The location of the rupture determines the focus of the earthquake, the precise point where the energy waves are generated. The epicenter is the point on the Earth's surface directly above the focus point. The release of energy during an earthquake generates waves. There are two types of seismic waves - body waves and surface waves.
Body waves are transmitted through the earth, surface waves occur only on the surface of the ground.
P-waves can travel through any type of material. S is slower than P and can only travel through solids. These are also called shear waves because they generate a shearing stress. These produce rolling motions of the ground surface and are much slower than body waves. Each is valid for a particular frequency range and type of seismic signal.