Reliable estimation of the seismic moment of large earthquakes.

Large earthquakes on the Pacific coast are characterized, on the average, by σ≈30 bars and L≈2w independently of the size, where σ is the stress drop, L is the fault length, and w is the fault width. It follows from these that the seismic moment is determined straightforwardly from the fault size alone. Such a convenient method of estimation of the seismic moment is also applicable to the major earthquakes in the Japanese islands which are characterized, on the average, by σ≈60 bars and L≈2w. These results can be used for reliable assignment of moment to future large earthquakes as well as historical large earthquakes for which detailed mechanism studies cannot be made. The uncertainty in the method presented here is much less than that in estimating moments from the earthquake magnitude.