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Pang G, Koper KD, Wu SM, Wang W, Lasbleis M, Euler G. Enhanced inner core fine-scale heterogeneity towards Earth's centre. Nature 2023; 620:570-575. [PMID: 37407825 DOI: 10.1038/s41586-023-06213-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2022] [Accepted: 05/12/2023] [Indexed: 07/07/2023]
Abstract
Earth's inner core acquires texture as it solidifies within the fluid outer core. The size, shape and orientation of the mostly iron grains making up the texture record the growth of the inner core and may evolve over geologic time in response to geodynamical forces and torques1. Seismic waves from earthquakes can be used to image the texture, or fabric, of the inner core and gain insight into the history and evolution of Earth's core2-6. Here, we observe and model seismic energy backscattered from the fine-scale (less than 10 km) heterogeneities7 that constitute inner core fabric at larger scales. We use a novel dataset created from a global array of small-aperture seismic arrays-designed to detect tiny signals from underground nuclear explosions-to create a three-dimensional model of inner core fine-scale heterogeneity. Our model shows that inner core scattering is ubiquitous, existing across all sampled longitudes and latitudes, and that it substantially increases in strength 500-800 km beneath the inner core boundary. The enhanced scattering in the deeper inner core is compatible with an era of rapid growth following delayed nucleation.
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Affiliation(s)
- Guanning Pang
- Department of Geology and Geophysics, University of Utah, Salt Lake City, UT, USA.
- Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, NY, USA.
| | - Keith D Koper
- Department of Geology and Geophysics, University of Utah, Salt Lake City, UT, USA
| | - Sin-Mei Wu
- Department of Geology and Geophysics, University of Utah, Salt Lake City, UT, USA
- Swiss Seismological Service, ETH Zurich, Zurich, Switzerland
| | - Wei Wang
- Department of Earth Sciences, University of Southern California, Los Angeles, CA, USA
- Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
| | - Marine Lasbleis
- Laboratoire de Planétologie et Géosciences, UMR 6112, Université de Nantes, CNRS, Nantes, France
- Bureau Veritas Marine & Offshore, Paris La Défense, France
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Phạm TS, Tkalčić H. Up-to-fivefold reverberating waves through the Earth's center and distinctly anisotropic innermost inner core. Nat Commun 2023; 14:754. [PMID: 36810283 PMCID: PMC9944935 DOI: 10.1038/s41467-023-36074-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2022] [Accepted: 01/11/2023] [Indexed: 02/24/2023] Open
Abstract
Probing the Earth's center is critical for understanding planetary formation and evolution. However, geophysical inferences have been challenging due to the lack of seismological probes sensitive to the Earth's center. Here, by stacking waveforms recorded by a growing number of global seismic stations, we observe up-to-fivefold reverberating waves from selected earthquakes along the Earth's diameter. Differential travel times of these exotic arrival pairs, hitherto unreported in seismological literature, complement and improve currently available information. The inferred transversely isotropic inner-core model contains a ~650-km thick innermost ball with P-wave speeds ~4% slower at ~50° from the Earth's rotation axis. In contrast, the inner core's outer shell displays much weaker anisotropy with the slowest direction in the equatorial plane. Our findings strengthen the evidence for an anisotropically-distinctive innermost inner core and its transition to a weakly anisotropic outer shell, which could be a fossilized record of a significant global event from the past.
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Affiliation(s)
- Thanh-Son Phạm
- Research School of Earth Sciences, The Australian National University, Canberra, ACT, Australia.
| | - Hrvoje Tkalčić
- grid.1001.00000 0001 2180 7477Research School of Earth Sciences, The Australian National University, Canberra, ACT Australia
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Ni Doping: A Viable Route to Make Body-Centered-Cubic Fe Stable at Earth’s Inner Core. MINERALS 2021. [DOI: 10.3390/min11030258] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
With the goal of answering the highly debated question of whether the presence of Ni at the Earth’s inner core can make body-centered cubic (bcc) Fe stable, we performed a computational study based on first-principles calculations on bcc, hexagonal closed packed (hcp), and face-centered cubic (fcc) structures of the Fe1−xNix alloys (x = 0, 0.0312, 0.042, 0.0625, 0.084, 0.125, 0.14, 0.175) at 200–364 GPa and investigated their relative stability. Our thorough study reveals that the stability of Ni-doped bcc Fe is crucially dependent on the nature of the distribution of Ni in the Fe matrix. We confirm this observation by considering several possible configurations for a given concentration of Ni doping. Our theoretical evidence suggests that Ni-doped bcc Fe could be a stable phase at the Earth’s inner core condition as compared to its hcp and fcc counterparts.
