a transverse elastic wave in a solid. In a shear wave, the particle motion is perpendicular to the direction of propagation of the wave, and the propagated disturbance is a shearing strain. The phase velocity of a shear wave is equal to where G is the shear modulus of the material and ρ is the density of the material. For most solids, the velocity is between 1.7 × 10⁵ and 3.5 × 10⁵ cm/sec. In anisotropic solids (crystals), shear waves can propagate only in certain directions, and their phase velocity depends on the direction. At hypersonic frequencies of ~10⁹ hertz or higher, shear waves can also exist in a fluid, because fluids exhibit a shear modulus in this frequency range.