Key points are not available for this paper at this time.
The usual bias in earthquake catalogs against shocks of small magnitudes can be removed by testing the randomness of the magnitudes of successive shocks. The southern California catalog, 1933-1967, is found to be unbiased in the sense of the test at magnitude 4 or above; the cutoff is improved to M = 3 for the subcatalog 1953-1967.
Knopoff et al. (Fri,) studied this question.
Synapse has enriched one closely related paper. Consider it for comparative context: