When the sun, moon and Earth are aligned, high tidal stress may increase the chances that an earthquake will grow bigger than it otherwise might have been.
Every two weeks, on the full and new moons, the sun, moon and Earth fall along a nearly straight line. The combination of gravitational forces in this arrangement creates large swings in the tides. But the celestial alignment affects more than the oceans—it also tugs on Earth’s crust, adding to the stress on faults. This makes it more likely that major earthquakes will strike at these times, according to a new study.
The idea isn’t new, but scientists have had a hard time testing the earthquake-tide relationship. For instance, three of the largest earthquakes in recent years happened when tidal stress was high. But those big ones are rare and the link seems to break down for smaller events.
So the researchers crunched a bunch of numbers: by looking at more than 10,000 medium and large earthquakes, they found that the proportion of large events increased when tidal stress was high.
The study was published in the journal Nature Geoscience. [Satoshi Ide, Suguru Yabe and Yoshiyuki Tanaka, Earthquake potential revealed by tidal influence on earthquake size–frequency statistics]