Seismic Waves
Seismic waves provide some evedence of what might be inside the earth. The earthquake in Japan was measured be the university of Manitoba the p waves from Japan traveled right through the center of the earth. Through that we know that p waves can travel throught gas liquide and solides.
P Wave
The p wave is the smallest and the fastest wave of them all. The p wave is known to go through the entire earth, so on the other side of the earth you could feel a little bit of shaking. The reason the the p wave can do this is because the p wave can pass throught liquide solide and gas making this wave the first wave you will feel during a earthquake and does not usually cause any damage.
S Wave
The s wave is the second wave you feel it is much slower than the p wave, but it can only pass through gas and solide things so it doesn't go very far. The s wave I more dustructive than the p wave but not by much. The s wave moves like a slinky. Say you and a freind are holding a slincky and start shaking it up and down the s wave moves like that.
Surface Wave
The surface wave is the wave that casues all the dustruction with its straight forward rolling motion. It goes through every thing but liquide and gas, the surface wave is the slowest wave of all of them but is the most dustructive.
This website will show you how the waves move.
http://www.forgefx.com/casestudies/prenticehall/ph/seismic/seismic-waves-simulator.htm
http://www.forgefx.com/casestudies/prenticehall/ph/seismic/seismic-waves-simulator.htm