Modelling and analysis of electromagnetic fields in 3D inhomogeneous media

Červ, Václav; Pek, Josef

doi:10.1007/bf01901660

Cited by 19 publications

(5 citation statements)

References 67 publications

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“…However, most EM software developers refrain from implementation of the IE approach, since accurate computation of the matrix A IE is indeed an extremely tedious and nontrivial problem itself. Yet this approach has been implemented in several studies (Ting and Hohmann, 1981;Wannamaker et al, 1984;Newman and Hohmann, 1988;Hohmann, 1988;Cerv, 1990;Wannamaker, 1991;Dmitriev and Nesmeyanova, 1992;Xiong, 1992;Xiong and Tripp, 1995;Kaufman and Eaton, 2001, among others).…”

Section: Integral Equation Approachmentioning

confidence: 96%

Three-Dimensional Electromagnetic Modelling and Inversion from Theory to Application

Avdeev

2005

Surv Geophys

246

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The whole subject of three-dimensional (3-D) electromagnetic (EM) modelling and inversion has experienced a tremendous progress in the last decade. Accordingly there is an increased need for reviewing the recent, and not so recent, achievements in the field. In the first part of this review paper I consider the finite-difference, finite-element and integral equation approaches that are presently applied for the rigorous numerical solution of fully 3-D EM forward problems. I mention the merits and drawbacks of these approaches, and focus on the most essential aspects of numerical implementations, such as preconditioning and solving the resulting systems of linear equations. I refer to some of the most advanced, state-of-the-art, solvers that are today available for such important geophysical applications as induction logging, airborne and controlled-source EM, magnetotellurics, and global induction studies. Then, in the second part of the paper, I review some of the methods that are commonly used to solve 3-D EM inverse problems and analyse current implementations of the methods available. In particular, I also address the important aspects of nonlinear Newton-type optimisation techniques and computation of gradients and sensitivities associated with these problems.

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Section: Integral Equation Approachmentioning

confidence: 96%

Three-Dimensional Electromagnetic Modelling and Inversion from Theory to Application

Avdeev

2005

Surv Geophys

246

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“…The relatively conductive region of the mantle (SE half) is assigned a resistivity of 500 m, whereas the resistive mantle region has a resistivity of 1000 m. The model is rotated clockwise by 45 • to accommodate straight mesh lines at an angle +45 • and −45 • , thereby avoiding edge effects of the rectangular mesh used for the finite difference (FD) modelling (e.g. Cerv & Pek 1990;Avdeev 2005;Börner 2010). MT responses are modelled for the period range 10 −3 -10 5 s at 144 stations arranged in a grid on top of the synthetic model as well as for 13 additional sites aligned along an approximately N-S oriented profile (cf.…”

Section: The Synthetic 3-d Modelmentioning

confidence: 99%

A novel anisotropic inversion approach for magnetotelluric data from subsurfaces with orthogonal geoelectric strike directions

