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Yu C, Goes S, Day EA, van der Hilst RD. Seismic evidence for global basalt accumulation in the mantle transition zone. SCIENCE ADVANCES 2023; 9:eadg0095. [PMID: 37256943 PMCID: PMC10413675 DOI: 10.1126/sciadv.adg0095] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/26/2022] [Accepted: 04/21/2023] [Indexed: 06/02/2023]
Abstract
The mantle's compositional structure reflects the thermochemical evolution of Earth. Yet, even the radial average composition of the mantle remains debated. Here, we analyze a global dataset of shear and compressional waves reflecting off the 410- and 660-km discontinuities that is 10 times larger than any previous studies. Our array analysis retrieves globally averaged amplitude-distance trends in SS and PP precursor reflectivity from which we infer relative wavespeed and density contrasts and associated mantle composition. Our results are best matched by a basalt-enriched mantle transition zone, with higher basalt fractions near 660 (~40%) than 410 (~18-31%). These are consistent with mantle-convection/plate-recycling simulations, which predict that basaltic crust accumulates in the mantle transition zone, with basalt fractions peaking near the 660. Basalt segregation in the mantle transition zone also implies that the overall mantle is more silica enriched than the often-assumed pyrolitic mantle reference composition.
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Affiliation(s)
- Chunquan Yu
- Department of Earth and Space Sciences, Southern University of Science and Technology, Shenzhen 518055, China
- Guangdong Provincial Key Laboratory of Geophysical High-resolution Imaging Technology, Southern University of Science and Technology, Shenzhen 518055, China
| | - Saskia Goes
- Department of Earth Science and Engineering, Imperial College London, London SW7 2BP, UK
| | - Elizabeth A. Day
- Department of Earth Science and Engineering, Imperial College London, London SW7 2BP, UK
| | - Robert D. van der Hilst
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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2
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Zhang Z, Irving JCE, Simons FJ, Alkhalifah T. Seismic evidence for a 1000 km mantle discontinuity under the Pacific. Nat Commun 2023; 14:1714. [PMID: 36973245 PMCID: PMC10042893 DOI: 10.1038/s41467-023-37067-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2022] [Accepted: 02/21/2023] [Indexed: 03/29/2023] Open
Abstract
Seismic discontinuities in the mantle are indicators of its thermo-chemical state and offer clues to its dynamics. Ray-based seismic methods, though limited by the approximations made, have mapped mantle transition zone discontinuities in detail, but have yet to offer definitive conclusions on the presence and nature of mid-mantle discontinuities. Here, we show how to use a wave-equation-based imaging method, reverse-time migration of precursors to surface-reflected seismic body waves, to uncover both mantle transition zone and mid-mantle discontinuities, and interpret their physical nature. We observe a thinned mantle transition zone southeast of Hawaii, and a reduction in impedance contrast around 410 km depth in the same area, suggesting a hotter-than-average mantle in the region. Here, we furthermore reveal a 4000-5000 km-wide reflector in new images of the mid mantle below the central Pacific, at 950-1050 km depth. This deep discontinuity exhibits strong topography and generates reflections with polarity opposite to those originating at the 660 km discontinuity, implying an impedance reversal near 1000 km. We link this mid-mantle discontinuity to the upper reaches of deflected mantle plumes upwelling in the region. Reverse-time migration full-waveform imaging is a powerful approach to imaging Earth's interior, capable of broadening our understanding of its structure and dynamics and shrinking modeling uncertainties.
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Affiliation(s)
- Zhendong Zhang
- Department of Geosciences, Princeton University, Princeton, NJ, USA.
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA.
| | | | | | - Tariq Alkhalifah
- Earth Science and Engineering Program, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia
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3
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Abstract
Seismic data reveal kilometer-scale topography of the lower-mantle boundary
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Affiliation(s)
- Christine Houser
- Earth-Life Science Institute, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo 152-8550, Japan.
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4
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Wu W, Ni S, Irving JCE. Inferring Earth's discontinuous chemical layering from the 660-kilometer boundary topography. Science 2019; 363:736-740. [PMID: 30765566 DOI: 10.1126/science.aav0822] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2018] [Accepted: 01/02/2019] [Indexed: 11/02/2022]
Abstract
Topography, or depth variation, of certain interfaces in the solid Earth can provide important insights into the dynamics of our planet interior. Although the intermediate- and long-range topographic variation of the 660-kilometer boundary between Earth's upper and lower mantle is well studied, small-scale measurements are far more challenging. We found a surprising amount of topography at short length scale along the 660-kilometer boundary in certain regions using scattered P'P' seismic waves. Our observations required chemical layering in regions with high short-scale roughness. By contrast, we did not see such small-scale topography along the 410-kilometer boundary in the upper mantle. Our findings support the concept of partially blocked or imperfect circulation between the upper and lower mantle.
