Density Modelling by Monte Carlo Inversion--II Comparison of Recent Earth Models

Density models for the Earth have been proposed by Haddon & Bullen, Press, and Wang which satisfy similar data to similar confidence limits and yet differ markedly in the region of the upper mantle. An analysis of the effects of various constraints by Monte Carlo inversion techniques shows that these differences are due predominantly to differences in assumptions about the permissible range of values for upper mantle shear velocity. A final solution of the problem depends on better knowledge of upper mantle shear velocities in oceanic regions. However, some improvement could result from a reassessment of the non-uniqueness bounds of the presently available data.