Seismic moment is a quantity used by earthquake seismologists to measure the amount of energy released by an earthquake. The seismic moment M₀ is defined by the equation M₀ = μAu, where

• μ is the shear modulus of the rocks involved in the earthquake, typically 30 gigapascals[1]
• A is the area of the rupture along the geologic fault where the earthquake occurred, and
• u is the average displacement along the fault

The seismic moment of an earthquake may be estimated using whatever information is available. For modern earthquakes, moment is usually estimated from recordings of earthquakes known as seismograms. For earthquakes that occurred in times before modern instruments were available, moment may be estimated from geologic estimates of the size of the fault rupture and the displacement.

Seismic moment is the basis of the moment magnitude scale introduced by Hiroo Kanamori, which is often used to compare the size of different earthquakes.

See also: Richter magnitude scale

References

• Aki, K. and Richards, P. G. (2002). Quantitative seismology (2nd ed.). University Science Books. ISBN 0935702962.

• Fowler, C. M. R. (1990). The solid earth. Cambridge, U.K.: Cambridge University Press. ISBN 0-521-38590-3.