Chris,

Tides depend on the moon, sun, and the response of the oceans. The effect of the sun and moon are simple to calculate, they are basically point masses at their great distances. The ocean response is equally important, but much harder to calculate, depending on the ocean bathymetry, and completely ignored by EQF.

As you probably know, the earthquakes are likely to respond to stresses aligned with the regional tectonic stress, not the just "big" tides, another detail ignored by EGF. Often, many components of the tides are in phase, but still one should know when big tides are encouraging, as opposed to discouraging, earthquakes with the typical focal mechanism for a region, another shortcoming of EQF's work.

Also, since the tides oscillate twice a day, the stress is only encouraging particular earthquakes for a few hours at a time, so people like Jim Berkland who predict for longer time windows are hoping, against all evidence to date, that bigger oscillations trigger more quakes than smaller oscillations, not that quakes are happening when the stresses are encouraging the quakes.

The most detailed studies (Tanaka's, mine, Tolstoy's, Knopoff's old work) occasionally show correlations, but none strong enough to provide useful warning information.

John