain straight, parallel lines remain

parallel and the amount or magnitude of strain is uniform over the entire deformed body. True, you will notice that some lines or sets of lines have increased in length while others have shortened. This depends upon the orientation of the long and short axes of the ellipse that results from the circle and will be dealt with later. Fig to the right shows that the square is now distorted in such a manner so that its entire shape cannot be defined in any geometrical terms. However, it may be possible to break this down to smaller and smaller sizes so that finally we do obtain a shape that could justify its identification to what we might call geometrically definite. But we shall see this aspect later. You will notice that the parallel lines are no longer parallel and straight lines have lost their rectilinear and have become curved. Again you will notice that the long axis to short axis ratio of each resulting ellipse is different, what is more, the orientations of these axes are also at variance. Such strain is called HETEROGENEOUS or INHOMOGENEOUS strain. Hence in heterogeneous deformation, straight lines become curved, parallel lines become nonparallel and the amount or magnitude of strain varies across the body from one point to another point. Most natural geological deformations conform to this kind of strain since the rocks themselves are heterogeneous and resulting strains in different parts of the rock body are therefore also heterogeneous.