The waves are the fastest seismic waves and are the first to be detected once an earthquake has occurred. These waves travel through the earth's interior many times faster than the speed of a jet airplane, taking only a few minutes to travel across the earth. The waves are the second-fastest seismic waves and the second type to be detected once an earthquake has occurred. Although S-waves are slower than P-waves, they still travel fast, over half the speed of P-waves, moving at thousands of kilometers per hour through the earth's crust and mantle. P-waves are predominantly waves. S-waves are waves (though that is not what the S stands for). S-waves can travel only through , because only solids have rigidity. S-waves cannot travel through or gases.