Inversion of anisotropic magnetotelluric data

Abramovici, F.; Shoham, Yoram

doi:10.1111/j.1365-246x.1977.tb01324.x

Cited by 16 publications

(10 citation statements)

References 20 publications

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“…Abramovici and Shoham (1977) presented an analysis of least squares inversion of anisotropic data, again not ascertaining the stability of the solutions.…”

Section: Inversionmentioning

confidence: 99%

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Inversion of anisotropic MT data using approximate equality constrains

Régis

Luz

Costa

2010

SEG Technical Program Expanded Abstracts 2010

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The application of a priori information to stabilize the inversion of MT data usually has been done in a purely mathematical form, mainly as smoothness constrains that have little regard to the physical and geological conditions that generate the data. We present a stable solution for the anisotropic magnetotelluric inverse problem through the use of approximate equality constraints as a way of including realistic a priori information in the automatic inversion process. Information on the structures of the earth down to a certain depth can be acquired from well log data or other geophysical methods or geological knowledge. If the values of some of the parameters to be found in the inversion were known exactly, we should simply remove those parameters from the inversion process. However, if there is a degree of confidence in that information, but not certainty, then some freedom should be allowed for those parameters to converge to values that are close, but not exactly equal to those of the constraints. Following that idea, we constrain the solution of the inverse problem by imposing the values of the constraints to the inversion parameters in a least squares sense, therefore the term approximate equality.We use this kind of information to constrain our inversion of MT data and we find that we can stabilize the solution for the anisotropic 1-D problem. We demonstrate the method by inverting synthetic data, contaminated by random noise.

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“…Abramovici and Shoham (1977) presented an analysis of least squares inversion of anisotropic data, again not ascertaining the stability of the solutions.…”

Section: Inversionmentioning

confidence: 99%

“…We can use as our observations the apparent resistivities and phases which are drawn from the elements of the impedance tensor, or we can use directly the real and imaginary parts of those elements, which is our choice in this work (a thorough discussion on the advantages of each choice is made in Abramovici & Shoham (1977)). …”

Section: Inversionmentioning

confidence: 99%

Inversion of anisotropic MT data using approximate equality constrains

Régis

Luz

Costa

2010

SEG Technical Program Expanded Abstracts 2010

View full text Add to dashboard Cite

show abstract

“…The determination of parameters in partial differential equations, known as parameter estimation, is generally ill posed and non-unique, and arises in many areas of inverse problems, such as in ground-water modeling 7,54 and geophysics. 1,58 Usually, most models describing a system are nonlinear. Linearizing the problem is achieved by applying a Taylor series expansion to the model function, and the zero-and first-order terms are used, assuming local linearity.…”

Section: Parameter Estimationmentioning

confidence: 99%

Estimation of the Bidomain Conductivity Parameters of Cardiac Tissue From Extracellular Potential Distributions Initiated by Point Stimulation

Graham

Kilpatrick

2010

Ann Biomed Eng

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A method for determining the bidomain conductivity values is developed. The study was generated because the different sets of measured conductivity values reported in the literature each produce significantly different bidomain simulation results. The method involves mapping the propagation of the electrical activation of cardiac tissue, initiated by point stimulation, via extracellular electrodes. A time-dependent bidomain model is used to simulate the electrical phenomena. The optimum set of conductivity values is achieved by minimizing the difference between the bidomain model output and the measured extracellular potential, by means of inverse techniques in parameter estimation least-squares and singular value decomposition. The method is validated with synthetic data with added random noise. Other parameters in the model such as membrane capacitance and fiber angle can also be estimated. The method takes a different approach to the conventional four-electrode technique, as it does not require the small electrode separation needed to separate the extracellular current from the intracellular.

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“…12(b) at depths below 70 km. The theory for calculating the response of models with anisotropic layers has been developed by O'Brien & Morrison (1967), Reddy & Rankin (1975) and Abramovici & Shoham (1977). Electrical anisotropy was suggested as a parameter for investigating deep (up to 700 km) linear structures connected with ocean floor spreading by Stegena, Horvtith & Adam (1971).…”

Section: Anisotropymentioning

confidence: 99%

The conductivity of the crust and mantle beneath the Kapuskasing Uplift: electrical anisotropy in the upper mantle

Kurtz

Craven

Niblett

et al. 1993

Geophysical Journal International

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S U M M A R YThe Kapuskasing Uplift has been interpreted as an oblique cross-section of up to 25km of crust and thus provides the opportunity to examine the properties of exposed mid-to lower-crustal material. A magnetotelluric (MT) survey mapped a remarkably uniform upper crust and provided no evidence for upper crustal conductive zones that could be related to the often observed increase in mid and lower crustal conductivity. The only shallow conductive anomaly is related to the Ivanhoe Lake Cataclastic Zone but its electrical signature does not appear to extend more than one kilometer in depth.A regional apparent resistivity curve was determined from MT data and confirmed by subsequent controlled source electromagnetic surveys. Regional curves are essential for proper structural interpretation but are often difficult to determine because of electric field distortions. The data show a decrease in resistivity at depths below 15 km which is typical of continental crust in many areas of the world.There is a clear difference in orthogonal apparent resistivity and phase curves at periods greater than 10s which is most pronounced in a N65"E and N25"W coordinate frame. Two different models are proposed to explain the data. The first consists of a conducting 2-D slab of approximately 50 km width in the lower crust and striking N65"E. The strike direction is consistent with a number of regional structural trends but there is no other direct supporting evidence for it. The second model invokes either micro or macro electrical anisotropy in the upper mantle. There is considerable evidence for seismic anisotropy in the region. The electrical anisotropy could be the result of preferential conduction along the c-axis of olivine crystals, hydrogen dissolved in the olivine lattice with preferential conduction along the a-axis, or possible alignment of dykes, joints and faults in the upper mantle. If the anisotropy is related to strain induced orientations of crystals or fabric, it will provide evidence for the motions of the mantle associated with plate tectonics.

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Inversion of anisotropic magnetotelluric data

Cited by 16 publications

References 20 publications

Inversion of anisotropic MT data using approximate equality constrains

Inversion of anisotropic MT data using approximate equality constrains

Estimation of the Bidomain Conductivity Parameters of Cardiac Tissue From Extracellular Potential Distributions Initiated by Point Stimulation

The conductivity of the crust and mantle beneath the Kapuskasing Uplift: electrical anisotropy in the upper mantle

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