Giant Diamonds May Hold the Key To Superdeep Earthquakes

'Earthquakes shouldn't occur more than 300 kilometers below Earth's surface, according to most geophysical models,' reports Science magazine. 'Yet they commonly do — a phenomenon that has mystified seismologists for decades.'

Slashdot reader sciencehabit shares their report on one possible explanation: that water carried by the tectonic plates shoved beneath continents 'could be triggering these deep temblors.'

The find may also explain another marvel: why a huge number of fist-size diamonds form at this depth...

Steven Shirey, a geochemist at the Carnegie Institution for Science...and his team took a closer look at how water might make its way down deep... Regardless of depth, Shirey and his team found that once rocks in the slabs reached temperatures above 580 degrees C, they were less able to hold water. As that water flooded out of the slab, it weakened the surrounding rocks and triggered quakes, Shirey and his colleagues report in AGU Advances. This water, typically chock-full of dissolved minerals, would also be available to fuel diamond formation...

'The temperature tells the story,' says Douglas Wiens, a seismologist at Washington University in St. Louis who was not involved in the new study. If the tectonic slab starts out hot, as it would if the rocks are relatively young, he says, the plate will dehydrate at depths between 100 and 250 kilometers and thus won't carry water far enough down to generate deep quakes. But if rocks in the sinking slab are old and relatively cool, water will stay locked inside the sinking slab for a longer time, persisting there until it is released at depths of 300 to 500 kilometers or more.

Further work in both the lab and the field will be needed to fully understand the relationships between water released from sinking slabs and deep earthquakes, Wiens says. In the meantime, he says, it's clear that diamonds that form at those depths, imperfections and all, will be critical to teasing out the details of the story.

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