shear wave

A type of seismic wave, the S-wave, secondary wave, or shear wave, sometimes called an elastic S-wave, is one of the two main types of elastic body waves, so named because they move through the body of an object, unlike surface waves.The S-wave moves as a shear or transverse wave, so motion is perpendicular to the direction of wave propagation: S-shaped, like waves in a rope, as opposed to waves moving through a slinky, the P-wave. The wave moves through elastic mediums, and the main restoring force comes from shear effects. These waves are divergenceless and obey the continuity equation for incompressible media.
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