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Waszek L, Deuss A. Distinct layering in the hemispherical seismic velocity structure of Earth's upper inner core. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2011jb008650] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Irving JCE, Deuss A. Hemispherical structure in inner core velocity anisotropy. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2010jb007942] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Mattesini M, Belonoshko AB, Buforn E, Ramírez M, Simak SI, Udías A, Mao HK, Ahuja R. Hemispherical anisotropic patterns of the Earth's inner core. Proc Natl Acad Sci U S A 2010; 107:9507-12. [PMID: 20457937 PMCID: PMC2906852 DOI: 10.1073/pnas.1004856107] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
It has been shown that the Earth's inner core has an axisymmetric anisotropic structure with seismic waves traveling approximately 3% faster along polar paths than along equatorial directions. Hemispherical anisotropic patterns of the solid Earth's core are rather complex, and the commonly used hexagonal-close-packed iron phase might be insufficient to account for seismological observations. We show that the data we collected are in good agreement with the presence of two anisotropically specular east and west core hemispheres. The detected travel-time anomalies can only be disclosed by a lattice-preferred orientation of a body-centered-cubic iron aggregate, having a fraction of their [111] crystal axes parallel to the Earth's rotation axis. This is compelling evidence for the presence of a body-centered-cubic Fe phase at the top of the Earth's inner core.
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Affiliation(s)
- Maurizio Mattesini
- Departamento de Física de la Tierra, Astronomía y Astrofísica I, Universidad Complutense de Madrid, E-28040 Madrid, Spain.
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Deuss A, Irving JCE, Woodhouse JH. Regional Variation of Inner Core Anisotropy from Seismic Normal Mode Observations. Science 2010; 328:1018-20. [DOI: 10.1126/science.1188596] [Citation(s) in RCA: 104] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- Arwen Deuss
- Department of Earth Sciences, University of Cambridge, Cambridge CB3 0EZ, UK
| | | | - John H. Woodhouse
- Department of Earth Sciences, University of Oxford, Oxford OX1 3PR, UK
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Wookey J, Helffrich G. Inner-core shear-wave anisotropy and texture from an observation of PKJKP waves. Nature 2008; 454:873-6. [PMID: 18704084 DOI: 10.1038/nature07131] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2007] [Accepted: 05/28/2008] [Indexed: 11/09/2022]
Abstract
Since the discovery of the Earth's core a century ago, and the subsequent discovery of a solid inner core (postulated to have formed by the freezing of iron) seismologists have striven to understand this most remote part of the deep Earth. The most direct evidence for a solid inner core would be the observation of shear-mode body waves that traverse it, but these phases are extremely difficult to observe. Two reported observations in short-period data have proved controversial. Arguably more successful have been studies of longer-period data, but such averaging limits the usefulness of the observations to reported sightings. We present two observations of an inner-core shear-wave phase at higher frequencies in stacked data from the Japanese High-Sensitivity Array, Hi-Net. From an analysis of timing, amplitude and waveform of the 'PKJKP' phase we derive constraints on inner-core compressional-wave velocity and shear attenuation at about 0.3 Hz which differ from standard isotropic core models. We can explain waveform features and can partially reconcile the otherwise large differences between core wavespeed and attenuation models that our observations apparently suggest if we invoke shear-wave anisotropy in the inner core. A simple model of an inner core composed of hexagonal close-packed iron with its c axis aligned perpendicular to the rotation axis yields anisotropy that is compatible with both the shear-wave anisotropy that we observe and the well-established 3 per cent compressional-wave anisotropy.
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Affiliation(s)
- James Wookey
- Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, BS8 1RJ, UK.
