Published in the at-meeting AGU 1991 Fall Meeting Program (p.177) as an Additional Abstract, presented as Poster T32C-12
Degree One Components in the Earth's Interior
In the past, analysis of global geophysical functions has emphasized correlations with the nonhydrostatic geoid, but a correlation between the geoid and any other function is undefined at degree one. Degree one components are zero for appropriate choice of reference frame, by definition. Once the frame is fixed for the Earth's geoid, however, other functions (e.g., interior density, hotspot distribution, residual geoid, chemical boundary, bathymetry and topography) have degree one components that indicate nonhydrostatic conditions which have to be explained geophysically. Their significance has seldom been analyzed.
I have found high correlations (r > 0.98) at degree one between the hotspot distribution, the slab residual geoid, and lower mantle equivalent geoid. The statistical significance is diminished somewhat, since there is only one degree of freedom. The interpretation of degree one functions derived from seismic tomography is uncertain because of possible effects of station and source corrections, and station distribution. One possible way around this is to study the mantle geoid, as evidenced by ridge height, and thus remove the lower density water layer.