Primary waves, also known as P-waves, are a type of seismic wave that is characterized by their longitudinal motion. They are the first waves to arrive at seismic stations after an earthquake because they travel faster than any other type of seismic wave. P-waves can move through all states of matter: solids, liquids, and gases, which makes them particularly useful in the study of Earth's interior structure. As they propagate, P-waves cause particles of the medium through which they travel to oscillate back and forth in the same direction as the wave's movement, resulting in areas of compression and rarefaction. read more >>

Primary waves are alternatingly compressional and extensional, and cause the rocks they pass through to change in volume. These waves are the fastest traveling seismic waves and can travel through solids, liquids, and gases. Also called P wave. See Note at earthquake.read more >>