Fluids play a vital role in deep-focus earthquakes, which occur between 300 and 700 kilometers beneath the planet's surface, according to a new study published in AGU Advances. Steven Shirey, Lara Wagner, Peter van Keken, and Michael Walter of Carnegie Mellon University and Graham Pearson of the University of Alberta make up the research team.

Common Earthquakes

The majority of earthquakes happen within 70 kilometers of the Earth's surface. They occur when tension builds up at fault between two chunks of rock, forcing them to slide past each other unexpectedly.

Deep Earthquakes

However, deeper within the Earth, the tremendous pressures generate too much friction for this type of sliding to occur, and the high temperatures help rocks bend to adapt to shifting stresses. Since the 1920s, scientists have been able to identify earthquakes that originate more than 300 kilometers under the surface, despite the fact that it is logically unthinkable.

Water has a role in intermediate-depth earthquakes, which occur between 70 and 300 kilometers under the Earth's surface, according to ongoing research over the past several decades. Water is released from minerals in these situations, weakening the rock near the fracture and allowing the chunks of rock to slip. However, scientists did not believe that this phenomenon could explain deep-focus earthquakes, mostly because water and other fluid-creating components could not go far enough into the Earth's interior to have a similar impact.

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Deep-Earth Diamonds

When Shirey and Wagner compared the depths of rare deep-Earth diamonds to the mystery deep-focus earthquakes, their perspective altered for the first time.

The diamonds not only signaled the existence of fluids, but they also transported deep-earth samples to the surface for scientists to investigate. When diamonds grow deep under the Earth's core, they can pick up mineral fragments from the surrounding rock. These minerals are known as inclusions, and while they may reduce the cost of your necklace, they are extremely useful to Earth scientists. They're one of the few means for scientists to examine firsthand samples of our planet's deep innards.

The inclusions in the diamond showed a chemical signature comparable to elements found in the marine crust. This indicates that water and other things did not form deep into the Earth's interior. They were instead swept down by a sinking oceanic plate.

Simulation

Wagner and van Keken put their theory to the test by using complex computational models to simulate the temperatures of sinking slabs at considerably larger depths than had previously been done. In addition to the modeling, Walter looked into the stability of the water-bearing minerals to see whether they could hold on to water in particular situations under the extreme heat and pressures of the Earth's deep interior. Even though warmer plates couldn't contain water, the study demonstrated that the minerals in colder oceanic plates might hypothetically transport water to the depths associated with deep-focus earthquakes.

The scientists compared the simulations to real-life seismological data to back up their findings. They demonstrated that the slabs that might theoretically transport water to these depths were also undergoing hitherto unexplained deep earthquakes.

This study is unique in that it examines the same subject using four separate disciplines: geochemistry, seismology, geodynamics, and petrology, all of which point to the same conclusion: water and other fluids are a fundamental component in deep-focus earthquakes.

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