Abstract

Using a large collection of free-oscillation data and additional constraints imposed by the free-air gravity anomaly, lateral variations in shear velocity, compressional velocity, and density within the mantle, dynamic topography on the free surface, and topography on the 660-km discontinuity and the core-mantle boundary are determined. The velocity models are consistent with existing models based upon travel-time and waveform inversions. In the lowermost mantle, near the core-mantle boundary, denser than average material is found beneath regions of upwellings centered on the Pacific Ocean and Africa characterized by slow shear velocities. These anomalies suggest the existence of compositional heterogeneity near the core-mantle boundary.

Normal-Mode Constrained Mantle Models

Reference

Ishii, M., and Tromp, J., 1999.
Normal-mode and free-air gravity constraints on lateral variations in velocity and density of Earth's mantle. Science 285, 1231-1236.

Ishii, M., and Tromp, J., 2001.
Even-degree lateral variations in the Earth's mantle constrained by free oscillations and the free-air gravity anomaly. Geophys. J. Int., 145, 77-96.

Normal Mode Page

Miaki Ishii, Department of Earth and Planetary Sciences, Harvard University.
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Last modified: April 17, 2001.