Internal loading of a compressible earth: Effect of a solid lithosphere

This paper shows the importance of including a lithosphere in the Earth model when inferring a mantle viscosity profile or density-velocity conversion factor from mantle circulation. The free-slip and no-slip conditions are investigated at the mantle-lithosphere boundary. Results obtained for Earth models that include a lithosphere are compared with those obtained for models where no lithosphere is considered. In particular, it is shown that models without a lithosphere are inconsistent with the no-slip condition at the mantle-lithosphere interface, because they introduce a tangential stress discontinuity at that level. With regard to the estimations of the mantle viscosity profile from the comparison between observed and computed geoids and plate velocities, the principal results obtained previously using the no-slip condition without a lithosphere (i.e. the best fit is obtained for a one-cell convection with a large viscosity jump at a depth of 670 km) are still valid. Nevertheless, to infer a precise viscosity profile or density-velocity conversion factor when using the no-slip condition, a lithosphere must be accounted for, because the results are different for models with and without a lithosphere. (C) 1997 Published by Elsevier Science B.V.