Powerful quakes reveal 'heterogeneous' inner core, defying popular theories
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Powerful quakes reveal 'heterogeneous' inner core, defying popular theories

May 18, 2023


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For the first time, scientists have confirmed that the entirety of Earth's inner core is inhomogeneous— is not uniform or identical in its composition or structure — according to a new study published in Nature on July 5.

This discovery, aided by seismic data, provides valuable insights into understanding the complex nature of Earth's deepest reaches.

Earth's inner core, measuring approximately 2,442 kilometers, accounts for less than 1 percent of the Earth's total volume. Yet, its presence is crucial for the planet's magnetic field, without which Earth would be a much different place.

The formation, growth, and evolution of the inner core throughout history remain a mystery. A team of researchers from the University of Utah is investigating this enigma by studying seismic waves generated by natural earthquakes.

In 1936, seismic waves provided the initial evidence that the Earth's inner core was solid. This discovery, made by Danish seismologist Inge Lehmann, challenged the prevailing belief that the entire core was liquid due to its extremely high temperature, reaching around 10,000 degrees Fahrenheit, comparable to the sun's surface temperature.

"The inner core is not the uniform mass that scientists once believed it to be. Instead, it resembles a tapestry composed of different fabrics," said Guanning Pang, the lead author and a former Ph.D. student in the University's Department of Geology and Geophysics, in a press release.

The team tapped into special seismic arrays, including the International Monitoring System (IMS), set up worldwide to detect explosions like nuclear blasts. While the systems' primary purpose is to enforce a nuclear ban, these arrays provide valuable data for studying Earth's interior, oceans, and atmosphere.

The new research used seismic data from 20 arrays, including two in Antarctica and one near Utah. These consisted of instruments placed in boreholes drilled up to 10 meters deep in granite formations, arranged in patterns to enhance the signals they capture, similar to parabolic antennae.

Guanning Pang, the lead author, analyzed seismic waves from 2,455 earthquakes exceeding magnitude 5.7. By studying how these waves interacted with the Earth's inner core, they were able to map its internal structure.

The U team discovered valuable hints from the seismic data, revealing a 'scattering effect' associated with waves that penetrated the core's interior.

"Our biggest discovery is that inhomogeneity tends to be stronger when you get deeper. Toward the center of the Earth, it tends to be stronger," highlighted Pang.

"We think that this fabric is related to how fast the inner core was growing. A long time ago, the inner core grew really fast. It reached an equilibrium, and then it started to grow much more slowly," said U seismologist Keith Koper, who oversaw the study.

"Not all of the iron became solid, so some liquid iron could be trapped inside."

The complete study was published in Nature on July 5 and can be found here.

How do earthquakes reveal details about Earth's interior?'Inhomogeneity tends to be stronger when you get deeper'