Earth Structure from Free Oscillations and Travel Times

Abstract

An extensive set of reliable gross Earth data has been inverted to obtain a new estimate of the radial variations of seismic velocities and density in the Earth. The basic data set includes the observed mass and moment of inertia, the averaged periods of free oscillation, and five new sets of differential travel-time data. The eigenperiod data was drawn mainly from the Dziewonski-Gilbert study. The differential travel-time data consists of the times of PcP-P, ScS-S, P_(AB)'-P_(DF)' and P_(BC)'-P_(DF)'. These data were inverted using the linear estimation algorithm described by Jordan (PhD Thesis, California Institute of Technology, 1972). A simple but realistic starting model was constructed based on a number of physical assumptions, such as requiring the Adams-Williamson relation to hold in the lower mantle and core. By using baselifie-insensitive differential travel times and averaged eigenperiods, a considerable improvement in both the quality of the fit and the resolving power has been realized. The spheroidal and torodial data are fit on the average to 0.04 and 0.08 per cent, respectively. The final model, designated model B1, also agrees with Rayleigh and Love wave phase and group velocity data.