Rock transformationAnother possibility is that the main type of rock found at this depth, called olivine, goes through a mineral transformation because of the enormous pressures it is under, which then triggers sliding between different types of rock.
A second paper in the same issue of Science bolsters the case for mineral transformation as the culprit for massive deep earthquakes.
In that study, researchers subjected a tiny chunk of olivine, just a few hundredths of an inch wide, to pressure 50,000 times atmospheric levels — equivalent to the pressure felt deep inside the mantle.
The olivine transformed to a different crystal structure called spinel, and shear waves (one of the two main types of waves generated by earthquakes) began propagating incredibly fast.
"These were propagating fast enough that they could radiate ultrasonic waves that we recorded," said study co-author Alexandre Schubnel, a materials scientist at the Centre National de la Recherche Scientifique in France.
The waves also had similar properties to those found in deep earthquakes, Schubnel said.
For instance, the transformation of olivine into its high-pressure crystalline structure is irreversible, so the rock couldn't experience aftershocks. In deep earthquakes, aftershocks are also uncommon, Schubnel said.
Even though the sample was tiny and the nano-earthquakes induced were a million, billion times less powerfujust a small fraction of the size of the biggest earthquakes, the physics behind the phenomenon is still the same, Schubnel said.
Both researchers said they were aware of the other's work, but that more research will be needed to pinpoint the cause of the Russian quake.
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