Earthquakes happen all the time, but they are arguably the most enigmatic type of natural disaster – even their triggering mechanisms can be highly mysterious in some instances. A truly astonishing new study in Nature Geoscience has revealed that some of the most powerful quakes in human history could have been set off by nothing other than the Moon.
It’s well known that the Moon’s minor gravitational field, along with that of the Sun, pulls at Earth’s oceans, generating tides on very predictable time cycles. In other parts of our Solar System, the gravitational dance of various moons and planets can generate such powerful tidal forces that rock is pulled apart into molten lava.
Seismologists have often wondered if we have been underestimating the power of our very own pale companion. It certainly can’t melt rock down, but could it exert enough force to break weak rocks apart?
Certain deep-seated fault lines with subduction zones – areas where a denser tectonic plate slides beneath another – are understood to be particularly prone to sudden slippage. With this in mind, a team from the University of Tokyo hypothesized that the Moon’s influence may be triggering small ruptures that permit the entire fault section to mobilize.
In order to test this idea, they looked back through data sets over the last 20 years to see if major quakes have taken place along with syzygies, which denote new moons or full moons. At these points, the Sun and Moon are in alignment and the gravitational fields of both interact with each other.
When Earth experiences a full moon, the Sun is pulling at one hemisphere, and the Moon is tugging at the other. In theory, this type of stress could pull certain rocks apart.
Remarkably, during some of these full moon syzygies, several destructive tremors were initiated, including the devastating 2004 Sumatran event, which generated a tsunami that claimed nearly a quarter of a million lives. A powerful 8.8M quake in Chile in 2010 is another example, one of the most powerful ever recorded.
The tsunami-generating energy output of the 2010 Chilean quake. NOAA
Previous studies have looked at periods of peak tidal stress, which would be during a new moon. At this point, the Sun and Moon are on the same side of Earth, and their gravitational fields “team up” to pull even more strongly on that hemisphere of the world. This was also enough to apparently initiate the horrifying 2011 Tohoku quake, whose accompanying tsunami smothered much of Eastern Japan.
Although there is no direct evidence linking syzygies of both kinds to the physical rupturing of these major subduction zone faults, the correlation – which isn’t linked to any one particular region of the world – is the strongest on record. It may still be circumstantial evidence, but it’s a very compelling argument that suggests that big things have small beginnings.
“[Our study] suggests that the probability of a tiny rock failure expanding to a gigantic rupture increases with increasing tidal stress levels,” the authors note in their paper. “We conclude that large earthquakes are more probable during periods of high tidal stress.”
There has been an increasing amount of evidence in the last few decades that suggests the gravitational influence of the Moon and Sun could be conspiring to pull apart structurally weak faults that were due to release some stress. The San Andreas Fault, for example, has experienced more than 80,000 small tremors related to the lunar cycle.
If it’s triggering these quakes, then should we attempt to destroy the Moon? Ultimately, no – the Moon may also be stirring tides deep within Earth’s liquid core. Without these tides, we may not have a protective magnetic field shielding us from harmful radiation.
Every cloud has a silver lining.
Iwate prefecture damage in Japan as a result of the 2011 quake and tsunami. yankane/Shutterstock