Support for anisotropy of the Earth's inner core from free oscillations

@article{Tromp1993SupportFA,
  title={Support for anisotropy of the Earth's inner core from free oscillations},
  author={Jeroen Tromp},
  journal={Nature},
  year={1993},
  volume={366},
  pages={678-681}
}
  • J. Tromp
  • Published 1 December 1993
  • Geology
  • Nature
IN 1983, Poupinet et al.1 observed that compressional seismic waves traversing the inner core along a trajectory parallel to the Earth's rotation axis arrive faster than the same (PKIKP) waves travelling in the equatorial plane. They interpreted this observation as revealing prolate topography of the inner-core boundary. In 1986, Morelli et al.2 and Woodhouse et al.3 suggested that inner-core anisotropy could explain both the travel-time observations and the anomalous splitting of some of the… 

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TLDR
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TLDR
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Depth dependence of anisotropy of Earth's inner core

Both body wave (PKP) travel times (Creager, 1992; Song and Helmberger, 1993a; McSweeney and Creager, 1993; Shearer, 1994) and fits to the splitting of core modes (Tromp, 1993) show general agreement

The observation of inner core shear waves

Summary Although the Earth’s inner core has long been thought to be solid, there have not, as yet, been unequivocal observations of inner core shear waves. Here we present observations of the

Hemispherical variations in seismic velocity at the top of the Earth's inner core

TLDR
These residuals show no correlation with the angle at which the waves traverse the inner core, indicating that seismic anisotropy is not strong in this region and that the isotropic seismic velocity of the eastern hemisphere is about 0.8% higher than that of the western hemisphere.

Hemispherical anisotropic patterns of the Earth’s inner core

TLDR
It is shown that the data collected are in good agreement with the presence of two anisotropically specular east and west core hemispheres, compelling evidence for the existence of a body-centered-cubic Fe phase at the top of the Earth’s inner core.
...

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