They can travel through solids, liquids, and gases. As the P wave travels through the rock, it stretches and compresses the rock particles. If you and a friend have ever held a jump rope between you, you probably moved the rope up and down like a whip. A secondary, or S wave moves through the earth causing the rock particles to move at right angles to the direction of the wave. Secondary waves can move through solids, but not liquids or gases.
L waves generate outward from the epicenter on the surface of the earth.
Surface waves move like waves in the ocean, causing the surface of the earth to move up and down in an eliptical motion. L waves cause the most damage because surface structures aren't made to bend and twist. A seismograph is an instrument that detects primary, secondary and surface waves. A seismologist is a scientist who studies seismic waves and earthquakes. A seismograph consists of a weight attached to a wire or a spring like a pendulum.