Study: Earth Has Secret Underground Oceans
Earth could actually have much more water than anyone thought.
A new study by scientists at the University of Liverpool, England, suggests massive amounts of water, enough to fill entire oceans, may well be pouring down from the oceans to the planet's upper mantle through deep sea fault zones.
The findings were published in the journal Geology.
"It has been known for a long time that subducting plates carry oceanic water to the mantle," said Tom Garth, a doctoral student in the school's Earthquake Seismology research group. "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."
Garth added in the announcement that researchers "found that fault zones that form in the deep oceanic trench offshore Northern Japan persist to depths of up to 150 km. 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."
Judging by the age of the earth alone, Garth and his colleagues estimate the subduction zone off the coast of Japan could have carried down to the mantle as much as three-and-a-half times the water of all the surface oceans combined.
Using seismic modeling techniques, the scientists analyzed earthquakes that occurred more than 100 km below the Earth's surface in the Wadati-Benioff zone, a seismically-active region that often can stretch as far as 670 kilometers, or over 400 miles, below the area where one oceanic plate sinks under another plate and heads deep into the mantle.
Researchers discovered certain seismic waves in the region of study occurred along 1-2 km-wide faults zones and had relatively low velocities -- evidence that the waves were traveling through minerals formed by the combination of material in the planet's mantle and water.
"These hydrated fault zones can carry large amounts of water," some of which is carried to the mantle but also released when the involved tectonic plates heat up.
The collected water causes the mantle material to melt, leading to volcanoes above the subduction zone, like those that form the "Pacific Ring of Fire."
Meanwhile, much of the water that doesn't interact with the molten rock is conveyed even deeper into the mantle, where it has stayed.