Tidal triggering of earthquakes

In connection with earthquakes, syzygy refers to the idea that the combined tidal effects of the sun and moon – either directly as earth tides in the crust itself, or indirectly by hydrostatic loading due to ocean tides[2] – should be able to trigger earthquakes in rock that is already stressed to the point of fracturing, and therefore a higher proportion of earthquakes should occur at times of maximal tidal stress, such as at the new and full moons.

Previously, scientists have searched for such a correlation for over a century, but with the exception of volcanic areas (including mid-ocean spreading ridges)[3] the results have been mixed.

[4] It has been suggested that some negative results are due to failure to account for tidal phase and fault orientation (dip),[5] while "many studies reporting positive correlations suffer from a lack of statistical rigor.

[8] Research work has shown a robust correlation between small tidally induced forces and non-volcanic tremor activity.

[9] Volcanologists use the regular, predictable Earth tide movements to calibrate and test sensitive volcano deformation monitoring instruments.