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Depth dependence of anisotropy of Earth's inner core

Song, Xiaodong and Helmberger, Don V. (1995) Depth dependence of anisotropy of Earth's inner core. Journal of Geophysical Research B, 100 (B6). pp. 9805-9816. ISSN 0148-0227. doi:10.1029/95JB00244.

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Both body wave (PKP) travel times (Creager, 1992; Song and Helmberger, 1993a; McSweeney and Creager, 1993; Shearer, 1994) and fits to the splitting of core modes (Tromp, 1993) show general agreement that the top 300 km of inner core is very anisotropic. The anisotropy displays axial symmetry around the Earth's spin axis, with the polar direction 3% faster than the equatorial direction. One key problem now is the depth dependence of the inner core anisotropy. Here we extend our polar path studies to include both long-period and short-period modeling for the PKP phases at ranges 120° to 173°. Arrivals from the top of the inner core (PKIKP) and reflections from the inner core boundary (PKiKP) can be observed distinctly in short-period records at ranges 130° to 140° and as waveform distortions in the long-period records at ranges 130° to 146°. These waveforms provide a new set of data for examining the topmost 150 km of the inner core, which is not well sampled by the previous body wave travel times. Record sections of waves traversing the inner core nearly parallel to the Earth's spin axis (polar paths) from three events, two beneath the South Sandwich Islands and one along the Macquarie Ridge, recorded at World Wide Standardized Seismograph Network, Canadian Network, and Long Range Seismic Measurements stations are analyzed. Our results suggest that the top 150 km of the inner core is only weakly anisotropic (less than 1%), with strong evidence indicating that the top 60 km is not anisotropic at all.

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Additional Information:© 1995 American Geophysical Union. Received July 8, 1994; revised December 31, 1994; accepted January 19, 1995. We thank Peter Shearer for the preprint before publication and Jeroen Tromp from constructive discussions. We also thank Eddie Ganero and Don Anderson for helpful reviews. The reviews from Peter Shearer, George Helffrich, and Craig Bina. greatly improved the manuscript. This research was supported by the National Science Foundation grant EAR-93-16441. Division of Geological and Planetary Sciences, California. Institute of Technology, contribution 5426.
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Caltech Division of Geological and Planetary Sciences5426
Issue or Number:B6
Record Number:CaltechAUTHORS:20121128-094644476
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Official Citation:Song, X. and D. V. Helmberger (1995), Depth dependence of anisotropy of Earth's inner core, J. Geophys. Res., 100(B6), 9805–9816, doi:10.1029/95JB00244.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:35694
Deposited By: Ruth Sustaita
Deposited On:28 Nov 2012 17:57
Last Modified:09 Nov 2021 23:17

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