Continent-ocean chemical heterogeneity in the mantle based on seismic tomography.

Seismic models of global-scale lateral heterogeneity in the mantle show systematic differences below continents and oceans that are too large to be purely thermal in origin. An inversion of the geoid, based on a seismic model that includes viscous flow in the mantle, indicates that the differences beneath continents and oceans can be accounted for by differences in composition in the upper mantle superposed on mantle-wide thermal heterogeneities. The net continent-ocean density differences, integrated over depth, are small and cause only a low flux of mass and heat across the asthenosphere and mantle transition zone.

Global Images of the Earth's Interior.

The three-dimensional maps of the earth's interior now span regions from the bottom of the crust to the inner core of the earth. Although a wealth of new information on the dynamics of the earth has been discovered, the inner core offers the greatest surprise: it appears to be anisotropic with the axis of symmetry aligned with the axis of rotation.

Overtones of Free Oscillations and the Structure of the Earth's Interior.

Identification of 82 percent of all possible spheroidal overtones with greater than 300 seconds increases the resolving power of the set of gross searth data. Results of inversion indicate a change of composition in the deepest 500 kilometers of the mantle. The assumption that the inner core is rigid is required to satisfy simultaneously the data on free oscillations and travel times.