HR: 17:36h
AN: T54A-08    [Abstracts]
TI: Constraints on inner core structure from normal mode coupling
AU: Andrews, J
EM: andrews@esc.cam.ac.uk
AF: University of Cambridge, Madingley Road, Cambridge, CB3 0EZ United Kingdom
AU: * Deuss, A
EM: deuss@esc.cam.ac.uk
AF: University of Cambridge, Madingley Road, Cambridge, CB3 0EZ United Kingdom
AU: Woodhouse, J H
EM: john.woodhouse@earth.ox.ac.uk
AF: University of Oxford, Parks Road, Oxford, )X1 3PR United Kingdom
AB: Since early last century it has been known that the Earth has an inner core and normal mode observations provided first seismological evidence for its solidity in the early 1970's. During the last two decades, observations of anomalous splitting of core sensitive modes has been interpreted in terms of a significant amount of anisotropy in the inner core. Thus, normal mode data, in addition to body wave data, place important comstraints on inner core structure and have been used to make fundamental discoveries of different types of inner core structure. We study the anisotropic, attenuation and shear wave structure of the inner core using normal mode data. Inner core structure has traditionally been studied using splitting of isolated modes. Here we extend this method to include cross-coupling between core sensitive modes that are closely spaced in frequency. We find that several inner core modes are strongly coupled due to degree two structure, in particular mantle shear wave velocity and inner core anisotropy. This provides new constraints on models of inner core anisotropy and implies that we cannot ignore cross-coupling for core sensitive modes. Certain closely spaced pairs of core modes are also very sentive to small changes in inner core shear wave velocity. A small change in inner core shear wave velocity, within the permissable bounds of normal mode data and the observation of PKJKP, makes certain modes visible that were previously identified as `high Q modes', for example $_{10}S_2$ and $_{11}S_2$. Thus, there is no need for a very high Q in the inner core as has been suggested in several previous studies and review papers.
DE: 7255 Surface waves and free oscillations
DE: 7299 General or miscellaneous
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 8155 Plate motions--general
DE: 7207 Core and mantle
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting