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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 Inst. 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. https://doi.org/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. https://doi.org/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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Works referenced in this record:

Iron under Earth’s core conditions: Liquid-state thermodynamics and high-pressure melting curve from ab initio calculations
journal, April 2002


Melting of Iron at Earth's Inner Core Boundary Based on Fast X-ray Diffraction
journal, April 2013


Robust Normal Mode Constraints on Inner-Core Anisotropy from Model Space Search
journal, January 2003


Stability of the body-centred-cubic phase of iron in the Earth's inner core
journal, August 2003

  • Belonoshko, Anatoly B.; Ahuja, Rajeev; Johansson, Börje
  • Nature, Vol. 424, Issue 6952
  • DOI: 10.1038/nature01954

Stability of the body-centered-tetragonal phase of Fe at high pressure: Ground-state energies, phonon spectra, and molecular dynamics simulations
journal, December 2006


Origin of the Low Rigidity of the Earth's Inner Core
journal, June 2007


Elastic Anisotropy of Earth's Inner Core
journal, February 2008


Ab initio equation of state of iron up to 1500 GPa
journal, March 2013


The equation of state of iron to 450 GPa: Another high pressure solid phase?
journal, November 2001


Phase transitions, Grüneisen parameter, and elasticity for shocked iron between 77 GPa and 400 GPa
journal, June 1986

  • Brown, J. Michael; McQueen, Robert G.
  • Journal of Geophysical Research: Solid Earth, Vol. 91, Issue B7
  • DOI: 10.1029/JB091iB07p07485

Hugoniot data for iron
journal, November 2000

  • Brown, J. M.; Fritz, J. N.; Hixson, R. S.
  • Journal of Applied Physics, Vol. 88, Issue 9
  • DOI: 10.1063/1.1319320

Texturing of the Earth's inner core by Maxwell stresses
journal, September 2001

  • Buffett, B. A.; Wenk, H. -R.
  • Nature, Vol. 413, Issue 6851
  • DOI: 10.1038/35092543

Test of the innermost inner core models using broadband PKIKP travel time residuals: TEST OF INNERMOST INNER CORE MODELS
journal, April 2007


Waveform search for the innermost inner core
journal, July 2005

  • Cormier, Vernon F.; Stroujkova, Anastasia
  • Earth and Planetary Science Letters, Vol. 236, Issue 1-2
  • DOI: 10.1016/j.epsl.2005.05.016

Ab initio lattice dynamics calculations on the combined effect of temperature and silicon on the stability of different iron phases in the Earth's inner core
journal, January 2010

  • Côté, Alexander S.; Vočadlo, Lidunka; Dobson, David P.
  • Physics of the Earth and Planetary Interiors, Vol. 178, Issue 1-2
  • DOI: 10.1016/j.pepi.2009.07.004

Structure and dynamics of Earth's inner core
journal, June 2012


Body-Centered Cubic Iron-Nickel Alloy in Earth's Core
journal, June 2007


Phase relations in the Fe–FeSi system at high pressures and temperatures
journal, July 2013

  • Fischer, Rebecca A.; Campbell, Andrew J.; Reaman, Daniel M.
  • Earth and Planetary Science Letters, Vol. 373
  • DOI: 10.1016/j.epsl.2013.04.035

Whole-mantle radially anisotropic shear velocity structure from spectral-element waveform tomography
journal, September 2014

  • French, S. W.; Romanowicz, B. A.
  • Geophysical Journal International, Vol. 199, Issue 3
  • DOI: 10.1093/gji/ggu334

The axial ratio of hcp iron at the conditions of the Earth’s inner core
journal, September 2005

  • Gannarelli, C. M. S.; Alfè, D.; Gillan, M. J.
  • Physics of the Earth and Planetary Interiors, Vol. 152, Issue 1-2
  • DOI: 10.1016/j.pepi.2005.06.003

Stability of iron crystal structures at 0.3–1.5 TPa
journal, January 2015

  • Godwal, B. K.; González-Cataldo, F.; Verma, A. K.
  • Earth and Planetary Science Letters, Vol. 409
  • DOI: 10.1016/j.epsl.2014.10.056

Composition and State of the Core
journal, May 2013


The innermost inner core of the earth: Evidence for a change in anisotropic behavior at the radius of about 300 km
journal, October 2002

  • Ishii, M.; Dziewonski, A. M.
  • Proceedings of the National Academy of Sciences, Vol. 99, Issue 22
  • DOI: 10.1073/pnas.172508499

Convection and anisotropy of the inner core
journal, January 1988


Constraints on seismic velocities in the Earth from traveltimes
journal, July 1995


A new global model for P wave speed variations in Earth's mantle
journal, May 2008

  • Li, Chang; van der Hilst, Robert D.; Engdahl, E. Robert
  • Geochemistry, Geophysics, Geosystems, Vol. 9, Issue 5
  • DOI: 10.1029/2007GC001806

Seismic response and anisotropy of a model hcp iron inner core
journal, May 2014

  • Lincot, Ainhoa; Deguen, Renaud; Merkel, Sébastien
  • Comptes Rendus Geoscience, Vol. 346, Issue 5-6
  • DOI: 10.1016/j.crte.2014.04.001

Is inner core seismic anisotropy a marker for plastic flow of cubic iron?
journal, March 2015

  • Lincot, A.; Merkel, S.; Cardin, P.
  • Geophysical Research Letters, Vol. 42, Issue 5
  • DOI: 10.1002/2014GL062862

Strong Premelting Effect in the Elastic Properties of hcp-Fe Under Inner-Core Conditions
journal, October 2013


