Phys.org June 12, 2024
The inner core structure influences the pattern of outer core convection and therefore Earth’s magnetic field. A team of researchers in the US (University of Southern California, Cornell University, University of Utah) compiled 143 distinct pairs of repeating earthquakes built from 121 earthquakes between 1991 and 2023 in the South Sandwich Islands. They analysed their inner-core-penetrating PKIKP waves recorded on the medium-aperture arrays in northern North America. They showed that many multiplets exhibit waveforms that change and then revert at later times to match earlier events. The matching waveforms revealed times at which the inner core re-occupies the same position, relative to the mantle, as it did at some time in the past. The pattern of matches demonstrated that the inner core gradually super-rotated from 2003 to 2008, and then from 2008 to 2023 sub-rotated two to three times more slowly back through the same path. These matches enabled precise and unambiguous tracking of inner core progression and regression. The resolved different rates of forward and backward motion suggested that new models will be necessary for the dynamics between the inner core, outer core and mantle… read more. Open Access TECHNICAL ARTICLE
Seismic ray paths and event locations. Credit: Nature, 12 June 2024