Occam’s inversion to generate smooth, two‐dimensional models from magnetotelluric data

Groot‐Hedlin, Catherine de; Constable, Steven

doi:10.1190/1.1442813

Cited by 1,284 publications

(593 citation statements)

References 17 publications

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“…The smoothness-constrained least-squares optimization method is frequently used for 2-D and 3-D inversion of resistivity data (deGroot-Hedlin & Constable 1990;Ellis & Oldenburg 1994;Loke et al 2013aLoke et al , 2014b. The 3-D model usually consists of many quadrilateral cells (Loke & Barker 1996).…”

Section: Data Inversion Model Resolution and The 'Compare R' Methodsmentioning

confidence: 99%

Computation of optimized arrays for 3-D electrical imaging surveys

Loke¹,

Wilkinson

Uhlemann

et al. 2014

Geophysical Journal International

120

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S U M M A R Y3-D electrical resistivity surveys and inversion models are required to accurately resolve structures in areas with very complex geology where 2-D models might suffer from artefacts. Many 3-D surveys use a grid where the number of electrodes along one direction (x) is much greater than in the perpendicular direction (y). Frequently, due to limitations in the number of independent electrodes in the multi-electrode system, the surveys use a roll-along system with a small number of parallel survey lines aligned along the x-direction. The 'Compare R' array optimization method previously used for 2-D surveys is adapted for such 3-D surveys. Offset versions of the inline arrays used in 2-D surveys are included in the number of possible arrays (the comprehensive data set) to improve the sensitivity to structures in between the lines. The array geometric factor and its relative error are used to filter out potentially unstable arrays in the construction of the comprehensive data set. Comparisons of the conventional (consisting of dipole-dipole and Wenner-Schlumberger arrays) and optimized arrays are made using a synthetic model and experimental measurements in a tank. The tests show that structures located between the lines are better resolved with the optimized arrays. The optimized arrays also have significantly better depth resolution compared to the conventional arrays.

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Section: Data Inversion Model Resolution and The 'Compare R' Methodsmentioning

confidence: 99%

Computation of optimized arrays for 3-D electrical imaging surveys

Loke¹,

Wilkinson

Uhlemann

et al. 2014

Geophysical Journal International

120

View full text Add to dashboard Cite

show abstract

“…in terms of its first and second derivatives) have been considered by Constable et al (1987) and by Smith and Booker (1988). For 2-D MT inversion, deGroot-Hedlin and Constable (1990) implemented a minimum-structure inversion which is referred to as OCCAM and is based on the finite-element forward solution of Wannamaker et al (1987). A more rapid 2-D MT inversion called the Rapid Relaxation Inverse has also been developed by Smith and Booker (1991).…”

Section: Regularised Inversionmentioning

confidence: 99%

“…A more rapid 2-D MT inversion called the Rapid Relaxation Inverse has also been developed by Smith and Booker (1991). Here we use the 2-D OCCAM procedure, described in detail by deGroot-Hedlin and Constable (1990), which has proved to be a very stable algorithm.…”

Section: Regularised Inversionmentioning

confidence: 99%

Two-dimensional, regularised inversion of VLF data

Beamish

1994

Journal of Applied Geophysics

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Very low frequency electromagnetic (EM) methods using VLF transmitters have found many applications in subsurface geophysical investigations. Surface measurements involving both the vertical component of the magnetic field (VLF-EM or VLF-Z) and of the apparent resistivity (VLF-R) are increasingly common. Although extensive VLF data sets have been successfully used for mapping purposes, modelling and interpretation techniques which assess the third (i.e. depth) dimension appear limited. Given a profile of VLF-R measurements the main purpose of the present study is to demonstrate an automatic method for the construction of a resistivity cross-section. The technique used is one of a new generation of regularised inversion methods. These techniques attempt to overcome the problem of equivalence/non-uniqueness in EM sounding data by constructing the resistivity distribution with the minimum amount of structure that fits the data. VLF data represent a special case of plane-wave EM sounding in that they conform, in practice, to a single-frequency technique. This fact imposes a limitation in the amount of vertical resolution that we can expect using such data. In the case of two-dimensional modelling and inversion, resolution through the cross-section is a resultant attribute from both vertical and lateral resistivity gradients within the subsurface. In order to provide insight into the practical application of regularised inversion techniques to VLF data, both synthetic and field examples are considered. Both sets of examples are primarily concerned with VLF data applied to near-surface fault mapping where the main aim is to assess the location, dip and depth extent of conductive subsurface features.2

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“…The minimization problem (15) gives us the regularized weighted least squares solution to the inverse problem. Note that practically all existing inversion methods (see, for example, OCCAM MT inversion by de Groot-Hedlin and Constable [1990] or gravity and magnetic inversion by Li and Oldenburg [1998]) use the weighting of the model parameters in one or another form. However, the weights are usually selected on the basis of some simple assumptions about the variation of the sensitivity with the depth to the target.…”

Section: Formulation Of the Weighted Inverse Solutionmentioning

confidence: 99%

Two‐dimensional magnetotelluric inversion of blocky geoelectrical structures

Mehanee

Zhdanov

2002

J. Geophys. Res.

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[1] This paper demonstrates that there are alternative approaches to the magnetotelluric (MT) inverse problem solution based on different types of geoelectrical models. The traditional approach uses smooth models to describe the conductivity distribution in underground formations. In this paper, we present a new approach, based on approximating the geology by models with blocky conductivity structures. We can select one or another class of inverse models by choosing between different stabilizing functionals in the regularization method. The final decision, whose approach may be used for the specific MT data set, is made on the basis of available geological information. This paper describes a new way of stabilizing two-dimensional MT inversion using a minimum support functional and shows the improvement that it provides over traditional methods for geoelectrical models with blocky structures. The new method is applied to MT data collected for crustal imaging in the Carrizo Plain in California and to MT data collected for mining exploration by INCO Exploration.

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Occam’s inversion to generate smooth, two‐dimensional models from magnetotelluric data

Cited by 1,284 publications

References 17 publications

Computation of optimized arrays for 3-D electrical imaging surveys

Computation of optimized arrays for 3-D electrical imaging surveys

Two-dimensional, regularised inversion of VLF data

Two‐dimensional magnetotelluric inversion of blocky geoelectrical structures

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