Uncommon
Moment magnitude scale
Measure of earthquake size
Moment magnitude scale
The moment magnitude scale (MMS; denoted explicitly with Mw or Mwg and generally implied with use of a single M for magnitude) is a measure of an earthquake's magnitude ("size" or strength) based on its seismic moment. Mw was defined in a 1979 paper by Thomas C. Hanks and Hiroo Kanamori. Before Hanks and Kanamori (1979) , Kanamori (1977) developed Mw scale for large earthquakes above 7.5. Thus Mw and M are not the same mathematically even though they are considered the same. Similar to the local magnitude/Richter scale (ML) defined by Charles Francis Richter in 1935, it uses a logarithmic scale; small earthquakes have approximately the same magnitudes on both scales. Despite the difference, news media often use the term "Richter scale" when referring to the moment magnitude scale. Moment magnitude (Mw) is considered the authoritative magnitude scale for ranking earthquakes by size. It is more directly related to the energy of an earthquake than other scales, and does not saturate – that...
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