The importance of GRM gravity observations in continental regions
Altimetric satellites showed the existence of gravity anomalies with wavelengths between 1500 km and 3000 km which correlated with residual depth anomalies. It was suggested that there is also an even smaller scale convective circulation with a wavelength of less than 500 km. Numerical experiments and SEASAT profiles demonstrate that similar small scale circulation must also exist near fracture zones. The mantle therefore must contain at least three scales of circulation: (1) comparable to the plate dimensions, the large scale circulation, which returns material from the Island arcs to the ridges; (2) an intermediate scale comparable to the depth of the upper mantle; and (3) a small scale comparable to the thickness of the asthenosphere. This picture was established by observations of gravity and bathymetry in oceanic regions.