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