Hemispherical anisotropic patterns of the Earth's inner core
journal, May 2010

  • Mattesini, M.; Belonoshko, A. B.; Buforn, E.
  • Proceedings of the National Academy of Sciences, Vol. 107, Issue 21
  • DOI: 10.1073/pnas.1004856107

Deformation of polycrystalline iron up to 30GPa and 1000K
journal, July 2004

  • Merkel, Sébastien; Wenk, Hans-Rudolf; Gillet, Philippe
  • Physics of the Earth and Planetary Interiors, Vol. 145, Issue 1-4
  • DOI: 10.1016/j.pepi.2004.04.001

Stability of the hcp phase and temperature variation of the axial ratio of iron near Earth-core conditions
journal, December 2006


Anisotropy of the inner core inferred from PKIKP travel times
journal, December 1986

  • Morelli, Andrea; Dziewonski, Adam M.; Woodhouse, John H.
  • Geophysical Research Letters, Vol. 13, Issue 13
  • DOI: 10.1029/GL013i013p01545

Melting of iron at the physical conditions of the Earth's core
journal, January 2004


Solid Iron Compressed Up to 560 GPa
journal, August 2013


Stability field of the hcp-structure for Fe, Fe-Ni, and Fe-Ni-Si alloys up to 3 Mbar: FE-NI-SI ALLOY UP TO 3 MBAR
journal, May 2011

  • Sakai, Takeshi; Ohtani, Eiji; Hirao, Naohisa
  • Geophysical Research Letters, Vol. 38, Issue 9
  • DOI: 10.1029/2011GL047178

Melting and crystal structure of iron at high pressures and temperatures
journal, February 1998

  • Shen, Guoyin; Mao, Ho-kwang; Hemley, Russell J.
  • Geophysical Research Letters, Vol. 25, Issue 3
  • DOI: 10.1029/97GL03776

LLNL-G3Dv3: Global P wave tomography model for improved regional and teleseismic travel time prediction: LLNL-G3DV3---GLOBAL P WAVE TOMOGRAPHY
journal, October 2012

  • Simmons, N. A.; Myers, S. C.; Johannesson, G.
  • Journal of Geophysical Research: Solid Earth, Vol. 117, Issue B10
  • DOI: 10.1029/2012JB009525

High-Pressure Elasticity of Iron and Anisotropy of Earth's Inner Core
journal, March 1995


The Structure of Iron in Earth's Inner Core
journal, October 2010


The structure of Fe–Si alloy in Earth's inner core
journal, May 2015

  • Tateno, Shigehiko; Kuwayama, Yasuhiro; Hirose, Kei
  • Earth and Planetary Science Letters, Vol. 418
  • DOI: 10.1016/j.epsl.2015.02.008

Possible thermal and chemical stabilization of body-centred-cubic iron in the Earth's core
journal, July 2003

  • Vočadlo, Lidunka; Alfè, Dario; Gillan, M. J.
  • Nature, Vol. 424, Issue 6948
  • DOI: 10.1038/nature01829

The stability of bcc-Fe at high pressures and temperatures with respect to tetragonal strain
journal, September 2008

  • Vočadlo, Lidunka; Wood, Ian G.; Gillan, Michael J.
  • Physics of the Earth and Planetary Interiors, Vol. 170, Issue 1-2
  • DOI: 10.1016/j.pepi.2008.07.032

Ab initio calculations of the elasticity of hcp-Fe as a function of temperature at inner-core pressure
journal, November 2009

  • Vočadlo, Lidunka; Dobson, David P.; Wood, Ian G.
  • Earth and Planetary Science Letters, Vol. 288, Issue 3-4
  • DOI: 10.1016/j.epsl.2009.10.015

The Melting Curve of Iron to 250 Gigapascals: A Constraint on the Temperature at Earth's Center
journal, April 1987


The high-pressure melting curve of iron: A technical discussion
journal, January 1991

  • Williams, Quentin; Knittle, Elise; Jeanloz, Raymond
  • Journal of Geophysical Research, Vol. 96, Issue B2
  • DOI: 10.1029/90JB01999

Evidence for inner core anisotropy from free oscillations
journal, December 1986

  • Woodhouse, John H.; Giardini, Domenico; Li, Xiang-Dong
  • Geophysical Research Letters, Vol. 13, Issue 13
  • DOI: 10.1029/GL013i013p01549

Shock temperatures and melting of iron at Earth core conditions
journal, June 1993


Works referencing / citing this record:

Polymorphic Nature of Iron and Degree of Lattice Preferred Orientation Beneath the Earth's Inner Core Boundary
journal, January 2018

  • Mattesini, Maurizio; Belonoshko, Anatoly B.; Tkalčić, Hrvoje
  • Geochemistry, Geophysics, Geosystems, Vol. 19, Issue 1
  • DOI: 10.1002/2017gc007285

Irregular Transition Layer Beneath the Earth's Inner Core Boundary From Observations of Antipodal PKIKP and PKIIKP Waves
journal, October 2018

  • Attanayake, Januka; Thomas, Christine; Cormier, Vernon F.
  • Geochemistry, Geophysics, Geosystems, Vol. 19, Issue 10
  • DOI: 10.1029/2018gc007562

The influence of carbon on the seismic properties of solid iron: CARBON IN THE INNER CORE
journal, January 2017


Geophysics From Terrestrial Time-Variable Gravity Measurements: Time-Variable Gravity Measurements
journal, November 2017

  • Van Camp, Michel; de Viron, Olivier; Watlet, Arnaud
  • Reviews of Geophysics, Vol. 55, Issue 4
  • DOI: 10.1002/2017rg000566