Geologists have long been questioned about the possible influence of the moon and tidal motions on earthquakes, and recent studies provide a clearer picture of the situation.
According to a Japanese study, the great earthquakes seem to originate more likely during the stages of full moon or new moon; The two moon phases during which the tide motions are stronger.
Tokyo University researchers have analyzed three separate seismic databases: global data, and related to California and Japan, and focused on larger earthquakes (magnitude 5.5 or more) over the past 20 years.
Observing tidal weather data for the 15 days prior to earthquakes, the study determined that the largest earthquakes hit most of the time during the full or new moon phases.
In these moments of the lunar cycle, Sun, Moon and Earth are aligned, and the gravitational force of the Moon on Earth is at the height of its intensity.
Looking at the details in detail, 9 of the 12 strongest earthquakes (magnitude 8.2 or greater) over the last 20 years coincide with moments of strong lunar stress, such as that in 2004 in Sumatra (Indonesia) (magnitude 9.3); In Maule (Chile) in 2010 (magnitude 8.8); In Tohoku-oki (Japan) in 2011 (magnitude 9.0).
Are the moon phases causing earthquakes?
The Japanese study does not reveal a clear correlation between small earthquakes and lunar attraction; There is only a correlation with regard to larger earthquakes.
Correlation for minor shocks is reported by an US study on San Andreas's fault; Very small shakes (magnitude 1.0) seemed to be influenced by the Moon's position.
This second study is however smaller and limited in terms of samples.
Although the origin of earthquakes has not yet been fully understood by 100%, geologists believe that this is a cascading phenomenon, in which a small fracture becomes a major underground breach.
The data at our disposal seems to suggest that lunar gravitational attraction has a weak ability to produce earthquakes, but it is also efficient in transforming small shocks into disasters of great magnitude.
"A small fracture in the rock is more likely to become a huge breach during moments of intense gravitation lunar stress," Japanese researchers reported on the article in "Nature Geoscience."
"By studying the friction and friction of the rocks in the lab, we realized that the motion of the faults is not immediate. It may take hours, days, or even more time before stress triggers the movement that causes the earthquake, "says geologist Rebecca Boyle (not involved in research).
Conclusions? From the collected data, it is clear that the moon may play a role in triggering some earthquakes, but this is a very small contribution. Studies only establish a correlation and not a causality.
And the main causes remain the processes that take place deep inside the earth's crust, where tectonic plaques rub against each other, accumulating tensions that, even after hundreds of years, freed themselves suddenly, giving rise to seismic waves.
"The moon can only provide a small contribution of 1% to the tension of the tectonic plates," said geologist Nicholas van Der Elst at the Los Angeles Times.
"But that tiny contribution can be the drop that overflows the pot, to understand."
