Earthquake, Magnitude of an
Earthquake, Magnitude of an : A quantity characteristic of the total energy released by an earthquake, as contrasted to "intensity," which describes its effects at a particular place. Magnitude is determined by taking the common logarithm (base 10) of the largest ground motion recorded on a seismograph during the arrival of a seismic wave type and applying a standard correction factor for distance to the epicenter. Three common types of magnitude are Richter (or local) (ML), P body wave (mb), and surface wave (Ms). Additional magnitude scales, notably the moment magnitude (Mw), have been introduced to increase uniformity in representation of earthquake size. Moment magnitude is defined as the rigidity of the rock multiplied by the area of faulting multiplied by the amount of slip. A one-unit increase in magnitude (for example, from magnitude 6 to magnitude 7) represents a 30- fold increase in the amount of energy released. See: Intensity (of an earthquake)
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