transverse wave that occurs in an elastic medium when it is subjected to periodic shear. Shear is the change of shape, without change of volume, of a layer of the substance, produced by a pair of equal forces acting in opposite directions along the two faces of the layer. If the medium is elastic, the layer will resume its original shape after shear, adjacent layers will undergo shear, and the shifting will be propagated as a wave. The velocity (nu) of a shear wave is equal to the square root of the ratio of shear modulus (G), a constant of the medium, to density (rho) of the medium, nu = G/rho.
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