Why is it that S wave cannot pass through liquids?

Answer 1

There is an excellent animated illustration of the various type so seismic waves, and liquid surface waves, at
http://www.kettering.edu/~drussell/Demos/waves/wavemotion.html

S-waves are transverse waves, in which molecular motion is perpendicular to the direction of propagation of the wave. Inside a liquid, such motion is rapidly attentuated by viscous forces, since molecules do not have to return to the same place.