I am, however, very familiar with sound waves in materials. Part of my dissertation dealt with investigating sound waves in materials using a type of laser scattering - called Brillouin Scattering. Due to the thermal motion of the atoms in a medium, there are always sound waves. Light can interact with these waves and scatter off. The scattered light carries with it information about the energy of the waves, from which the interaction strength and sound velocity can be calculated.
Pressure waves are stronger than shear waves.
Think about the atomic picture. It is much easier to push atoms together than it is to pull them sideways. Pressure waves can propagate from one medium to another. Shear waves have a very hard time doing that. So, when seismic waves are detected through the Earth on the opposite side, the shear waves don't survive the transit and only pressure waves are detected.