Surface wave
A seismic wave that travels along Earth's surface rather than through its interior. The two principal types are Rayleigh waves and Love waves.
Rayleigh wave: A seismic surface wave whose particles move in elliptical paths within a vertical plane parallel to its direction of travel. It is one of the two principal surface-wave types, combining vertical and horizontal ground motion.
Surface-wave magnitude: An earthquake magnitude scale estimated from the amplitude and period of seismic surface waves. This magnitude measure uses the waves' recorded amplitudes to compare earthquake sizes.
Body wave: A seismic wave that travels through Earth's interior rather than being confined to its surface. Body waves pass through the interior, unlike the surface-bound waves defined here.
1906 San Francisco earthquake: A major earthquake that struck San Francisco on April 18, 1906, causing extensive damage and fires. Its seismic records and destruction illustrate the effects of large earthquake ground waves.
Love wave: A seismic surface wave that produces horizontal shear motion perpendicular to its direction of travel. It is the other principal type, shaking the ground sideways without vertical motion.
Seismology: The study of earthquakes, seismic waves, and the structure and processes of Earth. Surface waves are analyzed to measure earthquakes and probe Earth's interior.
P wave: A compressional seismic body wave in which particles move parallel to the direction of propagation. Its compressional motion and ability to cross liquids distinguish it from surface waves.
1964 Alaska earthquake: A magnitude 9.2 earthquake that struck southern Alaska on March 27, 1964. The event generated powerful, long-period ground motion across a broad region.
Seismic wave: A disturbance that carries energy through or along Earth after an earthquake or another source of seismic activity. Surface waves are one branch of seismic waves, distinguished by traveling along the ground.
Seismic tomography: A method for imaging Earth's interior from the travel times and paths of seismic waves. Surface-wave travel speeds contribute maps of variations in crust and upper-mantle structure.