<P> which is simply the wave equation applied to the curl of u with a velocity β (\ displaystyle \ beta) satisfying </P> <Dl> <Dd> β 2 = μ ρ (\ displaystyle \ beta ^ (2) = (\ frac (\ mu) (\ rho))) </Dd> </Dl> <Dd> β 2 = μ ρ (\ displaystyle \ beta ^ (2) = (\ frac (\ mu) (\ rho))) </Dd> <P> This describes S - wave propagation . Taking the divergence of seismic wave equation in homogeneous media, instead of the curl, yields an equation describing P - wave propagation . The steady - state SH waves are defined by the Helmholtz equation </P>

S waves are also known as transverse waves