Although we’re learning plenty by the day, there’s still a lot we don’t know about Antarctica. Lest we forget, it’s an enormous continental landmass covered and surrounded by ice that’s responding unevenly to the warming world. We’ve also, by the way, just this year had a detailed peek beneath the ice around the South Pole.
Fortunately, thanks to a suite of instrumentation implanted into the East Antarctic, we now know that East Antarctica isn’t bizarrely aseismic – as the data had suggested – but instead full of quakes and shakes.
A study dating back to 1986 explains that the first earthquake in the interior of the Antarctic continent was detected in Dronning Maud Land, which took place in 1982. In the years proceeding, several more were detected in various locations, and some were large enough to be located by the US National Earthquake Information Service.
It seemed odd, though, that so few quakes were being registered there, but no one could be quite sure why. As a new Nature Geosciences study elucidates, this is largely down to the fact that the underlying geology is somewhat ambiguous.
“Buried deep beneath the Antarctic polar ice sheet, the geological structure and tectonic activity of East Antarctica have long remained unknown,” the authors, led by Drexel University, explain.
Saying that, they note that the “apparent lack of tectonic seismicity” was anomalous relative to the interiors of other continents, which are rife with fault lines, mountain ranges, basins, and more, all undergoing tectonic stresses and strains. Why isn’t there more seismicity then?
This curious lack of shakes has been attributed to plenty of things in the past, including – but not limited to – the incredibly slow propagation of the tectonic plates here, or the massive overburden of ice preventing much movement. Still, it seemed odd to many. Was there something weird going on here?
Attempting to solve this mystery, the team – which also included Washington University and Pennsylvania State University – took to the icy realm to find out more.
They started to set up the world’s first winter-through-summer seismic array in the region in 2007 – no small feat in the harsh environmental conditions down there – and in 2009 alone, they detected 27 intraplate tectonic quakes. That alone tripled the total number of quakes registered in East Antarctica, which strongly suggests we just didn’t have enough instrumentation down there to pick up on the quakes in the first place.
These tremors, all registering as 2.1-3.9M events, mostly appear to be extensional, which means they are caused by tectonic stretching. The team noted that they are aligned with the Gamburtsev Subglacial Mountains, which could be part of an ancient continental rift system.
Evidence of continental rifting can be seen all over the planet. The East African Rift system is a fantastic example of how continental landmasses, allowing for the rise of a superheated mantle plume, are tearing themselves apart. Triggering earthquakes and some curious volcanism, if it continues, a brand-new ocean will form.
In this case, it appears that this far older, inactive continental rift system in Antarctica provided the area with a weak spot. This allows slips and sudden movements here to occur relatively easily, which creates the quakes picked up by the new array.
"I like to say that nature takes the path of least resistance," lead author, assistant professor Amanda Lough of Drexel University, told IFLScience. "There's also a possibility that we're seeing gravitational induced events due to the high topography on either side of the rifts."
Either way, this data demonstrates that East Antarctica is no more or less seismic than other massive, ancient continental landmasses around the world.
Another cold case solved, then!