Elastic and attenuation anisotropy in directionally solidified (hcp) zinc, and the seismic anisotropy in the Earth's inner core

Details Elastic and attenuation anisotropy in directionally solidified (hcp) zinc, and the seismic anisotropy in the Earth's inner core Elastic and attenuation anisotropy in directionally solidified (hcp) zinc, and the seismic anisotropy in the Earth's inner core

Jan 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000pepi..117..139b&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 117, Issue 1-4, p. 139-151.

Physics

4

Scientific paper

The inner core of the Earth has been interpreted as being elastically anisotropic, with the direction parallel to the rotation axis fast. There are also observations that north-south rays exhibit greater amplitude reduction and more complex waveforms. In previous work, we found that directionally solidified, polycrystalline, tin (Sn)-rich alloys exhibit a solidification texturing that is measurable ultrasonically, and suggested that such texturing might be a cause for the observed seismic elastic anisotropy. Here, we find that zinc (Zn)-rich alloys also exhibit a measurable elastic anisotropy that is due to a preferred growth direction. We confirm the grain orientation by back-reflection X-ray diffraction. Zn solidifies as a hexagonal closest-packed (hcp) metal, albeit one with a c/a ratio greater than the ideal, unlike hcp iron (Fe), and is 60% elastically anisotropic. We also find that the columnar dendritic grains that grow with a preferred orientation during directional solidification result in anisotropic scattering off grain boundaries, yielding an anisotropic apparent attenuation. In addition, we present results for directionally solidified 100% Zn, which exhibits qualitative differences in both the elastic and attenuation anisotropy from Zn alloys. The laboratory results can be interpreted as a cause for both the seismic elastic and attenuation anisotropy if the cooling near the inner core has more nearly cylindrical than spherical symmetry.

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