National News

Are Earthquakes More Likely During Full Moons? That’s a Myth, Study Finds

Posted January 18, 2018 2:17 p.m. EST

On Dec. 26, 2004, a magnitude 9.1 earthquake ruptured the ocean floor off the west coast of Sumatra. The resulting tsunami killed nearly 230,000 people in 14 countries, making it one of the deadliest natural disasters in history. And it occurred during a full moon.

The Sumatra earthquake isn’t the only large earthquake to have occurred beneath the moon’s bright glare. Both the earthquake that devastated Chile in 2010 and the Great Alaskan Earthquake in 1964 also happened on a conspicuous lunar date — making it tempting to argue that more large earthquakes occur during the full moon.

But a new study published in Seismological Research Letters finds that the connection is nothing but folklore.

To analyze the supposed link, Susan Hough, a seismologist at the U.S. Geological Survey, scrutinized 204 earthquakes of magnitude 8 or greater over the past four centuries. She then matched those earthquakes to the lunar calendar and found that no more occurred during a full or new moon than on any other day of the lunar cycle.

“The lore that the big earthquakes happen during the full moon — there’s no support for that in the catalog,” Hough said.

There is some sound science connecting Earth’s temblors and the moon. That’s because during full and new moons, Earth, the sun and the moon fall along a nearly straight line. This celestial alignment tugs at our planet, raising tides in the oceans and in the solid earth.

That effect is far too weak to cause an earthquake on its own. But should the moon’s gravitational pull tug at a fault that is dangerously close to rupture, a temblor is not impossible.

“It’s not some wild crazy idea,” Hough said.

But the gravitational effect is vanishingly small and only occurs under narrow circumstances, so it would never translate into a pronounced force — certainly not one that can be seen in a calendar or used to make predictions.

In 2004, for example, Elizabeth Cochran, a geophysicist with the USGS who was not involved in this study, and her colleagues published a study that did show a slight increase in the number of earthquakes during low tides — but only those in deep ocean basins.

Two years ago, a study by Satoshi Ide, a seismologist at the University of Tokyo, and his colleagues made headlines when it suggested that the number of high-magnitude earthquakes (like the one that occurred in Sumatra) also increases slightly as tidal stresses rise.

But again, this effect is so small that the probability an earthquake will occur during any given full moon remains no different than on any other day of the lunar cycle.

Such a minute change doesn’t help scientists predict when large earthquakes might occur, nor does it help regular citizens and emergency responders. There is simply too little power in the lunar tides.

In short, Hough’s study “debunks the prevalent superstition some people have that the moon tells us something about the danger,” said John Vidale, a seismologist at the University of Southern California who directs the Southern California Earthquake Center and was not involved in the new study.

Unfortunately, Hough doesn’t think the superstition will disappear anytime soon. But she hopes that studies like this can slowly chip away at the misconceptions, helping the public eventually realize that, no, the next full moon will not spawn a series of apocalyptic earthquakes.