Robust normal mode constraints on inner-core anisotropy from model space search.
A technique for searching full model space that was applied to measurements of anomalously split normal modes showed a robust pattern of P-wave and S-wave anisotropy in the inner core. The parameter describing P-wave anisotropy changes sign around a radius of 400 kilometers, whereas S-wave anisotropy is small in the upper two-thirds of the inner core and becomes negative at greater depths. Our results agree with observed travel-time anomalies of rays traveling at epicentral distances varying from 150 degrees to 180 degrees. The models may be explained by progressively tilted hexagonal close-packed iron in the upper half of the inner core and could suggest a different iron phase in the center.
Beghein
Caroline
C
Faculty of Earth Sciences, Utrecht University, Post Office Box 80021, 3508 TA Utrecht, Netherlands. beghein@geo.uu.nl
Trampert
Jeannot
J