Diurnal periodicity of the flow of Alaska earthquakes

The Alaska earthquake catalog has been analyzed in detail to find and study the diurnal periodicity of earthquake events. For this purpose, a set of spatially and temporally homogeneous samples of earthquakes with the well-known magnitude of completeness (Mc) has been prepared. For each sample, the spectra have been considered, the average diurnal variations in the number of earthquakes have been calculated, and their amplitudes were determined. The average diurnal variations were compared. For representative earthquakes in Alaska, no significant diurnal variation has been found. In subrepresentative samples, either the diurnal variation is insignificant or the signal-to-noise ratio only slightly exceeds 1.3–1.9. The diurnal variation is significant (a signal-to-noise ratio of 2.0–4.5) only for the samples of weak earthquakes with magnitudes of no more than 1.4, which is 0.5 units less than the strong (i.e., guaranteed for the entire sample area) completeness threshold. The results are consistent with the hypothesis explaining the diurnal periodicity of earthquakes by noise-discrimination effects. However, a comparative analysis of the diurnal variation parameters estimated over a large number of spatially and temporally homogeneous samples of earthquakes in the Alaska, southern California, and Greece catalogs shows that all of these results cannot be explained by this model.