(ORDO NEWS) — Scientists from the University of California have found out why, at a depth of 400-700 kilometers, the magnitude of the tremors on a rating scale was 8.3 points.
It was not clear how and why tremors appeared at such a depth. Common earthquakes cause lithospheric plate joints. What provokes the deep ones was a mystery, but now the mystery has been solved.
It is reported by Phys.org.
For the first time, such tremors were recorded almost 100 years ago. Then they got the name “deep focus earthquakes”. They take place deep in the mantle of the earth. Previously, it was believed that such emissions provoke too high pressure, and in such a way energy is simply thrown.
However, the theory had many flaws. The main one is the lack of relationship between high pressure points and seismic waves.
High pressure at depths of up to 700 kilometers is lower than at the surface of the earth. The pressure difference converts the olivine rocks to spinel.
Spinel is a harder, denser mineral and since it is compressed by pressure differences, voids form in the depths. These voids are like a flattened pancake spreading around the edges.
Previously, scientists believed that these voids were in the shape of a sphere, and therefore excluded the possibility of earthquakes.
The spherical shape simply could not cause shear seismic waves. Almost 100 years later, it was possible to find out this scientific error. Now knowing the truth, seismologists can know in front where such tremors will occur.
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