HR: 17:24h
AN: T54A-07    [Abstracts]
TI: Inner Core Anisotropy as Seen With Normal Mode Data and the Neighbourhood Algorithm
AU: Trampert, J
EM: jeannot@geo.uu.nl
AF: Utrecht University, 4 Budapestlaan P.O. Box 80.021, Utrecht, 3508 TA Netherlands
AU: * Beghein, C
EM: beghein@mit.edu
AF: MIT, 77 Massachusetts avenue room 54-526, cambridge, MA 02139 United States
AB: A model space search technique applied to core-sensitive normal mode splitting measurements reveals a robust pattern of P-wave and S-wave anisotropy in the inner core. In the classical inverse approach, regularization and normal mode data quality have a significant influence on the final model, whereas the chosen mantle model was less crucial. This is the most likely explanation for discrepancies among existing seismological models of inner core anisotropy. We employed a forward modelling approach, the neighbourhood algorithm, to obtain all possible models of inner core anisotropy compatible with carefully chosen free oscillation data. Our models reveal a relatively complex radial dependence of the anisotropy, with a likely change of sign in the parameters in the deepest part of the inner core. The parameter describing P-wave anisotropy changes sign around 800~km depth, while S-wave anisotropy is small in the upper two-thirds of the inner core and becomes negative at greater depths. Our results are in agreement with all observed travel-time anomalies of rays travelling through the inner core and are the first models derived from normal mode data alone that have significant anisotropy in the deepest part of the inner core. They predict between four and six seconds of travel-time anomalies for rays travelling at epicentral distances of $170^\circ$. Possible interpretations of these models include a phase change of iron in the centre of the core.
DE: 7260 Theory and modeling
DE: 7207 Core and mantle
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting