  We revisit the work of Kilston and Knopoff (1983) to study the correlation of
earthquakes with the main lunisolar tidal components in the limited zone of the
Southern California region, with a considerably bigger amount of data. By
adopting the same methodology as these authors, we confirm their results, i.e.
that strong earthquakes with M >= 6 show a statistically significant
correlation with half day and precession cycles, with respective periods 12 hr.
and 18.6 y., while weaker earthquakes show a correlation with the annual cycle.
Moreover we extended the study to the analysis of bi-modal phase to phase
diagrams, leading to a very high probability of a lack of earthquake
occurrences when both phases of the 12 hr. and 18.6 y. cycles are inside the [0
- 0.5] interval. Furthermore, we demonstrate that the statistical method is not
really appropriate to study the correlation with the semi-lunar day and the
fortnightly tidal components.
