[Rockhounds] Up-to-fivefold reverberating waves through the Earth’s center and distinctly anisotropic innermost inner core

[Kreigh Tomaszewski]

Probing the Earth’s center is critical for understanding planetary
formation and evolution. However, geophysical inferences have been
challenging due to the lack of seismological probes sensitive to the
Earth’s center. Here, by stacking waveforms recorded by a growing number of
global seismic stations, we observe up-to-fivefold reverberating waves from
selected earthquakes along the Earth’s diameter. Differential travel times
of these exotic arrival pairs, hitherto unreported in seismological
literature, complement and improve currently available information. The
inferred transversely isotropic inner-core model contains a ~650-km thick
innermost ball with P-wave speeds ~4% slower at ~50° from the Earth’s
rotation axis. In contrast, the inner core’s outer shell displays much
weaker anisotropy with the slowest direction in the equatorial plane. Our
findings strengthen the evidence for an anisotropically-distinctive
innermost inner core and its transition to a weakly anisotropic outer
shell, which could be a fossilized record of a significant global event
from the past.

https://www.nature.com/articles/s41467-023-36074-2