麻豆传媒

News — The surface of Earth’s inner core may be changing, as shown by a new study led by . and University of Utah scientists that detected structural changes near the planet’s center, published Monday in .

The changes of the inner core have long been a topic of debate for scientists. However, most research has been focused on assessing rotation. , Dean’s Professor of Earth Sciences at the USC Dornsife College of Letters, Arts and Sciences and principal investigator of the study, said the researchers “didn’t set out to define the physical nature of the inner core.”

“What we ended up discovering is evidence that the near surface of Earth’s inner core undergoes structural change,” Vidale said. The finding sheds light on the role topographical activity plays in rotational changes in the inner core that have minutely altered the length of a day and may relate to the ongoing slowing of the inner core.

Redefining the inner core

Located 3,000 miles below the Earth’s surface, the inner core is anchored by gravity within the molten liquid outer core. Until now the inner core was widely thought of as a solid sphere.

The original aim of the research team, which included U seismologist , was to further chart . Their previous findings used seismic data to document how the in relation to Earth’s rotation, which may be slightly altering the length of a day.

“We found that there were some very subtle differences in these seismic waves interacting with the boundary of the inner core that are pretty shallow, that sample just the top of the inner core,” said Koper, a professor in Utah’s Department of Geology & Geophysics. “Because we had established already that the inner core is librating and then we found it back in the same spot, then these differences couldn’t be due to just the change in rotation. It must be a new thing.”

That new thing appears to be alterations in the core’s shape, according to the new study.

“As I was analyzing multiple decades’ worth of seismograms, one dataset of seismic waves curiously stood out from the rest,” Vidale said. “Later on, I’d realize I was staring at evidence the inner core is not solid.”

The study utilized seismic waveform data — including 121 repeating earthquakes from 42 locations near Antarctica’s South Sandwich Islands between 1991 and 2024—to give a glimpse of what takes place in the inner core. As the researchers analyzed the waveforms from receiver-array stations located near Fairbanks, Alaska, and Yellowknife, Canada, one dataset of seismic waves from the latter station included uncharacteristic properties the team had never seen before.

“At first the dataset confounded me,” Vidale said. It wasn’t until his research team improved the resolution technique did it become clear the seismic waveforms represented additional physical activity of the inner core.

Deformed inner core

The physical activity is best explained as temporal changes in the shape of the inner core. The new study indicates that the near surface of the inner core may undergo viscous deformation, changing its shape and shifting at the inner core’s shallow boundary.

“It’s a relatively minor thing on a planetary scale, but it’s just amazing,” Koper said. “Probably the best idea is the outer core is flowing around like a big ocean,” Koper said.“It’s not super strong, but you could just imagine how the ocean leaves different patterns in the sand at the bottom of the sea. It’s probably something like that that is going on, but nobody really knows. That’s just an idea. We need to have more observations over longer amounts of time to really pin this down.”

The most likely cause of the structural change is the interaction between the inner core and outer core.

“The molten outer core is widely known to be turbulent, but its turbulence had not been observed to disrupt its neighbor the inner core on a human timescale,” Vidale said. “What we’re observing in this study for the first time is likely the outer core disturbing the inner core.”
Vidale said the discovery opens a door to reveal previously hidden dynamics deep within Earth’s core, and may lead to better understanding of Earth’s thermal and magnetic fields.

In addition to Vidale and Koper, other study authors include Ruoyan Wang of USC Dornsife, Wei Wang of the Chinese Academy of Sciences, Guanning Pang of Cornell University.

This research was supported by the National Science Foundation (EAR-2041892), the National Natural Science Foundation of China (42394114), the National Key R&D Program of China (Grant 2022YFF0503203) and the Key Research Program of the Institute of Geology & Geophysics (IGGCAS-201904, IGGCAS-202204).