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Affiliation(s)
- Wenbo Wu
- State Key Laboratory of Geodesy and Earth's Dynamics, Institute of Geodesy and Geophysics, Chinese Academy of Sciences, Wuhan 430077, China.,Department of Geosciences, Princeton University, Princeton, NJ 08544, USA.,School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China
| | - Sidao Ni
- State Key Laboratory of Geodesy and Earth's Dynamics, Institute of Geodesy and Geophysics, Chinese Academy of Sciences, Wuhan 430077, China.
| | - Jessica C E Irving
- Department of Geosciences, Princeton University, Princeton, NJ 08544, USA
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Koroni M, Paulssen H, Trampert J. Sensitivity Kernels of PP Precursor Traveltimes and Their Limitations for Imaging Topography of Discontinuities. GEOPHYSICAL RESEARCH LETTERS 2019; 46:698-707. [PMID: 31007307 PMCID: PMC6472573 DOI: 10.1029/2018gl081592] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/07/2018] [Accepted: 12/12/2018] [Indexed: 06/09/2023]
Abstract
We analyze the sensitivity of PP precursor traveltimes that are often used to infer lateral variation in the depths of the 410- and 660-km discontinuities in the mantle. Previous results were inconclusive due to complex wave phenomena, such as multiple energy conversions and focusing/defocusing, that hamper their interpretation. Using spectral-element synthetics and Fréchet derivatives calculated with adjoint methods, we compute sensitivity kernels for volumetric and boundary parameters in a 1-D model for representative epicentral distances of past studies, and a dominant period of 11-25 s. Our results indicate that the boundary sensitivity of PP precursors is low and that these phases are not coherently seen in exact synthetics. Our most important finding is the strong sensitivity to both shear and compressional wave speeds, indicating that wave interference and wave conversions are dominant. The PP precursor traveltimes appear more sensitive to structural parameters, that is, compressional and shear wave speed, than to the boundaries; therefore, they are unlikely sources for valuable insight into discontinuity topography.
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Affiliation(s)
- Maria Koroni
- Department of Earth SciencesETH ZürichZürichSwitzerland
| | - Hanneke Paulssen
- Department of Earth SciencesUniversiteit UtrechtUtrechtThe Netherlands
| | - Jeannot Trampert
- Department of Earth SciencesUniversiteit UtrechtUtrechtThe Netherlands
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6
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Compositional heterogeneity near the base of the mantle transition zone beneath Hawaii. Nat Commun 2018; 9:1266. [PMID: 29593266 PMCID: PMC5872023 DOI: 10.1038/s41467-018-03654-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2017] [Accepted: 03/02/2018] [Indexed: 11/08/2022] Open
Abstract
Global seismic discontinuities near 410 and 660 km depth in Earth's mantle are expressions of solid-state phase transitions. These transitions modulate thermal and material fluxes across the mantle and variations in their depth are often attributed to temperature anomalies. Here we use novel seismic array analysis of SS waves reflecting off the 410 and 660 below the Hawaiian hotspot. We find amplitude-distance trends in reflectivity that imply lateral variations in wavespeed and density contrasts across 660 for which thermodynamic modeling precludes a thermal origin. No such variations are found along the 410. The inferred 660 contrasts can be explained by mantle composition varying from average (pyrolitic) mantle beneath Hawaii to a mixture with more melt-depleted harzburgite southeast of the hotspot. Such compositional segregation was predicted, from petrological and numerical convection studies, to occur near hot deep mantle upwellings like the one often invoked to cause volcanic activity on Hawaii.
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Global observations of reflectors in the mid-mantle with implications for mantle structure and dynamics. Nat Commun 2018; 9:385. [PMID: 29374158 PMCID: PMC5786065 DOI: 10.1038/s41467-017-02709-4] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2017] [Accepted: 12/20/2017] [Indexed: 11/11/2022] Open
Abstract
Seismic tomography indicates that flow is commonly deflected in the mid-mantle. However, without a candidate mineral phase change, causative mechanisms remain controversial. Deflection of flow has been linked to radial changes in viscosity and/or composition, but a lack of global observations precludes comprehensive tests by seismically detectable features. Here we perform a systematic global-scale interrogation of mid-mantle seismic reflectors with lateral size 500–2000 km and depths 800–1300 km. Reflectors are detected globally with variable depth, lateral extent and seismic polarity and identify three distinct seismic domains in the mid-mantle. Near-absence of reflectors in seismically fast regions may relate to dominantly subvertical heterogeneous slab material or small impedance contrasts. Seismically slow thermochemical piles beneath the Pacific generate numerous reflections. Large reflectors at multiple depths within neutral regions possibly signify a compositional or textural transition, potentially linked to long-term slab stagnation. This variety of reflector properties indicates widespread compositional heterogeneity at mid-mantle depths. The Earth’s mantle undergoes changes as temperature and pressure increase with depth. Here, the authors present a global interrogation of reflectors in the Earth’s mid-mantle revealing a significant variation in their properties, with widespread compositional heterogeneity and seismic velocity in the mid-mantle, which signify contrasting styles of mantle flow.
