Oceans Worth of Water Could be Trapped Beneath the Earth's Mantle

Large amounts of ocean water could be transported through deep-sea fault zones in volumes much greater than previously believed, according to new research from the University of Liverpool, which focused on the subduction zone that led to the 2011 Tohoku earthquake in Japan.

The research supports the theory that there could be vast amounts of water buried deep beneath the Earth's mantle.

Understanding how much ocean water is delivered to the mantle is important because it helps explain how the mantle bows and arches and how it melts, which helps solidify theories on the origins of plate tectonics and how the continental crust was formed.

Water is carried to the mantle via deep sea fault zones which breech the oceanic plate as it bends into the subduction zone, which is where one tectonic plate meets another and is forced beneath it. The largest earthquakes occur along subduction zones, such as the March 11, 2011 Tohoku earthquake, which registered at 9.0 on the Richter scale and triggered a devastating tsunami.

Based on their research, University of Liverpool seismologists suggest that over the age of the Earth, the Japan subduction zone alone could transport as much as three and a half times the water contained in all of Earth's oceans to the mantle. Some of this water gets cycled back out of the mantle, but some gets trapped deep within it.

"It has been known for a long time that subducting plates carry oceanic water to the mantle," said Tom Garth, a PhD student in the Earthquake Seismology research group at Liverpool.

"We found that fault zones that form in the deep oceanic trench offshore Northern Japan persist to depths of up to 150 kilometers," Garth said.

"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."

Garth and his colleagues' research is published in the journal Geology.