When it comes to earthquakes, Antarctica has always been the calm, frozen outlier. Most of the planet’s shaking occurs where tectonic plates grind against each other, and Antarctica is in the middle of one giant plate, far from those messy edges. That reputation just received a blow. In a new study published in the journal Science, researchers used artificial intelligence to comb through two decades of old seismic data, uncovering more than 500 previously unreported earthquakes lurking beneath the East Antarctic Ice Sheet. And they were not where anyone expected to find them.
The story turns things around for an American audience accustomed to hearing about earthquakes in California or Alaska. According to the same Science study, these quakes occurred about 60 to 90 miles down, beneath a massive river of ice called the David Glacier, which stretches nearly 700 miles and dumps about 4 percent of the entire East Antarctic Ice Sheet into the ocean.
Why this site puzzles geologists
What’s confusing for experts is that earthquakes this deep, called intermediate-depth earthquakes, almost always occur at subduction zones: the boundaries where one tectonic plate dives beneath another. According to the study's authors, David Glacier isn't close to a plate boundary. It sits in the middle of a single plate, which makes these quakes a real puzzle to the science of plate tectonics.
So what’s shaking the ground in a spot where it shouldn’t? According to lead researcher Long Ho, a geologist at the University of Alabama, the explanation comes down to the temperature differences deep in the Earth. The crust and upper mantle beneath East Antarctica are cold and stiff, whereas beneath West Antarctica they are warm and weak. Ho says the contrast between the two very different zones where they meet creates intense stress, which triggers the tremors. The detected quakes ranged in magnitude from 1.6 to 3.5, the same report said. Near David Glacier, the edges of the crust are being bent by warm material rising from the upper mantle beneath West Antarctica, building pressure that is eventually released as small earthquakes.
