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Seismic magnitude scales are used to describe the overall strength or "size" of an earthquake. These are distinguished from seismic intensity scales that categorize the intensity or severity of ground shaking (quaking) caused by an earthquake at a given location.
The moment magnitude scale ( MMS; denoted explicitly with M or Mw or Mwg, and generally implied with use of a single M for magnitude [1]) 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.
For large earthquakes worldwide, the moment magnitude scale (MMS) is most common, although M s is also reported frequently. The seismic moment, M 0 , is proportional to the area of the rupture times the average slip that took place in the earthquake, thus it measures the physical size of the event.
Seismic magnitude scales are used to describe the overall strength or "size" of an earthquake. 1 Earthquake magnitude and ground-shaking intensity. 2 Magnitude scales. 2.1 "Richter" magnitude scale. 2.2 Other "Local" magnitude scales. 2.2.1 Japan Meteorological Agency magnitude scale. 2.3 Body-wave magnitude scales. 2.3.1 mB scale. 2.3.2 mb scale.
These include body wave magnitude ( Mb) and surface wave magnitude ( Ms). Each is valid for a particular frequency range and type of seismic signal. In its range of validity, each is equivalent to the Richter magnitude. Because of the limitations of all three magnitude scales (ML, Mb, and Ms), a new more uniformly applicable extension of the ...
Methodology. The moment magnitude scale was designed to produce a more accurate accounting of the total energy released by an earthquake, and it calculates the earthquake’s magnitude more accurately than other measures—such as the Richter scale ( ML ), the body-wave scale ( mb ), and the surface-wave scale ( MS ).
Moment Magnitude (M W) is based on physical properties of the earthquake derived from an analysis of all the waveforms recorded from the shaking. First the seismic moment is computed, and then it is converted to a magnitude designed to be roughly equal to the Richter Scale in the magnitude range where they overlap. Moment (M O) = rigidity x ...
