The moon’s gravity is constantly pulling on the Earth.
The attraction to the oceans is undeniable, but some scientists have studied less visible effects.
They found that the moon could potentially trigger earthquakes, when the time is right.
Our moon undeniably influences the tides of the earth. Its gravitational pull causes rises and falls in our planet’s sea level.
But what if the moon had a smaller, less visible effect on our planet?
A small handful of experts claim to have evidence that our satellite produces forces that can cause earthquakes.
The moon’s effect on earthquakes was hidden
Scientists have long pondered whether the moon’s tides could be associated with earthquakes. After all, our satellite is always there, displacing the weight of the oceans and pulling on our planet.
Surely all that pressure, even if incremental, would add up to a significant effect, scientists asked.
But until recently, datasets weren’t good enough to show the link between the moon and earthquakes, and its gravitational pull was thought to be too weak to have any significant impact.
“For a while it was a field where only fools worked,” Chris Scholtz, a geologist and emeritus professor of earth and environmental sciences at Columbia Climate School, told Insider.
But with the advent of larger and more comprehensive data sets over the past 20 years, the moon’s influence is beginning to emerge from the data. And it seems that in some cases the moon has caused earthquakes around the world.
“With these huge datasets, they started to get a small but significant correlation,” Scholtz said, adding, “Now it’s believable,” he said.
The moon can put the weight of the ocean on a volcano
One place where the impact of the moon can be clearly seen is in underwater earthquakes. That makes sense, given the gravitational pull of the moon on the oceans.
For example, a 2004 paper published in the peer-reviewed journal Science found that earthquakes along underwater fault lines seemed to follow ocean tides.
Scholtz and his team set out to investigate how the moon might exert its force on the earthquakes on the axial volcano on the Juan de Fuca ridge off the west coast of the US. Earthquakes are about 10 times more likely here once the tide has gone out, Scholtz said.
Their study, published in Nature Communications in 2019, found an explanation for the link between the moon and earthquakes. It suggested they were caused by the weight of the ocean pressing on a volcano’s magma chamber.
“What happens is the tides cause the magma chamber to inflate and deflate,” he said. “That’s what causes the earthquakes.”
When the tide is low, less water presses on the chamber, which then inflates. This, in turn, puts more pressure on the fault line, making it more likely to shake and cause an earthquake.
The moon also pulls on the rocks of the earth
It’s not just in the oceans where the moon wreaks havoc. Although we may not feel it, the moon also causes small, but important, tides in rocks.
Standing on the surface of the earth, it can be hard to imagine mountains ebbing and flowing like the ocean, but rocks bulging and crushing under the gravitational pull of the moon
“The solid Earth tides are the same as the tides, it’s just on the solid Earth. And the amplitude of motion is very small because the Earth is very stiff,” Scholtz said.
“You can measure it with a very sensitive instrument, but you don’t notice it,” he said.
These tides can warp the Earth about 22 inches vertically and about 11 inches horizontally each day, Davide Zaccagnino, a geophysics doctoral student at the Sapienza University of Rome, told Insider in an email.
By digging into these datasets, a few studies have suggested a link between terrestrial tides and earthquakes.
“While fluids can flow, rocks can change shape only slightly depending on the intensity and direction of the tidal disturbance, promoting stress accumulation,” Zaccagnino said.
If rocks are already overstretched due to the action of tectonic forces, even a small strain from the moon’s gravitational pull could be the straw that breaks the camel’s back, causing a crack in the rock, he said.
“If surrounding rocks are also unstable, the rupture can accelerate and bring large fracture areas. The final result is an earthquake,” Zaccagnino said.
It can push earthquakes over the edge
Let’s get one thing straight: the moon doesn’t cause these earthquakes. Rather, it’s when the rock is on the verge of collapse that the moon’s little tug can push it past that final tipping point.
This only happens in very specific circumstances, such as when the pressure of the moon’s gravity is perfectly aligned with the fault line. So it’s not like we could say that every earthquake is more likely when the moon is shining.
“Tides can’t help us predict earthquakes, but they can help us better understand their physics, which are still largely unknown,” Zaccagnino said.
Knowing when the moon’s gravitational pull could have triggered an earthquake, for example, could help us understand when the crust was at a breaking point, Zaccagnino said.
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