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Published online on October 8, 2002, 10.1073/pnas.172508499
PNAS | October 29, 2002 | vol. 99 | no. 22 | 14026-14030


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From the Cover
Geophysics
The innermost inner core of the earth: Evidence for a change in anisotropic behavior at the radius of about 300 km

Miaki Ishii *, and Adam M. Dziewoski

Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138

Contributed by Adam M. Dziewonski and approved August 22, 2002

Since the discovery of the inner core in 1936, no additional spherical subshell of the Earth has been observed. Based on an extensive seismic data set, we propose the existence of an innermost inner core, with a radius of ~300 km, that exhibits a distinct transverse isotropy relative to the bulk inner core. Specifically, within the innermost inner core, the slowest direction of wave propagation is ~45° from the east-west direction. In contrast, the direction of the slowest wave propagation in the overlying inner core is east-west. The distinct anisotropy at the center of the Earth may represent fossil evidence of a unique early history of inner-core evolution.

Abbreviations: IMIC, innermost inner core

* To whom correspondence should be addressed. E-mail: ishii{at}seismology.harvard.edu.

See commentary on page 13966.


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Related Commentary in PNAS:

The inner inner core of Earth
Don L. Anderson
PNAS 2002 99: 13966-13968. [Extract] [Full Text]  



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