The first calculation of an earthquake 's seismic moment from its seismic waves was by Keiiti Aki for the 1964 Niigata earthquake . He did this two ways . First , he used data from distant stations of the WWSSN to analyze long-period ( 200 second ) seismic waves ( wavelength of about 1,000 kilometers ) to determine the magnitude of the earthquake 's equivalent double couple . Second , he drew upon the work of Burridge and Knopoff on dislocation to determine the amount of slip , the energy released , and the stress drop ( essentially how much of the potential energy was released ) . In particular , he derived a now famous equation that relates an earthquake 's seismic moment to its physical parameters : with being the rigidity ( or resistance ) of moving a fault with a surface areas of over an average dislocation ( distance ) of . ( Modern formulations replace with the equivalent , known as the " geometric moment " or " potency " . . ) By this equation the '' moment '' determined from the double couple of the seismic waves can be related to the moment calculated from knowledge of the surface area of fault slippage and the amount of slip . In the case of the Niigata earthquake the dislocation estimated from the seismic moment reasonably approximated the observed dislocation
1964 Niigata earthquake
1964 Niigata earthquake
Moment magnitude scale