Flexi Says: P-waves (primary waves) are a type of longitudinal wave that is generated during an earthquake. P-waves are the fastest moving seismic waves, traveling at about 6 to 7 kilometers (about 4 miles) per second. The name "primary waves" was given because they are the first seismic waves to arrive at a seismometer following an earthquake. Like all longitudinal waves, P-waves move through matter by a compression/expansion type motion. P-waves squeeze and unsqueeze rock and other Earth materials as they travel.