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Estimation of Litospheric Elastic Thicknes from In-orbitGOCE-based Vertical Gradients and CRUST1.0
Pitoňák, Martin ; Eshagh, Mehdi ; Šprlák, Michal ; Novák, Pavel
The lithospheric strength with respect to the loading is represented by a parameter called elastic thickness (Te) and places with larger value of Te flex less. In this contribution, we use the in-orbit vertical gravitational gradients measured by Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite for determining the elastic thickness over Africa. A forward computational method is developed based on the Vening Meinesz-Moritz (VMM) and flexural theories of isostasy to find a mathematical relation between the second-order vertical derivative of the gravitational potential and mechanical properties of the lithosphere. This method is developed in terms of spherical harmonics. Loading effects of topography and bathymetry, sediments and crystalline masses are calculated from CRUST1.0, in addition to estimates of laterally-variable density of the upper mantle, Young’s modulus and Poisson’s ratio. The second-order vertical derivatives of the gravitational potential are synthesised from the crustal model and different a priori values of elastic thickness to find which one matches the GOCE in-orbit vertical gradient. Our map of Te over Africa shows that the high values of Te are mainly associated with the cratonic areas of Congo, Chad and the Western African basin while the intra-continental hotspots and volcanoes, such as Ahaggar, Tibesti, Darfur, Cameroon volcanic line and Libya are connected by corridors of low Te.
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