Conclusions

Abstract

The topmost and lowermost few hundred kilometres of the mantle are where the sharpest contrast in material properties occur in the Earth. For this reason, these are the sites of strongest gradients in temperature, forming boundary layers, and are where direct evidence for the movement of the mantle are to be found. Seismic anisotropy has proved to be invaluable in measuring flow in the uppermost mantle, and appears to be the key to understanding the same near the core-mantle boundary. In this thesis I have reviewed previous attempts to understand how and if we can infer flow from measurements of seismic anisotropy, finding that especially for the lowermost mantle, there are still several possibilities to be explored. I present new data which show that some previous assumptions about the style of anisotropy present in the deep Earth need to be revised, and develop models of D” anisotropy which suggest that we are still some way from being able to confidently claim that the cause of seismic anisotropy there is always the alignment of mineral grains.