Compressibility of the Earth.
Although we use to think that the rocks are incompressible, a batch of mantle that flows from the uppermost
mantle to the core-mantle boundary almost doubles in density!
In the figure below I plotted the density profile inside the Earth mantle (based on PREM). Most of the
density increase in the upper mantle is due to the solid-solid phase
transformations. In the lower mantle (below 670-km depth), however, densification occurs mainly due to the
high pressure of what lies above.
Of course, depending on the density structure, the gravitational acceleration
(and therefore the gravitational
pull/push acting on the density anomaly inside the mantle) would be different.
In the right-right figure you could see by how much does the g(r) change.
The solid lines correspond to
PREM-density and PREM-gravity. The dashed lines correspond to the constant-density mantle.
I begun to investigate Earth compressibility in my graduate school.
My thesis advisor Bradford Hager
and a collaborator Alessandro Forte
took an active and willing participation in the study.
We investigated the effects of Earth compressibility on the geoid and published
results in the paper.