The inner core of the Earth has been a subject of study for decades, especially since the discovery of changing seismograms of repeating earthquakes. Scientists have long believed that the inner core undergoes a steady super-rotation, with changes in arrival times of seismic waves indicating a rotation rate of about 0.05–0.15° per year. Recent observations, however, have suggested more complex and fluctuating motion patterns, including oscillations.
To further understand these changes, researchers have analyzed seismic data from two seismic arrays in northern North America, focusing on waves from earthquakes in the South Sandwich Islands. By examining repeating earthquakes from 1991 to 2023, scientists have identified changes in the waveform of seismic waves, particularly PKIKP waves, which travel through the inner core.
The study revealed that many PKIKP waves showed changes over the years, indicating a rotating inner core. By comparing waveform changes over different time intervals, researchers were able to construct a model that suggests a reversing inner core motion. The analysis also showed that the rotation of the inner core has been slowing down over the years and that the motion is more complicated than previously thought.
These findings provide significant insights into the dynamics of the Earth’s inner core, showing that it is not just a solid body but undergoes complex and reversible motion. The study opens up new possibilities for understanding the processes happening deep within the Earth and may lead to further advancements in monitoring and modeling the inner core’s behavior. By continuing to analyze seismic data from different regions and time periods, scientists hope to gain a better understanding of the inner workings of our planet and the forces that drive its motion.