second question why the slower S wave

seismic waves. One is p, one is s. p propagation in a straight line, and through a variety of substances, to spread underground, the first 4,5 km / s, and later 7km / s. s go s line, so slow, liquids and gases do not pass through. There is also a surface wave, looks like a P wave and S wave generated when the transfer (with questions surface wave and p, s the difference, I chose the later surface wave generation), transmission line at the surface (there ask why surface wave will cause great damage to the ground), a tremendous impact to the surface. The first question asked of the surface p wave band-band and near the core difference