# Dictionary:S-wave

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A body wave in which the particle motion is perpendicular to the direction of propagation. Also called secondary wave (undae secundae), shear wave, transverse wave, rotational wave, distortional wave, equivolumnar wave, tangential wave. S-waves may be generated by an appropriate source (e.g. a vibrator), or by the incidence of P-waves on interfaces at other than normal incidence, in which case they are called converted waves. In an isotropic medium the velocity of shear waves ${\displaystyle V_{s}}$ is given by

${\displaystyle V_{s}={\sqrt {\frac {\mu }{\rho }}}={\sqrt {\frac {E}{2\rho (1+\sigma )}}}.}$

where ${\displaystyle \mu }$ is the shear modulus, ${\displaystyle \rho }$ is the density, ${\displaystyle E}$ is Young's modulus, and ${\displaystyle \sigma }$ is Poisson's ratio. S-waves have two degrees of freedom and can be polarized in various ways. See SH-wave and SV-wave. S-wave reflection data are often displayed at half the vertical scale of the comparable P-wave data to compensate roughly for the differences between S-wave and P-wave velocities; see Figure S-28. See Danbom and Domenico (1987)[1], Tatham and McCormack (1991)[2], and Garotta (2000)[3].

Figure S-28. S-wave and P-wave sections compared. (a) P-wave section; (b) S-wave section plotted at half the vertical scale used for the P-wave section. (Courtesy CGG.)