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Robust Normal Mode Constraints on Inner-Core Anisotropy from Model Space Search
Caroline Beghein,*Jeannot Trampert
A technique for searching full model space that was applied to
measurements of anomalously split normal modes showed a robustpattern
of P-wave and S-wave anisotropy in the inner
core. Theparameter describing P-wave anisotropy changes
sign around a radiusof 400 kilometers, whereas S-wave
anisotropy is small in the uppertwo-thirds of the inner core and
becomes negative at greater depths.Our results agree with observed
travel-time anomalies of raystraveling at epicentral distances varying
from 150° to 180°. Themodels may be explained by progressively
tilted hexagonal close-packediron in the upper half of the inner core
and could suggest a differentiron phase in the center.
Faculty of Earth Sciences, Utrecht University, Post Office Box
80021, 3508 TA Utrecht, Netherlands.
*
To whom correspondence should be addressed. E-mail:
beghein{at}geo.uu.nl