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First Principles Thermodynamics of Minerals at HP–HT Conditions: MgO as a Prototypical Material. MINERALS 2017. [DOI: 10.3390/min7100183] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
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9
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Rychert CA, Harmon N. Constraints on the anisotropic contributions to velocity discontinuities at ∼60 km depth beneath the Pacific. GEOCHEMISTRY, GEOPHYSICS, GEOSYSTEMS : G(3) 2017; 18:2855-2871. [PMID: 29097907 PMCID: PMC5652234 DOI: 10.1002/2017gc006850] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/03/2017] [Accepted: 06/27/2017] [Indexed: 06/07/2023]
Abstract
Strong, sharp, negative seismic discontinuities, velocity decreases with depth, are observed beneath the Pacific seafloor at ∼60 km depth. It has been suggested that these are caused by an increase in radial anisotropy with depth, which occurs in global surface wave models. Here we test this hypothesis in two ways. We evaluate whether an increase in surface wave radial anisotropy with depth is robust with synthetic resolution tests. We do this by fitting an example surface wave data set near the East Pacific Rise. We also estimate the apparent isotropic seismic velocity discontinuities that could be caused by changes in radial anisotropy in S-to-P and P-to-S receiver functions and SS precursors using synthetic seismograms. We test one model where radial anisotropy is caused by olivine alignment and one model where it is caused by compositional layering. The result of our surface wave inversion suggests strong shallow azimuthal anisotropy beneath 0-10 Ma seafloor, which would also have a radial anisotropy signature. An increase in radial anisotropy with depth at 60 km depth is not well-resolved in surface wave models, and could be artificially observed. Shallow isotropy underlain by strong radial anisotropy could explain moderate apparent velocity drops (<6%) in SS precursor imaging, but not receiver functions. The effect is diminished if strong anisotropy also exists at 0-60 km depth as suggested by surface waves. Overall, an increase in radial anisotropy with depth may not exist at 60 km beneath the oceans and does not explain the scattered wave observations.
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10
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Yu YG, Wentzcovitch RM, Vinograd VL, Angel RJ. Thermodynamic properties of MgSiO3majorite and phase transitions near 660 km depth in MgSiO3and Mg2SiO4: A first principles study. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2010jb007912] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Abstract
Abstract
Our knowledge of the structure of the Earth´s interior has been obtained by analysing seismic waves that travel in the Earth, and the reference Earth global models used by geophysicists are essentially seismological. Depth profiles of the seismic waves velocities reveal that the deep Earth is divided in several shells, separated by velocity and density discontinuities. The main discontinuity located at a depth of 2900 km corresponds to the transition between the mantle and the core. The Earth´s mantle can be further divided into the upper mantle and the lower mantle, with a transition zone characterised by two prominent increases in velocities observed at 410- and 660-km depths. This article will be focused on the mineral phases of the Earth´s mantle. The interpretation of seismological models in terms of chemical composition and temperature relies on the knowledge of the nature, structure and elastic properties of the candidate materials. We will describe to what extent recent advances in experimental mineral physics and X-ray diffraction have yielded essential knowledge on the structure and high-pressure high-temperature behaviour of pertinent materials, and major improvements in our understanding of the chemical and mineralogical composition of the Earth´s mantle.
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12
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Li B, Liebermann RC. Indoor seismology by probing the Earth's interior by using sound velocity measurements at high pressures and temperatures. Proc Natl Acad Sci U S A 2007; 104:9145-50. [PMID: 17485673 PMCID: PMC1890461 DOI: 10.1073/pnas.0608609104] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The adiabatic bulk (K(S)) and shear (G) moduli of mantle materials at high pressure and temperature can be obtained directly by measuring compressional and shear wave velocities in the laboratory with experimental techniques based on physical acoustics. We present the application of the current state-of-the-art experimental techniques by using ultrasonic interferometry in conjunction with synchrotron x radiation to study the elasticity of olivine and pyroxenes and their high-pressure phases. By using these updated thermoelasticity data for these phases, velocity and density profiles for a pyrolite model are constructed and compared with radial seismic models. We conclude that pyrolite provides an adequate explanation of the major seismic discontinuities at 410- and 660-km depths, the gradient in the transition zone, as well as the velocities in the lower mantle, if the uncertainties in the modeling and the variations in different seismic models are considered. The characteristics of the seismic scaling factors in response to thermal anomalies suggest that anticorrelations between bulk sound and shear wave velocities, as well as the large positive density anomalies observed in the lower mantle, cannot be explained fully without invoking chemical variations.
