The response functions can then be convolved with a distribution of internal density anomalies to calculate the geoid.
Seismology provides a model of the internal structure of the mantle.
Shear waves, or S -waves, are internal body waves whose motion is perpendicular to the direction of propagation of the wave. This 3-D image of structure is refered to as a tomographic model. All of the mantle viscosity studies that use a density anomaly model to drive flow in the mantle, use these tomographic models, or a density model based on past history of plate tectonics. This includes all mantle viscosity models based on geoid an plate velocities. One way in which some of the assumptions about seismic models can be tested is to develop a tomogram of density anomalies based on the location of subducted slab material from plate reconstruction histories.