Estimates of Te from GOCE data

The cold upper part of the lithosphere can support the elastic stresses that govern rigid plate movements and support the Earth's topography. In many regions the thickness Te of the layer involved can be estimated from the relationship between surface gravity measurements and topography. However, there are extensive regions of the continents where the topography is well determined, but the gravity field is not. The obvious solution to this problem is to use the satellite, rather than the surface, gravity field. The wavelength range of interest, 200–500 km, requires a satellite with a low orbit. The first satellite to satisfy this requirement is the Gravity field and steady state OCean Explorer (GOCE). Measurements of the elements of the gravity gradient tensor and determinations of the spherical harmonic coefficients of the gravity field based on GOCE observations are used to estimate Te. For Hawaii these estimates are 18.4 km and 21.4 km respectively, and agree well with a value of 18.2 km obtained from the surface gravity field determined from altimetry. An attempt to estimate the value of Te of the central North Atlantic using GOCE data was not successful, whereas surface data gives a value of about 4 km. Estimates for Tibet and surrounding regions, where the gravity field from surface measurements is poorly determined, are 25–32 km. The NW part of S. America gives 17–24 km. The difference in the values of Te from the two regions probably results from the difference in lithospheric thicknesses. Estimates of Te from central and southern Africa, of 31–34 km, are less well constrained than are those from Tibet and S. America. These results show that the data from GOCE can be used to estimate the value of Te where it is poorly determined from surface measurements, is greater than ∼15 km, and where large topographic loads produce large gravity anomalies.