Recent seismic wave measurements indicate that Earth’s solid inner core may have experienced changes in shape over the past two decades. However, the behavior of these seismic waves could also be attributed to other shifts occurring at the planet’s center.
Since the 1990s, seismic measurements have suggested that the iron-nickel inner core rotates independently, with its rotation speed varying relative to the rest of the planet. These fluctuations can influence phenomena such as the length of a day.
According to experts, the changes in rotation are primarily driven by magnetic forces generated by the convective movements within Earth’s liquid outer core. This ongoing flow exerts torque on the inner core.
Furthermore, these magnetic influences—or related processes—could alter both the shape and rotation of the inner core. Some previous seismic wave measurements implied such changes, but uncertainty regarding the core’s rotation made it difficult to differentiate between alterations in rotation and those in shape.
Recent analysis by researchers involved evaluations of seismic waves generated by 128 earthquakes along the coast of South America from 1991 to 2023. The waves were recorded in Alaska after traversing the Earth.
From this data, the researchers identified 168 pairs of seismic waves that passed through or near identical locations in the inner core at different times. This analysis became possible following advancements in understanding the inner core’s rotational changes.
The seismic waves that did not pass through the inner core exhibited consistent patterns, suggesting stability in those regions. In contrast, the mismatched waves that intersected with the inner core indicated significant changes that could not merely be attributed to rotational differences.
These findings imply that the inner core not only varies its rotation over decades but may also change its shape. The researchers hypothesize that convection in the outer core could be magnetically pulling at the less viscous edge of the inner core, or that interactions with the lower mantle may play a role.
Experts note that this research represents progress in understanding the complexities of the inner core’s dynamics. However, the possibility that the observed differences in seismic waves could stem from other unrelated phenomena, such as changes within the outer core or even eruptions of molten material, cannot be ruled out. Further studies of repeat earthquakes will be vital for deeper insights.
In addition, researchers suggest that conducting more seismological measurements in remote areas like the ocean floor will be essential for comprehending Earth’s deepest interior evolution over geological time.
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