A mystery is building deep inside the Earth's core. For decades, scientists have been aware of this mismatch, known as seismic anisotropy, but have been unable to come up with an explanation that is compatible with the facts.
Seismic Waves in the Core
Seismic waves (subterranean shocks caused by earthquakes) traveling through the planet's solid iron inner core are the only way scientists can detect it. Waves going between the north and south poles flow through the core at a substantially higher rate than waves moving across the equator for some reason.
Recent research published in the June 3 edition of Nature Geoscience uses computer models of the core's evolution over the last billion years to give an answer that finally appears to fit: Every year, Earth's inner core grows in a "lopsided" pattern, with new iron crystals accumulating quicker on the east side than on the west.
According to senior research author Daniel Frost, a seismologist at the University of California, Berkeley, "the flow of liquid iron in the outer core transports heat away from the inner core, causing it to freeze." "This suggests that the outer core has been absorbing more heat from the east side [under Indonesia] than from the west side [under Brazil]."
Imagine a tree trunk with growth rings spreading out from a central point, but "the center of the rings is offset from the center of the tree," thus rings are spaced further apart on the east side of the tree and closer together on the west side, according to Frost.
Related Article: What Exactly Causes Mysterious Deep Earthquakes?
However, the asymmetric development does not imply that the inner core is misshaped or at risk of becoming unbalanced, according to the researchers.
Every year, the radius of the inner core expands by around 0.04 inches (1 millimeter) on average. Gravity compensates for the east's unbalanced growth by forcing fresh crystals westward.
The crystals cluster together and form lattice structures that run the length of the core's north-south axis. According to the team's models, these crystal formations lined parallel to Earth's poles are seismic superhighways that allow earthquake waves to move faster in that direction.
What is Responsible?
Tectonic plates, according to Frost, may be partially to blame. At subduction zones (places where one plate descends underneath another), frigid tectonic plates descend far beneath the Earth's surface, cooling the mantle below. However, whether mantle cooling influences the inner core is still up for discussion, according to Frost.
It's also unclear if the asymmetrical cooling in the core is altering the Earth's magnetic field. The current magnetic field is driven by the flow of liquid iron in the outer core, which is driven by heat lost from the inner core. So, if the inner core loses more heat in the east than in the west, the outer core will shift east as well.
He went on to say, "The question is, does this affect the intensity of the magnetic field?"
These are questions outside the scope of the team's recent article, but Frost said he has started working on new research with a group of geomagnetic researchers to look at potential possibilities.
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