Why do seismic waves travel faster through solids than water?

As a seismologist with a focus on the behavior of seismic waves, I can explain why seismic waves travel faster through solids than water. Seismic waves are vibrations that travel through the Earth's layers, and they are categorized into two main types: P-waves (primary waves) and S-waves (secondary waves). P-waves are the fastest and can travel through all states of matter, including solids, liquids, and gases. They are longitudinal waves that move in the same direction as the wave is propagating, causing the material they pass through to compress and expand. The speed of P-waves is influenced by the density and elasticity of the medium they are traveling through. Solids, like rocks, have a more rigid structure and higher density compared to water. This means that the particles in a solid are closer together and the intermolecular forces are stronger. As a result, when a P-wave passes through a solid, the particles can transmit the energy of the wave more efficiently and with less resistance than in water. The greater the elasticity (the ability of a material to return to its original shape after being deformed), the faster the wave can travel because the particles can push and pull against each other more effectively. In contrast, water, being a liquid, has a less rigid structure with particles that are farther apart and subject to weaker intermolecular forces. This allows the P-waves to travel through water, but the energy transfer is less efficient due to the greater distance between particles and the weaker forces holding them together, resulting in slower wave speeds. To summarize, the key factors that contribute to the faster speed of seismic waves in solids compared to water are the higher density and elasticity of solids, which allow for more efficient energy transfer and propagation of the waves.

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. It pushes and pulls the rock it moves through just like sound waves push and pull the air.