In a report published Tuesday in the journal Seismological Research Letters, Susan Hough of the U.S. Geological Survey presents findings that a lunar-quake connection does not exist.
Furthermore, the patterns that have been cited previously as evidence of such a link “are no different from the kinds of patterns you would get if the data are completely random,” according to Hough.
Using the global earthquake catalog, Hough investigated the theory by looking at both the date and lunar phase of 204 earthquakes of magnitude 8 or larger since the 1600s. To avoid analyzing misleading data – like aftershocks of bigger earthquakes – she focused on giant quakes.
Hough’s analysis did find some clusters of earthquakes on certain days, the significance of which she tested by randomizing the dates of the quakes to determine what kind of patterns would materialize in these random data.
There were no differences between the kinds of patterns in the random data and the recorded earthquakes, according to the report.
“When you have random data, you can get all sorts of apparent signals, just like when you flip a coin, you sometimes end up with five heads in a row,” she said.
The report did note some unusual “signals” in the earthquake record, such as the greatest number of quakes – 16 – occurring a week after the new moon. However, this signal was not statistically significant, “and the lunar tides would be at a maximum at this point, so it doesn’t make any physical sense,” Hough noted.
Hough added that the sun and the moon do cause solid tidal stresses on Earth – ripples through the planet itself rather than waters hitting coastlines – which could be one of the factors that contribute somewhat to earthquake nucleation.
Some researchers have demonstrated that “there is in some cases a weak effect, where there are more earthquakes when tidal stresses are high,” Hough said. “But if you read those papers, you’ll see that the authors are very careful. They never claim that the data can be used for prediction, because the modulation is always very small.”
The theory that the positioning of the sun and the moon can affect earthquake rates on Earth has a long history, Hough noted.
“I’ve read Charles Richter’s files, the amateur predictors who wrote to him in droves, because he was the one person that people knew to write to … and if you read the letters, they’re similar to what people are saying now, it’s all the same ideas,” she said.
Hough doesn’t expect her findings to completely silence such theories.
“Sooner or later there is going to be another big earthquake on a full moon, and the lore will pop back up,” Hough said.
“The hope is that this will give people a solid study to point to, to show that over time, there isn’t a track record of big earthquakes happening on a full moon.”