Moment Magnitude

moment magnitude (M_W), also called moment magnitude scale, quantitative measure of an earthquake’s magnitude (or relative size), developed in the 1970s by Japanese seismologist Hiroo Kanamori and American seismologist Thomas C. Hanks. Calculations of an earthquake’s size using the moment magnitude scale are tied to an earthquake’s seismic moment (M₀) rather than to the amplitudes of seismic waves recorded by seismographs. The moment magnitude scale is the only scale capable of reliably measuring the magnitudes of the largest, most destructive earthquakes (that is, greater than magnitude 8).