The magnitude distribution of declustered earthquakes in Southern California

The binned distribution densities of magnitudes in both the complete and th e declustered catalogs of earthquakes in the Southern California region hav e two significantly different branches with crossover:magnitude near M = 4. 8. In the case of declustered earthquakes, the b-values on the two branches differ significantly from each other by a factor of about two. The absence of self-similarity across a broad range of magnitudes in the distribution of declustered earthquakes is an argument against the application of an:ass umption of scale-independence to models of main-shock earthquake occurrence , and in turn to the use of such models to justify the assertion that earth quakes are unpredictable. The presumption of scale-independence for complet e local earthquake catalogs is attributable, not to a universal process of self-organization-leading to future large earthquakes, but to the universal ity of the process that produces aftershocks, which dominate complete catal ogs.