A new analysis denies the popular beliefs that large earthquakes tend to happen during certain phases of the moon or at certain times during the year.
The study, published in Seismological Research Letters on Tuesday, confirms that this bit of earthquake lore is incorrect.
After matching dates and lunar phases to 204 earthquakes of magnitude 8 or larger, dating back to the 1600s, Susan Hough of the United States Geological Survey has concluded that there is no evidence that the rates of these great earthquakes are affected by the position of the Earth relative to either the moon or the Sun.
The patterns that some observers see as linking large earthquakes with specific parts of the lunar cycle "are no different from the kinds of patterns you would get if the data are completely random," Hough noted.
To avoid detecting clusters of earthquakes within the data that are related to other factors, she chose to pare down the list to larger earthquakes because they are less likely to be an aftershock of a bigger earthquake.
Hough did see some unusual "signals" in the data. For instance, the highest number of earthquakes occurring on a single day, which is 16 times, came seven days after the new moon. But this signal was not statistically significant, "and the lunar tides would be at a minimum at this point, so it doesn't make any physical sense," she noted.
Hough said that the moon and Sun do cause solid Earth tidal stresses and could be one of the stresses that contribute in a small way to earthquake nucleation.
Some researchers have shown that "there is in some cases a weak effect, where there are more earthquakes when tidal stresses are high," she 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."
"Sooner or later there is going to be another big earthquake on a full moon, and the lore will pop back up," said Hough. "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."
