Another nearly equivalent magnitude scale, M, the moment magnitude, is based on the seismic moment, M0 = mu A u (Aki, 1966), where A is the area of the earthquake rupture surface, u is the average fault displacement, and mu is the shear modulus of the crustal volume containing the fault. Hanks and Kanamori (1979) took advantage of the nearly identical relations between M0 and both ML and Ms to define M=2/3log10 M0-10.7, where M0 is measured in dyne-centimeters.