What is moment magnitude?
Moment is a physical quantity proportional to the slip on the fault times the area of the fault surface that slips; it is related to the total energy released in the EQ. The moment can be estimated from seismograms (and also from geodetic measurements). The moment is then converted into a number similar to other earthquake magnitudes by a standard formula. The result is called the moment magnitude. The moment magnitude provides an estimate of earthquake size that is valid over the complete range of magnitudes, a characteristic that was lacking in other magnitude scales.
Moment magnitude is a specific way of measuring an earthquake based on how much of the fault slipped and how much it slipped. This is the magnitude of choice for seismologists and is the most accurate for the largest earthquakes. However, it is also one of the most difficult to compute. See Magnitude Scales in Section II – The Details for more information.
