Engineering Professor Solves Mystery of Deep Earthquakes

Deep-focus earthquakes were first discovered almost a hundred years ago.
Chris Young

An engineering professor from the UC San Diego Jacobs School of Engineering, Xanthippi Markenscoff, solved a mystery regarding deep earthquakes that has baffled the scientific community since they were first discovered in the 1920s. Her findings are presented in the Journal of the Mechanics and Physics of Solids.

Scientists in the 1920s discovered a mysterious phenomenon occurring far below the Earth's crust: earthquakes are occurring in regions where they should not be possible, according to the latest scientific understanding.

The mysterious earthquakes originate between 400 and 700 kilometers (250-430 miles) below the Earth's surface and have been recorded with magnitudes up to 8.3 on the Richter scale.

Going by the term "deep-focus earthquake," the mysterious deep earthquakes — which originate under incredibly high-pressure conditions within the Earth's mantle — were first discovered in 1929.

Scientists had previously posited that the high-pressure environment deep below the Earth's surface might cause an implosion, leading to deep earthquakes. However, they were not able to find sufficient evidence to back up the theory.

The origin of deep-focus earthquakes

In her new study, Markenscoff provides a new solution for the deep-focus earthquakes, alongside ample evidence provided via computer modeling.

Advanced technologies have increasingly played a role in understanding earthquakes in recent years — a Stanford AI detection system, for example, could be used to predict earthquakes in the future. The European Space Agency's GOCE satellite mission, meanwhile, has provided accurate gravity-based measurements of the Earth's upper mantle and crust.

Markenscoff's study is rooted in the fact that the high-pressure environment 400-700 kilometers (250-430 miles) below the Earth's surface is known to cause olivine rock to turn into a denser type of rock called spinel — a process that somewhat resembles the transformation of coal into diamond under when it's under immense pressure.

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The transformation from rock to spinel leads to a decrease in the volume of the rock due to the high-pressure environment. This so-called "volume collapse" is linked to transformational faulting, which is presented as the main cause of deep-focus earthquakes in Markenscoff's paper. 

Using mathematical models and simulations, Markensoff concluded that deep-focus earthquakes occur due to the effects of the high pressure in combination with the shift in volume during the "volume collapse."

Asked how she felt about her groundbreaking findings, Markenscoff said "I feel like I have bonded to nature. I have discovered the beauty of how nature works."

"It's the first time in my life. Before it was putting a little step on someone else's steps. I felt this immense joy," she explained in a UC San Diego press release.

The new study adds to a growing field of research into the effects, origins, and impact of earthquakes run by computer simulations, including one on the world's fastest supercomputer, Fugaku.

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