For decades, Antarctica has been considered one of the quietest seismically speaking continents on the planet. The neural network, trained to recognize weak fluctuations in the soil, forced us to reconsider this opinion.
There are earthquakes under Antarctica. Photo: Wikimedia
A hidden source of underground activity has been found under the ice of Antarctica, which has remained unnoticed for several decades, Futurism reports. A group of geologists studied archival seismic records under the David Glacier, a massive ice mass stretching over 1,120 km, and discovered hundreds of small tremors that no one had previously known about.
For the analysis, the researchers used two sets of data: records from 2001 to 2004 and from 2012 to 2015. The tremors themselves turned out to be weak — the magnitude ranged from 1.6 to 3.5, that is, a person on the surface would hardly have felt them. But something else turned out to be unusual: the foci lay at a depth of over 70 kilometers, well below the boundary between the earth’s crust and mantle.
It is this depth that has become a mystery. Such tremors belong to the category of intraplate earthquakes of intermediate depth — events that occur not at the junction of tectonic plates, but in their thickness. It is extremely difficult to explain such foci using the classical theory of plate motion. Usually, seismic activity is concentrated in subduction zones, where one plate runs over another. Here, the tremors were born in the very middle of the plate, far from the usual boundaries.
A version has been proposed related to the temperature difference inside the lithosphere, the solid outer shell of the planet. Under West Antarctica, this shell is relatively warm and soft, while under East Antarctica it is cold, dense and hard. At the boundary between these two zones, there is a sharp drop in the mechanical properties of rocks, and it is there, according to scientists, that bending stress accumulates. When it exceeds the tensile strength, a rupture occurs — in fact, an earthquake.
Richard Alley, a geologist at the University of Pennsylvania who was not involved in the study, noted an important thing about this: the absence of recorded tremors in the past meant not the absence of activity itself, but a lack of instruments and methods for detecting it. Modern machine learning algorithms have been able to “hear” signals that were previously drowned in noise or simply not recognized as earthquakes.
Scientists suggest that similar intraplate tremors at intermediate depths may exist in other regions of the planet, remaining unnoticed for the same reason — the lack of sensitive detection systems. They plan to apply similar neural network algorithms to the seismic archives of other continents.
Earlier this year, another group of researchers found similar foci in depth — the so-called continental mantle earthquakes at around 90 kilometers. However, the mechanism of their occurrence seems to be fundamentally different, which indicates a greater variety of deep geological processes than previously thought.
By Daria Artsybasheva
earthquakes
