Hiding beneath the earth's deepest core, this mineral's transformation into another form can trigger some of the deepest earthquakes ever detected.
The deep-focus earthquakes or cryptic tremors are a seismic conundrum. The tremors are ruptured and have a depth greater than 300 kilometers, with extreme humidity and pressure that will force the rock to flow smoothly.
Some experiments suggest the same hellish condition may also transform olivine, a primary mineral that is usually seen in the Earth's mantle, into the mineral wadsleyite. The experiment was included in the research that was published in the Nature Communications Journal, last Sept. 15.
The olivine mineral metamorphosis "can destabilize the surrounding rock," enabling earthquakes at otherwise impossible depths according to the main physicist Tomohiro Ohuchi and the other researchers of the study.
Unstable Olivine Mineral Possible Results
Ohuchi of Ehime University described the research as challenging and said, "It's been a real puzzle for many scientists because earthquakes shouldn't occur deeper than 300 kilometers." The cryptic tremors usually take place at subduction zones where the tectonic plates made of oceanic crust fall towards the mantle.
Since the seismic waves of earthquakes lose strength during their long ascent to the earth's surface, they aren't that dangerous. There are some instances when the shaking isn't that powerful. In 2013, a deep-focus earthquake, with a magnitude of 8.3, struck around 609 kilometers below the Sea of Okhotsk, east coast of Russia.
Previous research indicates that the unstable olivine mineral can lead to deep earthquakes. But Ohuchi says that those researchers tested other minerals that were the same in composition as olivine, but they deformed under low pressure. He added that the experiment didn't stress the sample enough to create defects.
Ohuchi's Team Experiment
To replicate the conditions beneath the earth's underground, Ohuchi and his team put the olivine crystal to the test. They heated and squeezed the olivine minerals at 1100 degrees Celsius and 17 gigapascals. They used a mechanical press to gently compress the crystal and monitored the physical changes.
They adjusted the experiment's main attributes. The 11 gigapascals were later changed to 17, and 800 Celsius was adjusted to 900. The olivine was recrystallized into thin layers that contained new wadsleyite and smaller grains.
They also found small faults and recorded sound wave bursts, which are indicative of minor earthquakes. They suggested that, with subducting tectonic plates, a great portion of these thin layers rise and create weak areas in the rock over where faults and earthquakes can start.
University of Nevada's geophysicist Pamela Burnley stated, "Change Really Wreaks Havoc" [rock's] mechanical stability." She claimed that the findings helped confirm that olivine metamorphosis was enabling deep-centered quakes.
Ohuchi's team is targeting process experiments on olivine at higher pressures to have insights into the changes of the mineral at deeper depths.
According to Aessoil, olivine mineral has been found in stony and stony-iron meteorites near Mars and Jupiter. But it is a distinct form that can be also seen on the planet or asteroid near the boundary of the mantle core.
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