Giant Diamonds Might Hold the Key to Superdeep Earthquakes

According to most geophysical models, earthquakes should not happen more than 300 kilometers beneath Earth’s surface. However, they commonly do, an event that has confounded seismologists for years.

Researchers suggest that water transported by tectonic plates shoved beneath continents might be setting off these deep temblors. The find may also clarify another wonder: why a substantial number of fist-size diamonds form at this depth.

Quakes typically occur when both sides of a fault, or the opposite sides of a tectonic plate boundary, scrape past each other. Far below our planet’s surface, the pressures are too high for such slippage, and rocks are typically so hot they ooze and flow instead of break. That has led geophysicists to find alternate explanations for deep seismic activity, which can be very strong but too distant for us to feel.

Underground seismic activity

One ideology is that some minerals, under the extreme heat and pressure deep within our planet, can immediately lose volume, with the runaway collapse over large distances creating solid quakes.

The second idea is that once a quake gets going– due to the sudden collapse of minerals or other reasons– rocks near the tip of the rupture warm up even further and weaken, sustaining the earthquake.

A third reason might be water launched from rocks deep below Earth’s surface, which could compromise other rocks nearby, permitting them to fracture more simply. However, scientists have incredibly disregarded that explanation because it was unclear where such water would be coming from.

Diamonds might be the answer

Steven Shirey, a geochemist at the Carnegie Institution for Science, had a hunch: diamonds. The valuable gems can accumulate layers as they grow, collecting imperfections– such as flecks of surrounding rocks– as they grow. Those supposed inclusions can likewise have pockets of the mineral-rich water.

To see whether the concept could work, Shirey and his team looked closely at how water might make its way down deep. The explanation, they believe, is that it flights down within tectonic slabs as they get shoved beneath continents.

There are three origins of water, they postulate. One was that the water was locked in the minerals that developed as molten rock solidified at midocean ridges. Another was the wet sediments that gathered on those slabs as they crossed the ocean floor. And the third was ocean water that penetrated the slabs as they curved and fractured.

Over the simulation

The scientists utilized computer simulations– and the outcomes of previous laboratory research by their group and others– to examine precisely how minerals in those slabs would act as they moved deeper and deeper.

Generally, as deepness within Earth enhances, so do temperature and pressure. Slabs can initiate relatively cold at Earth’s surface; they warm up as they sink. And because they are lots of kilometers thick, it frequently takes millions of years for the slabs to heat throughout.

Independently of deepness, Shirey and his group found that once rocks in the slabs reached temperatures over 580 ° C, they were less able to hold water.

As that water flooded out of the slab, it compromised the surrounding rocks and triggered earthquakes, Shirey and his colleagues reported in AGU Advances.

This water, typically chock-full of dissolved minerals, would also be offered to sustain diamond development.

The temperature tells the story

“The temperature tells the story,” says Douglas Wiens, a seismologist at Washington University in St. Louis who was not involved in the new research. If the tectonic slab starts hot, as it would if the rocks are relatively young, he claims, the plate will dehydrate at depths between 100 and 250 kilometers and therefore will not carry water far enough down to create a deep earthquake.

If rocks in the sinking slab are old and also reasonably cold, water will undoubtedly stay secured inside the sinking slab for a longer time, persisting there until it is released at a deepness of 300 to 500 kilometers or more.

More work in both the lab and the field will be necessary to comprehend the connections between water launched from sinking slabs and deep quakes, Wiens claims. In the meantime, he says, it is clear that diamonds that form at those deepness, imperfections and all, will be critical to tease out the information of the tale.

Read the original article on Science.

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