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Science 13 December 1996:
Vol. 274. no. 5294, pp. 1883 - 1887
DOI: 10.1126/science.274.5294.1883
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Reports

Planet Within a Planet: Rotation of the Inner Core of Earth

Wei-jia Su, Adam M. Dziewonski, * Raymond Jeanloz

The time dependence of the orientation of Earth's inner core relative to the mantle was determined using a recently discovered 10-degree tilt in the axis of symmetry of the inner core's seismic-velocity anisotropy. Two methods of analyzing travel-time variations for rays traversing the inner core, on the basis of 29 years of data from the International Seismological Centre (1964-1992), reveal that the inner core appears to rotate about 3 degrees per year faster than the mantle. An anomalous variation in inner-core orientation from 1969 to 1973 coincides in time with a sudden change ("jerk") in the geomagnetic field.

W.-J. Su and A. M. Dziewonski, Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA.
R. Jeanloz, Department of Geology and Geophysics, University of California, Berkeley, CA 94720-4767, USA.
*   To whom correspondence should be addressed.

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