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.
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