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Our planet is far from a dead piece of rock. Inside there is a liquid core and a viscous mantle, but the center is considered solid. But there are also inhomogeneities in it, and most importantly, its behavior is alarming. The fact is that the rotation speed of the inner core changes over several years. This was established by recording seismic waves from recurring earthquakes. In recent years, the rotation of the inner core has either accelerated or slowed down relative to the rotation of the rest of the planet's mass. In a new study, scientists re-analyzed data obtained over the past 20 years and discovered an anomaly near the boundary of the two parts of the core.
The Earth's core is mostly liquid, but inside it contains a solid part that grows over geological time. The inner core plays a large role in thermal convection and the formation of our planet's magnetic field. It is studied using seismic waves generated by earthquakes.
For decades, geologists have been arguing that the seismograms of recurring earthquakes are changing. More and more data suggests that the cause lies in the inner core. According to the latest models, it slowed down or even changed direction of rotation around 2010.
Scientists led by John Vidal from the University of South Carolina (USA) took data on earthquakes that occurred from 1991 to 2024 in the area of the South Sandwich Islands, near Antarctica. And they were registered by two groups of seismographs in Alaska and Canada. In total - 168 repeating pairs of earthquakes in 42 places. The researchers were interested in PKIKP waves that cross the core. Initially, they wanted to map the slowdown in the rotation speed of the inner core, but made a discovery. The article with the results of the study was published in the journal Nature Geoscience.
"We found that the surface layer of the inner core is undergoing structural changes," Vidal commented.
The authors of the scientific work analyzed data on pairs of earthquakes that occurred at the same time when the core, having turned around, returned to the same position, which means that the differences in seismic waves could not be explained by the difference in the speed of rotation. Then anomalies appeared in the data set from Canada. The fact is that they record waves that only affect the inner core, and do not cross it. The properties of the latter are constant, while the former changed. All this indicated unusual physical activity near the boundary of the inner and outer cores.
The simplest explanation is temporary changes in the shape of the inner core. Thus, scientists have resolved a long-standing dispute about what causes the temporal variability of PKIKP waves - rotation or physical activity in the inner core. Previously, it was believed that both anomalies could not occur simultaneously. Now it turns out that, apparently, they can. What the researchers saw is most likely signs of viscous deformation caused by the influence of the outer core or mantle.
