Odhad hrúbky litosféry z vertikálnych gradientov meraných družicou GOCE a modelu CRUST 1.0
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2022-02-03
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Vysoké učení technické v Brně,Fakulta stavební
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Elastická hrúbka litosféry (Te) je parameter predstavujúci litosférickú pevnosť vzhľadom na zaťaženie. Tieto miesta s veľkými hodnotami elastickej hrúbky sa ohýbajú menej. V tomto príspevku sa na určenie hrúbky litosféry v Afrike používajú gravitačné gradienty merané družicou GOCE. Výpočtová metóda bola odvodená na základe teórie podľa Vening Meinesz-Moritz (VMM) a teórie ohybu izostázy na nájdenie matematického vzťahu medzi druhými deriváciami tiažového potenciálu meraného družicou GOCE a mechanickými vlastnosťami litosféry a je založená na priamom modelovaní. Topografia a batymetria bola modelovaná pomocou modelu DTM2006.0. Efekty zaťaženia sedimentov a kryštalických hmôt boli odhadnuté z modelu CRUST1.0. Z rovnakého modelu boli odhadnuté laterálne zmeny hustoty horného plášťa, hodnoty Youngovho modulu a Poissonovho pomeru. Druhé derivácie gravitačného potenciálu boli generované z modelu kôry a rôznej hodnoty elastickej hrúbky litosféry, aby sa zistilo, ktorý z nich zodpovedá gradientu GOCE na obežnej dráhe. Táto metóda bola odvodená v tvare sférických harmonických funkcií a použiteľná v akomkoľvek bode pozdĺž orbity GOCE bez použitia akejkoľvek rovinnej aproximácie. Naše hodnoty Te nad Afrikou ukazujú, že vnútrozemské hotspoty a sopky, ako sú Ahaggar, Tibesti, Darfúr, sopečná linka Kamerun a Líbya, sú spojené koridormi nízkeho Te. Vysoké hodnoty Te sú prevažne spojené s kronickými oblasťami Konga, Čadu a západnej Afriky.
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.
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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Družicové metody v geodézii a katastru 2022, s. 63-64. ISBN 978-80-86433-77-6.
http://geodesy.fce.vutbr.cz/konference/gnss-seminar/
http://geodesy.fce.vutbr.cz/konference/gnss-seminar/
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