Why do P waves travel faster?

As a seismologist with extensive experience in the study of seismic waves, I can explain why P-waves travel faster than S-waves. P-waves, also known as primary waves, are a type of elastic wave that can travel through solids, liquids, and gases. They are longitudinal waves, meaning that the particle motion is in the same direction as the wave propagation. P-waves are able to compress and rarefy the material they pass through, which allows them to travel through the Earth's interior with less resistance and at higher speeds. On the other hand, S-waves, or secondary waves, are transverse waves that can only travel through solids. The particle motion for S-waves is perpendicular to the direction of wave propagation. Because they cannot pass through liquids or gases, and because the shearing motion they induce is more resistant than the compression and rarefaction of P-waves, S-waves travel more slowly. The speed difference between P-waves and S-waves is also why P-waves are typically the first to be detected by seismographs during an earthquake. This speed difference is crucial for earthquake early warning systems, as it provides a brief window of time to prepare for the more destructive S-waves that follow.

P-waves and S-waves are body waves that propagate through the planet. P-waves travel 60% faster than S-waves on average, because the interior of the Earth does not react the same way to both of them. P-waves are compression waves that apply a force in the direction of propagation.