Scientists think they know the reason behind the mysterious series of earthquakes between Fiji and Australia, and turns out, that it might be due to a new layer of the Earth’s mantle that is lurking under east Asia. This huge slab of ancient Earth, just emerged under the small pacific island of Tonga, which is right where most of the planet’s deepest earthquakes occur, and is travelling at about the same rate as the tectonic plates at the surface.
“Basically, 90 percent of Earth’s deep seismicity (more than 500 km deep) occurs at the Tonga area where we’ve found our long, flat slab”, said geologist Jonny Wu of the University of Houston to The Guardian.
The Earth’s Mantle has a thickness of about 3000 km’s and moves like a really thick liquid under our feet, and when the mantle moves, so does the crust, causing shifts on the tectonic plates.
Sometimes, the plates are moved apart, opening a breach on the ocean floor, and flooding it with hot magma from the mantle, yet other times, plates are compressed against each other, which causes earthquakes, mountain ranges, volcanoes and trenches. And of course, there’s always a chance that the plates go through a process named subduction, where one of the plates, is pushed down by the other, into the liquid mantle below.
Thanks to a new imaging technology, which uses earthquake data to analyze the Earth’s inner structure, Wu’s team discovered what seems to be multiple tectonic plates that were subducted around 50 million years ago.
Strangely, the plates were found sitting on the transition zone, between the upper and lower part of the mantle, roughly around 400 and 660 km, which goes against the logic, that tells us that the plates should have gone to the core, but instead, they are acting as they would at the surface.
“Beyond their choice of neighborhood, these sunken plates don’t differ that much from traditional plates in behavior”, explained Alexandru Micu for ZME Science. “One underlying principle of plate tectonics is that of isostasy, which basically says that … you can, in broad lines, delineate an area as being ‘the crust’, since most plates will bob around this mean elevation, and there’s no free magma on top, and ‘the mantle’, which is underneath this crust”, He added.
This is good news, has this provides an explanation to phenom known as Vityaz Earthquakes, that occur precisely in this area, and although more research is needed, this is a great first step in understanding the reason behind the deep Earth earthquakes.