Deviation of the Earth’s crust and upper mantle from isostatic equilibrium

Gravity anomalies in the Earth's crust and upper mantle

“…They are calculated in quadratic approximation. For this calculus we used the expansion of degree N = 36 of relief heights, of depths M and of anomalous masses of crust and mantle, obtained in our previous works [1,2]. The quadratic terms contribution is most significant in regions where M boundary is situated in depth and reaches 40 mGal in Tibet region.…”

“…It illustrates the absence of isostatic compensation of relief on M, and existence of density and stress anomalies in the crust and the upper mantle of the Earth. The knowledge of direct and inverse regression functions has allowed the separation of equation for total equilibrium of the crust and the upper mantle in two components: (1) partial compensation of crust pressure on surface M; (2) pressure compensation on some depth in the mantle for the parts of the crust, not compensated on M, (similar equations for Archimedean equilibrium). * Solution of equilibrium equations for the 5 • × 5 • cells of the whole Earth allowed to determine the optimum depths of compensation, with minimized functional, depending on density and stress anomalies in the crust and the upper mantle.…”

“…* Solution of equilibrium equations for the 5 • × 5 • cells of the whole Earth allowed to determine the optimum depths of compensation, with minimized functional, depending on density and stress anomalies in the crust and the upper mantle. The comparative analysis of conditions of the crust isostatic equilibrium for various variants of compensation for each cell allows to construct the maps of optimum (in sense of potential energy minimum) distribution of anomalous masses and stresses in the crust and the upper mantle (reaching ±7 × 106 kg/m 2 and ±15 MPa) [2].…”