A sudden and violent movement, or fracture, within the Earth, followed by a resultant series of shocks. Earthquakes occur in narrow, continuous belts of activity which correspond with plate junctions; see Witter et al. (2003) GSA Bull. 115, 10. The scale of the shock of an earthquake is known as the magnitude; the most commonly used scale is the Richter scale, while the intensity of an earthquake is measured by the Mercalli scale.
Earthquake waves are of three basic types: P, primary, push waves travel from the focus by the displacement of surrounding particles and are transmitted though solids, liquids, and gases; S, secondary or shake waves travel through solids; and L, long or surface waves travel on the Earth’s surface. Computers have been used in earthquake wave analysis since the 1980s; see Tan et al. (2008) Turkish J. Earth Sci. 17. For earthquake prediction, see Brace et al. (1966) J. Geophys. Res. 71, 16 on dilatancy theory; Kuo et al. (2006) Ground Water 44, 5 on radon-222; and Chen et al. (2002) Geology 30 on older fault scarps. Rhoades et al. (2011) Acta Geophysica 59, 4, 728 investigate the efficiency of earthquake forecasting models.