Primary waves are the fastest kind of waves that occur during earthquakes. They are the first to hit areas surrounding the seismic activity and can move through solid and liquid layers of the ground.
Primary waves push and pull on rock in a similar fashion to how sound waves push and pull air. Dogs can sometimes hear primary waves which is why they begin barking right before an earthquake is felt by humans. Particles that the primary wave hits move in the same or exact opposite direction as the wave is moving. Secondary waves hit following the primary waves and move things either up and down or side to side.