There could be giant oceans beneath the Earth's surface.
New research suggests that deep-sea fault zones could actually pull water from the surface oceans into the upper mantle, a University of Liverpool news release reported.
These fault zones are able to penetrate the oceanic plate as it "bends into the subduction zone," (where one oceanic tectonic plate is forced beneath another, possibly causing an earthquake).
The researchers believe the Japan subduction zone could transport "three and a half times the water of all the Earth's oceans to its mantle," the news release reported.
The team used seismic modeling techniques to look at underground earthquakes occurring in the oceanic plate. They noticed the earthquakes took place in fault zones that had low seismic velocities. Seismic waves tend to travel more slowly in fault zones because seawater reacts with rock to form serpentinite (a mineral that contains water). As the tectonic plate heats up the water causes the mantle material to melt, creating volcanoes above the subduction zone.
"It has been known for a long time that subducting plates carry oceanic water to the mantle," Tom Garth a PhD student in the Earthquake Seismology research group said in the news release. "This water causes melting in the mantle, which leads to arc releasing some of the water back into the atmosphere. Part of the subducted water however is carried deeper into the mantle and may be stored there."
The study could help researchers gain insight into the origin of plate tectonics and how the Earth's continental crust was formed.
"We found that fault zones that form in the deep oceanic trench offshore Northern Japan persist to depths of up to 150 [kilometers]. These hydrated fault zones can carry large amounts of water, suggesting that subduction zones carry much more water from the ocean down to the mantle than has previously been suggested," Garth said. "This supports the theory that there are large amounts of water stored deep in the Earth."