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Affiliation(s)
- Baosheng Li
- Mineral Physics Institute and Department of Geosciences, Stony Brook University, Stony Brook, NY 11790, USA.
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13
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Deuss A, Redfern SAT, Chambers K, Woodhouse JH. The Nature of the 660-Kilometer Discontinuity in Earth's Mantle from Global Seismic Observations of
PP
Precursors. Science 2006; 311:198-201. [PMID: 16410518 DOI: 10.1126/science.1120020] [Citation(s) in RCA: 124] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The 660-kilometer discontinuity, which separates Earth's upper and lower mantle, has been detected routinely on a global scale in underside reflections of precursors to SS shear waves. Here, we report observations of this discontinuity in many different regions, using precursors to compressional PP waves. The apparent absence of such precursors in previous studies had posed major problems for models of mantle composition. We find a complicated structure, showing single and double reflections ranging in depth from 640 to 720 kilometers, that requires the existence of multiple phase transitions at the base of the transition zone. The results are consistent with a pyrolite mantle composition.
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Affiliation(s)
- Arwen Deuss
- Department of Earth Sciences, University of Cambridge, Cambridge CB3 0EZ, UK.
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Chambers K, Deuss A, Woodhouse JH. Reflectivity of the 410-km discontinuity fromPPandSSprecursors. ACTA ACUST UNITED AC 2005. [DOI: 10.1029/2004jb003345] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- K. Chambers
- Department of Earth Sciences; University of Oxford; Oxford UK
| | - A. Deuss
- Institute of Theoretical Geophysics, Department of Earth Sciences; University of Cambridge; Cambridge UK
| | - J. H. Woodhouse
- Department of Earth Sciences; University of Oxford; Oxford UK
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15
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Xu F, Vidale JE, Earle PS. Survey of precursors toP′P′: Fine structure of mantle discontinuities. ACTA ACUST UNITED AC 2003. [DOI: 10.1029/2001jb000817] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Fei Xu
- Department of Earth and Space Science; University of California; Los Angeles California USA
| | - John E. Vidale
- Department of Earth and Space Science; University of California; Los Angeles California USA
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Li B, Liebermann RC, Weidner DJ. P-V-Vp-Vs-Tmeasurements on wadsleyite to 7 GPa and 873 K: Implications for the 410-km seismic discontinuity. ACTA ACUST UNITED AC 2001. [DOI: 10.1029/2001jb000317] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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17
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Multiple seismic discontinuities near the base of the transition zone in the Earth's mantle. Nature 2000; 405:559-62. [PMID: 10850712 DOI: 10.1038/35014589] [Citation(s) in RCA: 109] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The seismologically defined boundary between the transition zone in the Earth's mantle (410-660 km depth) and the underlying lower mantle is generally interpreted to result from the breakdown of the gamma-spinel phase of olivine to magnesium-perovskite and magnesiowustite. Laboratory measurements of these transformations of olivine have determined that the phase boundary has a negative Clapeyron slope and does indeed occur near pressures corresponding to the base of the transition zone. But a computational study has indicated that, because of the presence of garnet minerals, multiple seismic discontinuities might exist near a depth of 660 km (ref. 4), which would alter the simple negative correlation of changes in temperature with changes in the depth of the phase boundary. In particular, garnet minerals undergo exothermic transformations near this depth, acting to complicate the phase relations and possibly effecting mantle convection processes in some regions. Here we present seismic evidence that supports the existence of such multiple transitions near a depth of 660 km beneath southern California. The observations are consistent with having been generated by garnet transformations coupling with the dissociation of the gamma-spinel phase of olivine. Temperature anomalies calculated from the imaged discontinuity depths--using Clapeyron slopes determined for the various transformations--generally match those predicted from an independent P-wave velocity model of the region.
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Shearer PM. Upper mantle seismic discontinuities. EARTH'S DEEP INTERIOR: MINERAL PHYSICS AND TOMOGRAPHY FROM THE ATOMIC TO THE GLOBAL SCALE 2000. [DOI: 10.1029/gm117p0115] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
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