Psst. The moon takes about four weeks to go from full moon to full moon, so "within a week of full moon" is roughly 50% of all days - earthquakes or otherwise.
It is a joke - but intuitively you'd expect some correlation between tides and earthquakes. It would be somewhat surprising if such correlation did not exist, and then I'd wonder what does that mean for the mechanisms that produce EQs.
But the actual phase has nothing to do with it, the moons position around the earth does. It's possible to have a full moon over head or a new moon over head, the gravitational pull will be the same regardless of the phase. It's purely coincidental about it being a full moon.
The phase is important because tidal forces are the sum of forces from both the Sun and the Moon. When the Moon is full, that is because the Moon is directly opposite the Sun. When the Moon is new, that is because it is directly in front of the Sun.
This causes minimums and maximums in the tidal forces on the Earth.
> The phase is important because tidal forces are the sum of forces from both the Sun and the Moon. When the Moon is full, that is because the Moon is directly opposite the Sun. When the Moon is new, that is because it is directly in front of the Sun.
This causes minimums and maximums in the tidal forces on the Earth.
More pedantically, both those phases cause a spring tide (max tidal range). A neap tide (min tidal range) is when the sun and the moon are at right angles to the earth.