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Belonoshko AB, Skorodumova NV, Rosengren A, Johansson B. Elastic Anisotropy of Earth's Inner Core. Science 2008; 319:797-800. [DOI: 10.1126/science.1150302] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- Anatoly B. Belonoshko
- Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, SE-100 44 Stockholm, Sweden
- Condensed Matter Theory, Department of Theoretical Physics, AlbaNova University Center, Royal Institute of Technology, SE-106 91 Stockholm, Sweden
- Condensed Matter Theory Group, Department of Physics, Uppsala University, Uppsala Box 530, Sweden
- NORDITA, AlbaNova University Center, SE-106 91 Stockholm, Sweden
- School of Physics and Optoelectronic Technology and College of Advanced Science and Technology, Dalian University of Technology, Dalian 116024, China
| | - Natalia V. Skorodumova
- Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, SE-100 44 Stockholm, Sweden
- Condensed Matter Theory, Department of Theoretical Physics, AlbaNova University Center, Royal Institute of Technology, SE-106 91 Stockholm, Sweden
- Condensed Matter Theory Group, Department of Physics, Uppsala University, Uppsala Box 530, Sweden
- NORDITA, AlbaNova University Center, SE-106 91 Stockholm, Sweden
- School of Physics and Optoelectronic Technology and College of Advanced Science and Technology, Dalian University of Technology, Dalian 116024, China
| | - Anders Rosengren
- Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, SE-100 44 Stockholm, Sweden
- Condensed Matter Theory, Department of Theoretical Physics, AlbaNova University Center, Royal Institute of Technology, SE-106 91 Stockholm, Sweden
- Condensed Matter Theory Group, Department of Physics, Uppsala University, Uppsala Box 530, Sweden
- NORDITA, AlbaNova University Center, SE-106 91 Stockholm, Sweden
- School of Physics and Optoelectronic Technology and College of Advanced Science and Technology, Dalian University of Technology, Dalian 116024, China
| | - Börje Johansson
- Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, SE-100 44 Stockholm, Sweden
- Condensed Matter Theory, Department of Theoretical Physics, AlbaNova University Center, Royal Institute of Technology, SE-106 91 Stockholm, Sweden
- Condensed Matter Theory Group, Department of Physics, Uppsala University, Uppsala Box 530, Sweden
- NORDITA, AlbaNova University Center, SE-106 91 Stockholm, Sweden
- School of Physics and Optoelectronic Technology and College of Advanced Science and Technology, Dalian University of Technology, Dalian 116024, China
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Yu WC, Wen L. Complex seismic anisotropy in the top of the Earth's inner core beneath Africa. ACTA ACUST UNITED AC 2007. [DOI: 10.1029/2006jb004868] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Leyton F, Koper KD. UsingPKiKPcoda to determine inner core structure: 2. Determination ofQC. ACTA ACUST UNITED AC 2007. [DOI: 10.1029/2006jb004370] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Yu WC, Wen L. Seismic velocity and attenuation structures in the top 400 km of the Earth's inner core along equatorial paths. ACTA ACUST UNITED AC 2006. [DOI: 10.1029/2005jb003995] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Koper KD. Observations ofPKiKP/PcPamplitude ratios and implications for Earth structure at the boundaries of the liquid core. ACTA ACUST UNITED AC 2004. [DOI: 10.1029/2003jb002750] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Vocadlo L, Alfè D, Gillan MJ, Wood IG, Brodholt JP, Price GD. Possible thermal and chemical stabilization of body-centred-cubic iron in the Earth's core. Nature 2003; 424:536-9. [PMID: 12891353 DOI: 10.1038/nature01829] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2002] [Accepted: 06/18/2003] [Indexed: 11/09/2022]
Abstract
The nature of the stable phase of iron in the Earth's solid inner core is still highly controversial. Laboratory experiments suggest the possibility of an uncharacterized phase transformation in iron at core conditions and seismological observations have indicated the possible presence of complex, inner-core layering. Theoretical studies currently suggest that the hexagonal close packed (h.c.p.) phase of iron is stable at core pressures and that the body centred cubic (b.c.c.) phase of iron becomes elastically unstable at high pressure. In other h.c.p. metals, however, a high-pressure b.c.c. form has been found to become stabilized at high temperature. We report here a quantum mechanical study of b.c.c.-iron able to model its behaviour at core temperatures as well as pressures, using ab initio molecular dynamics free-energy calculations. We find that b.c.c.-iron indeed becomes entropically stabilized at core temperatures, but in its pure state h.c.p.-iron still remains thermodynamically more favourable. The inner core, however, is not pure iron, and our calculations indicate that the b.c.c. phase will be stabilized with respect to the h.c.p. phase by sulphur or silicon impurities in the core. Consequently, a b.c.c.-structured alloy may be a strong candidate for explaining the observed seismic complexity of the inner core.
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Affiliation(s)
- Lidunka Vocadlo
- Research School of Earth Sciences, Birkbeck College and University College London, UK.
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Affiliation(s)
- Malcolm Sambridge
- Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia.
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