The rate of decay of aftershocks of earthquakes in several tectonic settings will be analyzed by determining the parameters in the Modified Omori relation that fit the data best in the maximum liklihood sense. The important parameter is p, the exponent of time, t, in the aftershock decay relation, as defined by Omori (1894) and Utsu (1960). The parameters are determined by fitting the cumulative number of events up to any selected time, using the approach developed by Ogata (1983). Analyses of a number of well-documented aftershock sequences, described in the text of the proposal, yielded p-values from 0.7 to 1.3. From the few cases already studied for which the moment release pattern during the mainshock has been determined, a connection between the degree of uniformity of slip over the fault surface and the consequent decay rate of the aftershocks is suggested.
