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Inversion conjointe des données magnétotelluriques et gravimétriques: Application à l'imagerie géophysique crustale et mantellique

Abstract : Understanding geology from geophysical investigation is best when information is obtained from different kinds of data. A single method may not have sufficient resolution to provide the expected information. Joint inversion is a step forward to quantitatively combine data of different nature. Joint inversion may be considered in two different ways, petrophysical or structural. We may subdivide a joint inversion into two categories, joint inversion of data function of the same physical parameter, such as DC-DC or AC-DC resistivity soundings, and joint inversion of data of different nature such as gravity and seismic or seismic and magnetotelluric (MT) .Here, I present a solution for the joint inversion between MT and gravity data. The depth resolution but poor spatial coverage of MT data may be complementary of gravity data with excellent spatial coverage but little vertical resolution.With data of different nature, the most important problem in the joint inversion is to define how to link both parameters. Analytical formulation between for instance seismic velocity and density or electrical resistivity and density are seldom and very specific. It is in general not obvious to link them through petrophysical relationships.As a consequence, it is necessary to develop algorithms that are free of any explicit formulation between the parameters. The inversion scheme presented here is quite general. I set a Geometrical Condition Function (GCF) under which parameters must vary in similar domains to image the same underground layers.The method presented here was tested and validated on synthetic examples. Joint inversion were realized on field data which were acquired in Turkana area, northern Kenyan, branch of East African Rift System. The results obtained confirmed reflection seismic results obtained in the same area, and brought new information about the subsurface structure. This study allowed to define two Basins (half-graben basin) and determine the thickness of Turkana Volcanics, which unknown until now . A stratigraphic sequence is proposed for both Turkana and Kachoda basins. The results of lithospheric study showed a heterogeneous crust and homogeneous upper mantle. Two anomalies are localized on the lower crust. They are interpreted as partial fusion area without upper mantle connection.
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Submitted on : Thursday, October 15, 2009 - 3:57:43 PM
Last modification on : Friday, April 5, 2019 - 8:16:47 PM
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  • HAL Id : tel-00424413, version 1

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Yassine Abdelfettah. Inversion conjointe des données magnétotelluriques et gravimétriques: Application à l'imagerie géophysique crustale et mantellique. Sciences de la Terre. Université de Bretagne occidentale - Brest, 2009. Français. ⟨tel-00424413⟩

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