Moment magnitude scale

The moment magnitude scale (a successor to the Richter scale), was introduced in 1979 by Tom Hanks and Hiroo Kanamori and is used by seismologists to compare the energy released by earthquakes. The moment magnitude M_mathrm{w} is a dimensionless figure defined by

Related Topics:
Richter scale - Tom Hanks - Hiroo Kanamori - Seismologist - Earthquake

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:M_mathrm{w} = {2 over 3}left(log_{10} rac{M_0}{mathrm{N}cdot mathrm{m}} - 9.1 ight) = {2 over 3}left(log_{10} rac{M_0}{mathrm{dyn}cdot mathrm{cm}} - 16.1 ight),

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where M_0 is the seismic moment.

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An increase of 1 step on this scale corresponds to a 101.5 = 31.6 times increase in the amount of energy released,

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and an increase of 2 steps corresponds to a 103 = 1000 times increase in energy.

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The constants in the equation are chosen so that estimates of moment magnitude roughly agree with estimates using other scales such as the Richter magnitude scale. One advantage of the moment magnitude scale is that, unlike other magnitude scales, it does not saturate at the upper end. That is, there is no particular value beyond which all large earthquakes have about the same magnitude. For this reason, moment magnitude is now the most often used estimate of large earthquake magnitudes. The USGS does not use this scale for earthquakes with a magnitude of less than 3.5.

Related Topics:
Richter magnitude scale - USGS - Earthquake

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