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ABSTRACT Knowledge of the seismic velocity structure at the top of the Earth's inner core is important for deciphering the physical processes responsible for inner-core growth1,2,3.
Previous global seismic studies4,5,6,7,8,9 have focused on structures found 100 km or deeper within the inner core, with results for the uppermost 100 km available for only isolated
regions10,11,12. Here we present constraints on seismic velocity variations just beneath the inner-core boundary, determined from the difference in travel time between waves reflected at the
inner-core boundary and those transmitted through the inner core. We found that these travel-time residuals—observed on both global seismograph stations and several regional seismic
networks—are systematically larger, by about 0.8 s, for waves that sample the ‘eastern hemisphere’ of the inner core (40° E to 180° E) compared to those that sample the ‘western hemisphere’
(180° W to 40° E). These residuals show no correlation with the angle at which the waves traverse the inner core; this indicates that seismic anisotropy is not strong in this region and that
the isotropic seismic velocity of the eastern hemisphere is about 0.8% higher than that of the western hemisphere. Access through your institution Buy or subscribe This is a preview of
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BOTH THE ROTATION RATE AND NEAR SURFACE OF EARTH’S INNER CORE Article 10 February 2025 UP-TO-FIVEFOLD REVERBERATING WAVES THROUGH THE EARTH’S CENTER AND DISTINCTLY ANISOTROPIC INNERMOST
INNER CORE Article Open access 21 February 2023 TILTED TRANSVERSE ISOTROPY IN EARTH’S INNER CORE Article 27 September 2024 REFERENCES * Yoshida, S., Sumita, I. & Kumazawa, M. Growth
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Google Scholar Download references ACKNOWLEDGEMENTS We are grateful to the IRIS, J-array Data Center, W. Shannon and L. Saumure for supplying the data. We thank S. Tanaka for providing us
their PKP-PKIKP data. We also thank H. Kawakatsu, S. Sacks and P. Silver for comments on the manuscript. Discussions with J. Aurnou, M. Fouch, W. Holt, S. Solomon, I. Sumita, S. Tanaka and
D. Weidner were helpful in preparing the manuscript. This work is supported by the fellowship of the Carnegie Institution of Washington and an NSF grant. AUTHOR INFORMATION AUTHORS AND
AFFILIATIONS * Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road NW, Washington, 20015, DC, USA Fenglin Niu * Department of Geosciences, State
University of New York at Stony Brook, Stony Brook, 11794, New York, USA Lianxing Wen Authors * Fenglin Niu View author publications You can also search for this author inPubMed Google
Scholar * Lianxing Wen View author publications You can also search for this author inPubMed Google Scholar CORRESPONDING AUTHOR Correspondence to Fenglin Niu. RIGHTS AND PERMISSIONS
Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Niu, F., Wen, L. Hemispherical variations in seismic velocity at the top of the Earth's inner core. _Nature_ 410, 1081–1084
(2001). https://doi.org/10.1038/35074073 Download citation * Received: 18 July 2000 * Accepted: 28 February 2001 * Issue Date: 26 April 2001 * DOI: https://doi.org/10.1038/35074073 SHARE
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