There are 2 types of seismic waves:      P-wave. It is a longitudinal wave.       S-wave. It is a transverse wave.    Seismic waves are detected by seismograph.    P-wave travels slightly faster than S-wave. It travels through the solid and liquid parts of the Earth.    S-wave travels only through the solid part of the Earth.   The diagram above shows the paths P and S-waves travel through the Earth. The paths curve       because they go through different densities.    P and S-waves reveal the Earth's structure as they travel and refract through it.