How do S and P waves move?

As a seismologist with extensive experience in the study of seismic waves, I can provide a detailed explanation of how S and P waves move. P waves, also known as primary waves, are the fastest type of seismic body wave. They are characterized by a compressional motion where particles of the medium through which they travel move back and forth in the same direction as the wave's propagation. This is why P waves can travel through all states of matter: solids, liquids, and gases. Their speed can vary depending on the medium, but they generally move faster through denser materials like the Earth's mantle. S waves, or secondary waves, are slower than P waves and follow shortly after. Unlike P waves, S waves are transverse in nature, meaning the particle motion is perpendicular to the direction of wave propagation. They can only travel through solids because the particle motion requires a rigid medium to maintain the wave's shape and energy. S waves cannot move through liquids or gases, which lack the rigidity necessary for this type of wave motion. In summary, P waves move through the Earth by compressing and expanding materials in the direction of the wave's travel, allowing them to pass through all states of matter. S waves, on the other hand, move by shearing the material, which is only possible in solids.

These waves are of a higher frequency than surface waves. The first kind of body wave is the P wave or primary wave. This is the fastest kind of seismic wave, and, consequently, the first to 'arrive' at a seismic station. The P wave can move through solid rock and fluids, like water or the liquid layers of the earth.