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Title: Seismic anisotropy in the Earth's innermost inner core: Testing structural models against mineral physics predictions

Abstract

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. Fast axis of anisotropy in the central part of the inner core aligned with Earth's axis of rotation Lastly, the structure of iron in the inner core is most likely hcp, not bcc Not currently possible to distinguish between hcp and bcc structures from seismic observations

Authors:
 [1];  [2];  [2];  [2];  [3];  [2]
  1. Univ. of California, Berkeley, CA (United States); Institut de Physique du Globe, Paris (France)
  2. Univ. of California, Berkeley, CA (United States)
  3. Institut de Physique du Globe, Paris (France)
Publication Date:
Research Org.:
Carnegie Institution of Washington, Washington, DC (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1338341
Grant/Contract Number:  
NA0002006
Resource Type:
Accepted Manuscript
Journal Name:
Geophysical Research Letters
Additional Journal Information:
Journal Volume: 43; Journal Issue: 1; Journal ID: ISSN 0094-8276
Publisher:
American Geophysical Union
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; elasticity of iron; inner core anisotropy

Citation Formats

Romanowicz, Barbara, Cao, Aimin, Godwal, Budhiram, Wenk, Rudy, Ventosa, Sergi, and Jeanloz, Raymond. Seismic anisotropy in the Earth's innermost inner core: Testing structural models against mineral physics predictions. United States: N. p., 2016. Web. doi:10.1002/2015GL066734.
Romanowicz, Barbara, Cao, Aimin, Godwal, Budhiram, Wenk, Rudy, Ventosa, Sergi, & Jeanloz, Raymond. Seismic anisotropy in the Earth's innermost inner core: Testing structural models against mineral physics predictions. United States. doi:10.1002/2015GL066734.
Romanowicz, Barbara, Cao, Aimin, Godwal, Budhiram, Wenk, Rudy, Ventosa, Sergi, and Jeanloz, Raymond. Wed . "Seismic anisotropy in the Earth's innermost inner core: Testing structural models against mineral physics predictions". United States. doi:10.1002/2015GL066734. https://www.osti.gov/servlets/purl/1338341.
@article{osti_1338341,
title = {Seismic anisotropy in the Earth's innermost inner core: Testing structural models against mineral physics predictions},
author = {Romanowicz, Barbara and Cao, Aimin and Godwal, Budhiram and Wenk, Rudy and Ventosa, Sergi and Jeanloz, Raymond},
abstractNote = {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. Fast axis of anisotropy in the central part of the inner core aligned with Earth's axis of rotation Lastly, the structure of iron in the inner core is most likely hcp, not bcc Not currently possible to distinguish between hcp and bcc structures from seismic observations},
doi = {10.1002/2015GL066734},
journal = {Geophysical Research Letters},
number = 1,
volume = 43,
place = {United States},
year = {2016},
month = {1}
}

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Cited by: 7 works
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