(1) A quantity characteristic of the total energy released by an earthquake, as contrasted with intensity, which describes its effects at a particular place. A number of earthquake magnitude scales exist, including local (or Richter) magnitude, body wave magnitude, surface wave magnitude, moment magnitude, and coda magnitude. As a general rule, an increase of one magnitude unit corresponds to ten times greater ground motion, an increase of two magnitude units corresponds to 100 times greater ground motion, and so on in a logarithmic series. Commonly, earthquakes are recorded with magnitudes from 0 to 8, although occasionally large ones (M=9) and very small ones (M= -1 or -2) are also recorded. Nearby earthquakes with magnitudes as small as 2 to 3 are frequently felt. The actual ground motion for, say, a magnitude 5 earthquake is about 0.04 millimeters at a distance of 100 kilometers from the epicenter; it is 1.1 millimeters at a distance of 10 kilometers from the epicenter. (2) A numerical expression of the amount of energy released by an earthquake, determined by measuring earthquake waves on standardized recording instruments (seismographs). The number scale for magnitudes is logarithmic rather than arithmetic; therefore, deflections on a seismograph for a magnitude 5 earthquake, for example, are 10 times greater than those for a magnitude 4 earthquake, 100 times greater than for a magnitude 3 earthquake, and so on