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!

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.