Secondary Wave (S-Wave)
S wave; Shear wave; Transverse wave
Secondary waves are elastic shear waves that travel through the Earth.
S waves are seismic body waves meaning they travel through the Earth’s interior. Their velocity is slower than that of P waves, and they are normally the second major phase to be observed on a seismogram, and are therefore also referred to as secondary waves. In the Earth’s crust, S wave velocities are typically 3–4 km/s. S waves are usually larger in amplitude than P waves and may cause strong shaking and/or damage. The particle motion associated with S waves is perpendicular to the direction of propagation. S waves can be subdivided into two groups: SV waves, which are recorded by seismographs on the vertical and radial components; and SH waves, which appear on the tangential component. S waves cannot propagate through liquids or gases, the knowledge of which helped lead to the discovery that the outer core was liquid.