Abstract
Elastic thickness (Te) is a parameter representing the lithospheric strength with respect to the loading. Those places, having large values of elastic thickness, flexes less. In this paper, the on-orbit measured gravitational gradients of the Gravity field and steady-state Ocean Circulation Explorer (GOCE) mission are used 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 derivative of the Earth’s gravity field measured by the GOCE satellite and mechanical properties of the lithosphere. The loading of topography and bathymetry, sediments and crystalline masses are computed 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 radial 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 on-orbit gradient. This method is developed in terms of spherical harmonics and performed at any point along the GOCE orbit without using any planar approximation. Our map of Te over Africa shows that the intra-continental hotspots and volcanoes, such as Ahaggar, Tibesti, Darfur, Cameroon volcanic line and Libya are connected by corridors of low Te. The high values of Te are mainly associated with the cratonic areas of Congo, Chad and the Western African basin.
Highlights
The Gravity field and steady-state Ocean Circulation Explorer (GOCE, Drinkwater et al 2003) was the first satellite mission, which measured the secondorder directional derivatives of the gravitationalAccording to Airy’s (1855) theory of isostasy, the mountains have roots beneath
The effect of the long wavelength portion of the gradiometric data, which comes mainly from the deep mantle is reduced from the GOCE data and Te will be estimated based on our forward computational method over Africa
We have developed a forward computation method based on a combination of Vening MeineszMoritz and flexural theories of isostasy for Te modelling from the on-orbit GOCE data
Summary
The Gravity field and steady-state Ocean Circulation Explorer (GOCE, Drinkwater et al 2003) was the first satellite mission, which measured the secondorder directional derivatives of the gravitational. The original idea of Vening Meinesz (1931) was based on loading theory In this way, the mechanical properties of the lithosphere, like rigidity, elastic thickness (Te), Young’s modulus and Poisson’s ratio are considered instead of gravity data. Vening Meinesz (1931) assumed that the lithosphere is an elastic shell with the thickness Te, which can be determined according to the coherence methods (Forsyth 1985) comparing gravity data to topographic heights. The effect of the long wavelength portion of the gradiometric data, which comes mainly from the deep mantle is reduced from the GOCE data and Te will be estimated based on our forward computational method over Africa We chose this area because only one study was dealing with Te determination over the whole African continent. The main purpose of this paper is to present a method for Te modelling from the GOCE on-orbit data rather than a geophysical interpretation
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