Seismic Waves
Seismic waves-energy waves produced by earthquakes-permit scientists to determine the location, thickness, and properties of Earth’s internal zones. They are generated when rock masses are suddenly disturbed, such as when they break or rupture. Vibrations spread out in all directions from the source of the disturbance, traveling at different speeds through parts of Earth’s crust and interior that differ in chemical composition and physical properties. The principal categories of these waves are primary, secondary, and surface. All three types of waves are recorded on an instrument called a seismograph.
