In anticipation of last night’s lunar eclipse several sites were trotting out the folklore that there are more earthquakes around the time of an eclipse. It seems like an easy thing to study–graph earthquake frequency over time, see if there are more during eclipses. Eclipses occur every couple of years, more often if you consider partial eclipses and small/medium earthquakes occur daily, so someone must have doen this. Looking around the web, the Goddard Space Flight Center answered a Science Question on this very topic (here):
Earthlings can view two lunar eclipses and two solar eclipses just about every year
It’s known that the tides during a lunar eclipse aren’t significantly different than tides during a full Moon. Each is just another spring tide — the name for tides that occur when the Earth is between the Moon and the Sun. If tides don’t really differ substantially during an eclipse than during regular full Moon or new Moon phases, why should celestial positions effect the Earth’s surface or subsurface features? The answer is that they don’t.
Earthquakes and volcanic eruptions do indeed occur at times of eclipses. But records show that they occur with no greater frequency or power than on days when full Moons or new Moons occur (without eclipses), when all the planets line up on the same side of the Sun or on days when the Moon is in a crescent or gibbous phase. As special as eclipses are, they simply don’t have a known impact on any geophysical phenomena.
And just how common are earthquakes anyway?
The ASK-AN-EARTH-SCIENTIST page by the U of Hawaii Geology and Geophysics Department says:
the Earth has about ten earthquakes of greater than magnitude 5 every day