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Investigation of time dependent inner core structure by the analysis of free oscillation spectra
Earth, Planets and Space volume 50, pages1013–1018(1998)
Proposals that the seismic structure of the Earth’s inner core is time-dependent are investigated using the splitting functions of free oscillations, determined from seismic data recorded over some 20 years. It is shown that the data support some time-dependence, although the paucity of the data for the 1970’s and 1980’s makes it difficult to be certain of the precise form of such time dependence. The data do not support a positive (i.e. West-to-East) rotation; rather, the inferred rotational component of the time-dependent inner core structure is negative (i.e. East-to-West), and varies according to the mode under consideration from less than 1° per year to more than 2° per year. The analysis suggests that inner core structure is time-dependent but that the dependence is not well explained by differential rotation of the inner core. This kind of analysis will become much more powerful with increasing quantities of data over a longer time span.
Abramowitz, M. and I. A. Stegun, Handbook of Mathematical Functions, Dover Publications, New York, 1965.
Creager, K. C., Inner core rotation rate from small-scale heterogeneity and time-varying travel times, Science, 278, 1284–1288, 1997.
Giardini, D., X.-D. Li, and J. H. Woodhouse, Three-dimensional structure of the Earth from splitting in free oscillation spectra, Nature, 325, 405–411, 1987.
Giardini, D., X.-D. Li, and J. H. Woodhouse, Splitting functions of long-period normal modes of the Earth, J. Geophys. Res., 93(B11), 13716–13742, 1988.
Glatzmaier, G. A. and P. H. Roberts, A three-dimensional self-consistant computer simulation of a geomagnetic field reversal, Nature, 377, 203–209, 1995.
Kuang, W. and J. Bloxham, An Earth-like numerical dynamo model, Nature, 389, 371–374, 1997.
Morelli, A., A. M. Dziewonski, and J. H. Woodhouse, Anisotropy of the inner core inferred from PKIKP travel times, Geophys. Res. Lett., 13, 1545–1548, 1986.
Ritzwoller, M., G. Masters, and F. Gilbert, Observations of anomalous splitting and their interpretation in terms of aspherical structure, J. Geophys. Res., 91, 10203–10228, 1986.
Song, X., Anisotropy of the Earth’s inner core, Rev. Geophys., 35(3), 297–313, 1997.
Song, X.-D. and P. Richards, Seismological evidence for differential rotation of the Earth’s inner-core, Nature, 382(6588), 221–224, 1996.
Souriau, A., P. Roudil, and B. Moynot, Inner core differential rotation: Facts and artifacts, Geophys. Res. Lett., 24(16), 2103–2106, 1997.
Stevenson, D. J., Limits on lateral density and velocity variations in the Earth’s outer core, Geophys. J. Roy. Astron. Soc., 88, 311–319, 1987.
Su, W.-J. and A. M. Dziewonski, Inner-core anisotropy in 3 dimensions, J. Geophys. Res., 100(B6), 9831–9852, 1995.
Su, W.-J., R. L. Woodward, and A. M. Dziewonski, Degree 12 model of shear velocity heterogeneity in the mantle, J. Geophys. Res., 99(B4), 6945–6980, 1994.
Su, W.-J., A. M. Dziewonski, and R. Jeanloz, Planet within a planet: Rotation of the inner core of the Earth, Science, 274, 1883–1887, 1996.
Woodhouse, J. H. and D. Giardini, Inversion for the splitting function of isolated low order normal mode multiplets, EOS Trans. AGU, 66, 300, 1985.
Woodhouse, J. H., D. Giardini, and X. D. Li, Evidence for inner core anisotropy from free oscillations, Geophys. Res. Lett., 13, 1549–1552, 1986.
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Sharrock, D.S., Woodhouse, J.H. Investigation of time dependent inner core structure by the analysis of free oscillation spectra. Earth Planet Sp 50, 1013–1018 (1998) doi:10.1186/BF03352195
- Rotation Rate
- Core Structure
- Inner Core
- Differential Rotation
- Core Mode