Why do seismic waves travel faster through a solid rock than through water?

We are talking about the seisimc waves in an earthquake. The difference in the speed of travel of the two waves has to do with what has to happen to the medium (the ground or the earth) to transmit the energy of the seismic wave. Let's look. The P wave is a longitudinal wave or a compression wave. The force is applied in the direction that the wave is traveling. The ground must move in that direction. Ground or earth is pretty incompressible, so the energy is transferred pretty quickly. In the S wave, the medium is displaced in a transverse (up and down - compared to the line of travel) way, and the medium must shear or "move away" from the material right next to it to cause the shear and transmit the wave. This takes more time, and this is why the S wave moves more slowly than the P wave in seismic events. Need a link to seismic waves? You got it. Wikipedia has a good article, and the pictures are worth the trip over to view them.