2015 Evidence for equatorial anisotropy of Earth’s inner-inner core

Original paper: Wang, T., X.D. Song, Xia H. Han, Equatorial anisotropy of Earth’s inner inner core from autocorrelation of earthquake coda, Nature Geosci., 8 (3), 224-227, doi:10.1038/ngeo2354, 2015.

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BBC News – Heart of Earth’s inner core revealed
Earth’s Inner Core Found To Have A Core Of Its Own
The surprising heart of the Earth’s core has been revealed, scientists say – The Washington Post
Solid inner, inner core may be relic of Earth’s earliest days | Science News
地核内核内内核:科学家发现地球核心的新结构 | 科学人 | 果壳网 科技有意思
Video: Researchers discover the Earth’s inner-inner core – NSF ScienceNow
Video: Earth’s inner core has a core of its own, scientists discover | Toronto Star
Video: BBC Children newsround


2009 Evidence for temporal changes of the Earth’s media associated with great Sumatra earthquakes

Original paper: Xu, Z.J., and X.D. Song, Temporal changes of surface wave velocity associated with major Sumatra earthquakes from ambient noise correlation, Proc. Natl. Aca. Sci. USA, 106, 14207-14212, 2009.

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2008 Confirmation of the Earth’s innermost inner core

Original papers:
Sun, X.L., and X.D. Song, The inner inner core of the Earth: Texturing of iron crystals from three-dimensional seismic anisotropy, Earth Planet. Sci. Lett., 56-65, doi:10.1016/j.epsl.2008.01.049, 2008. 
Sun, X.L., and X.D. Song, Tomographic inversion for three-dimensional anisotropy of Earth’s inner core, Phys. Earth. Planet. Inter., 167, 53-70, doi:10.1016/j.pepi.2008.02.011, 2008.

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2005 Confirmation of the inner core super-rotation

Original paper: Zhang, J., X.D. Song, Y.C. Li, P.G. Richards, X.L. Sun, F. Waldhauser, Inner core differential motion confirmed by earthquake doublet waveform doublets, Science, 309, 1357-1360, doi:10.1126/science.1113193, 2005.

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1998 Evidence for a layered inner core structure

Original paper: Song, X.D., and D.V. Helmberger, Seismological evidence for an inner core transition zone, Science, 282, 924-927, 1998.

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1996 Evidence for the super-rotation of the Earth’s inner core

Original paper: Song, X.D., and P.G. Richards Seismological evidence for differential rotation of the Earth’s inner core, Nature, 382, 221-224, 1996.

Columbia University Archive