Journal
GEOPHYSICAL RESEARCH LETTERS
Volume 43, Issue 1, Pages 93-100Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1002/2015GL066734
Keywords
inner core anisotropy; elasticity of iron
Categories
Funding
- University of California
- US Department of Energy
- European Research Council
- NSF [EAR 1343908, EAR 1417229, CSEDI-106751]
- CDAC
- Directorate For Geosciences [1417229, 1343908] Funding Source: National Science Foundation
- Division Of Earth Sciences [1343908, 1417229] Funding Source: National Science Foundation
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Using an updated data set of ballistic PKIKP travel time data at antipodal distances, we test different models of anisotropy in the Earth's innermost inner core (IMIC) and obtain significantly better fits for a fast axis aligned with Earth's rotation axis, rather than a quasi-equatorial direction, as proposed recently. Reviewing recent results on the single crystal structure and elasticity of iron at core conditions, we find that an hcp structure with the fast c axis parallel to Earth's rotation is more likely but a body-centered cubic structure with the [111] axis aligned in that direction results in very similar predictions for seismic anisotropy. These models are therefore not distinguishable based on current seismological data. In addition, to match the seismological observations, the inferred strength of anisotropy in the IMIC (6-7%) implies almost perfect alignment of iron crystals, an intriguing, albeit unlikely situation, especially in the presence of heterogeneity, which calls for further studies.
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