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'S' waves arrive at the seismograph after the 'P' waves. Is this because they do not travel in a straight line, or because they will not pass through a liquid?
S waves are called S for 2 reasons: they are the Second wave to arrive (after the Primary wave), and they travel through solid materials (like most of the earth's interior) with a Shearing motion. This second reason (they are Shear waves) is due to the way they propagate.
Imagine a slinky (the coiled up kid's toy): you can stretch and compress it. Primary waves use this motion. So do sound waves, which is why your eardrum works and you can hear sounds.
Now tie a rope to a wall and shake it up and down: if you follow the actual motion of any individual piece of rope it is also up and down. This is like the Shear waves. Yes, the energy follows a longer path, and should therefore take longer to transit the same distance.
It is also true that S waves will not pass through liquids, but I don't think that this affects their velocity through a solid. Analysis of seismic waves point to an "S wave shadow zone." What this indicates is that there are portions of the earth's interior which may not be solid (at least as we understand the term here on the surface).
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