Schmoldt

Jones

2013

Geophysical Journal International

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The key result of this study is the development of a novel inversion approach for cases of orthogonal, or close to orthogonal, geoelectric strike directions at different depth ranges, for example, crustal and mantle depths. Oblique geoelectric strike directions are a well-known issue in commonly employed isotropic 2-D inversion of MT data. Whereas recovery of upper (crustal) structures can, in most cases, be achieved in a straightforward manner, deriving lower (mantle) structures is more challenging with isotropic 2-D inversion in the case of an overlying region (crust) with different geoelectric strike direction. Thus, investigators may resort to computationally expensive and more limited 3-D inversion in order to derive the electric resistivity distribution at mantle depths. In the novel approaches presented in this paper, electric anisotropy is used to image 2-D structures in one depth range, whereas the other region is modelled with an isotropic 1-D or 2-D approach, as a result significantly reducing computational costs of the inversion in comparison with 3-D inversion. The 1-and 2-D versions of the novel approach were tested using a synthetic 3-D subsurface model with orthogonal strike directions at crust and mantle depths and their performance was compared to results of isotropic 2-D inversion. Structures at crustal depths were reasonably well recovered by all inversion approaches, whereas recovery of mantle structures varied significantly between the different approaches. Isotropic 2-D inversion models, despite decomposition of the electric impedance tensor and using a wide range of inversion parameters, exhibited severe artefacts thereby confirming the requirement of either an enhanced or a higher dimensionality inversion approach. With the anisotropic 1-D inversion approach, mantle structures of the synthetic model were recovered reasonably well with anisotropy values parallel to the mantle strike direction (in this study anisotropy was assigned to the mantle region), indicating applicability of the novel approach for basic subsurface cases. For the more complex subsurface cases, however, the anisotropic 1-D inversion approach is likely to yield implausible models of the electric resistivity distribution due to inapplicability of the 1-D approximation. Owing to the higher number of degrees of freedom, the anisotropic 2-D inversion approach can cope with more complex subsurface cases and is the recommended tool for real data sets recorded in regions with orthogonal geoelectric strike directions.

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“…The conventional definition of 'pr,'given by Cagniard (1953), uses the magnitude of MT impedance. In a 2D or 3D inhomogeneous environment the apparent resistivity is frequently distorted by static shifts and other induction effects (Berdichevsky and Dimitriev 1976;Park 1985;Jones 1988;Cerv and Pek 1990, Jiracek 1990, Beamish and Travassos 1992, 1993. In spite of this t|r'e p7data are used directly in computer inversion schemes to determine the resistivity distribution, since the apparent resistivity pseudosection possesses no attribute characteristic in itself suitable for imaging lhe structure.…”

Section: Lntroduction Some Aspects Of the Selection Of Mt Parametermentioning

confidence: 99%

Advances in the combined interpretation of seismics with magnetotellurics¹

Nagy¹

1996

Geophysical Prospecting

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Five examples, obtained during exploration for hydrocarbons in the Pannonian Basin of Hungary, are used to show how the interpretation of seismic sections can be usefully complemented by results from MT surveys.Selection of the most appropriate MT quantities, considered to be proper 'MT attributes' for the purpose of visualization as well as recognition of the subsurface structures and the different inversions of MT data is essential for practical integration of seismic and MT surveys.A new technique providing a semiquantitive MT-attribute pseudosection for the purpose of visualization of the subsurface structures is proposed. The procedure utilizes derivative functions of the phase of MT impedance for visualization and derives estimated depths from the Bostick transformation of Cagniard apparent resistivities.On the basis of the A,{T-attribute pseudosections, constructed from the phase derivatives and transformed resistivity data, depths are estimated for interfaces between geological formations with significant resisti'u'it)' contrast. In particular examples, the interface between the Tertiary sediments and the older basement rocks as well as tectonic fracture zones with decreased resistivitv can be resolved.

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Modelling and analysis of electromagnetic fields in 3D inhomogeneous media

Cited by 19 publications

References 67 publications

Three-Dimensional Electromagnetic Modelling and Inversion from Theory to Application

Three-Dimensional Electromagnetic Modelling and Inversion from Theory to Application

A novel anisotropic inversion approach for magnetotelluric data from subsurfaces with orthogonal geoelectric strike directions

Advances in the combined interpretation of seismics with magnetotellurics¹

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Modelling and analysis of electromagnetic fields in 3D inhomogeneous media

Cited by 19 publications

References 67 publications

Three-Dimensional Electromagnetic Modelling and Inversion from Theory to Application

Three-Dimensional Electromagnetic Modelling and Inversion from Theory to Application

A novel anisotropic inversion approach for magnetotelluric data from subsurfaces with orthogonal geoelectric strike directions

Advances in the combined interpretation of seismics with magnetotellurics1

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Advances in the combined interpretation of seismics with magnetotellurics¹