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Ide et al. (2016) suggest that earthquakes (especially those of high magnitudes) are more probable during periods of high tidal stress (during full and new moons). While they show a comprehensive dataset and analysis to corroborate their claims, it contradicts previous findings (e.g., Kennedy et al., 2004). Their argument claiming that tides trigger the transformation from small fracture to the large rupture associated with large earthquakes seems counter-intuitive to me. Wouldn't it make more sense for the relatively small changes associated with the tidal stress to be more related to smaller earthquakes?

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I don't find Ide et al's recent paper to be very convincing. They only studied three earthquakes - hardly a statistically representative sample. There are millions of earthquakes on record, and hundreds of really big ones, of more than about MM 7.0, so there is plenty of scope for a more rigorous study. They occur at all phases of the tides. Some have claimed a weak correlation between tidal maxima and earthquake occurrence, but these are only just detectable above randomness, so maybe tides have an influence, albeit very small. The additional shear stress caused by tides is 2 to 3 orders of magnitude less than the stress release of an earthquake, so clearly other factors are much more important, such as the extent and location of fluid lubrication, and heterogeneity of friction along the slip plane.

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