Deep Earthquake Mystery Finally Uncovered After Almost a Century Since Discovery

A distinguished professor in the Department of Mechanical and Aerospace Engineering at the UC San Diego Jacobs School of Engineering has uncovered the mysteries of the deep earthquake.

In her paper entitled "Volume collapse instabilities in deep earthquakes: a shear source nucleated and driven by pressure" that appears in the Journal of the Mechanics and Physics of Solids, mechanical engineer Xanthippi Markensoff showed that the mysterious earthquake originated between 400 and 700 kilometers below the Earth's surface and have been recorded with magnitudes of up to 8.3 on the Richter scale.

Solving the Mystery of the Deep-Focus Earthquake

The term deep-focus earthquake itself says that it originates deep with the mantle where high pressures are present. It was first identified in 1929 but researchers had not been able to pinpoint the relationship between high pressures and shear (distortional) seismic waves produced by deep-focus earthquakes.

Markensoff completes the explanation of this mystery that occurs under ultra-high pressures using a string of research papers since 2019. Her solution gives insight into many other phenomena that have similar geophysical processes, such as planetary formation, Phys.org reported.

Huajian Gao, a professor in Singapore's Nanyang Technological University and the Editor of the journal where Markensoff's paper appears, said that this discovery shows how deep mathematical modeling that is rooted in mechanics and physics could help in solving the mysteries of nature.

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What Causes Deep-Focus Earthquakes?

High pressures that occur 400-700 kilometers below the Earth's surface can cause olivine rock to turn into a denser type of rock called spinel, a process similar to how coal transforms into a diamond that also happens in the mantle.

EurekAlert! reported that the transform from rock to denser spinel leads to the decrease in the volume of the rock as atoms move closer to each other because of high pressures. This is called the volume collapse that is linked to transformational faulting, which is considered to be the predominant cause of deep-focus earthquakes.

But until today, no model based on volume collapse predicted the shear seismic waves. Markensoff used fundamental mathematical physics and mechanics to find instabilities that happen at very high pressures. These instabilities were the shape of expanding region of the transforming rock and the instability of its growth.

Markensoff concluded that deep-focus earthquake propagation is due to the pressure that acts on the change in volume. When asked how she felt about her discovery, she said that it feels like onding with nature by discovering the beauty of how it works.

Discovery Applicable in Solving Other Mysteries of Nature

The deep-focus earthquake is just one of which the instabilities manifest themselves. Markensoff's solution also gives an insight as to how other geological phenomena under high pressures happen, like planetary impacts and formation.

Experimental facilities that study such phenomena are now able to study materials under high pressures that were once impossible to test before.

Markensoff's work provides an important demonstration and reminder that harnessing the fundamentals of mathematical physics alongside experimental research done in extreme environments could help in solving the mysteries of nature.