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Wilhelms, Wenke. "Development of a three-dimensional all-at-once inversion approach for the magnetotelluric method." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2016. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-207548.
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A three-dimensional inversion was implemented for magnetotellurics, which is a passive electromagnetic method in geophysics. It exploits natural electromagnetic fields of the Earth, which function as sources. Their interaction with the conductive parts of the subsurface are registered when components of the electric and the magnetic field are measured and evaluated.
The all-at-once approach is an inversion scheme that is relatively new to geophysics. In this approach, the objective function – the basis of each inversion – is called the Lagrangian. It consists of three parts: (i) the data residual norm, (ii) the regularisation part, and (iii) the forward problem. The latter is the significant difference to conventional inversion approaches that are built up of a forward calculation part and an inversion part. In the case of all-at-once, the forward problem is incorporated in the objective function and is therefore already taken into account in each inversion iteration. Thus, an explicit forward calculation is obsolete. As an objective function, the Lagrangian shall reach a minimum and therefore its first and second derivatives are evaluated. Hence, the gradient of the Lagrangian and its Hessian are constituent parts of the KKT system – the Newton-type system that is set up in the all-at-once inversion. Conventional inversion approaches avoid the Hessian because it is a large, dense, not positive definite matrix that is challenging to handle. However, it provides additional information to the inversion, which raises hope for a high quality inversion result.
As a first step, the inversion was programmed for the more straightforward one-dimensional magnetotelluric case. This was particularly suitable to become familiar with sQMR – a Krylov subspace method which is essential for the three-dimensional case to be able to work with the Hessian and the resulting KKT system. After the implementation and validation of the one-dimensional forward operator, the Lagrangian and its derivatives were set up to complete the inversion, which successfully solved the KKT system. Accordingly, the three-dimensional forward operator also needed to be implemented and validated, which was done using published data from the 3D-2 COMMEMI model. To realise the inversion, the Lagrangian was assembled and its first and second derivatives were validated with a test that exploits the Taylor expansion. Then, the inversion was initially programmed for the Gauss-Newton approximation where second order information is neglected. Since the system matrix of the Gauss-Newton approximation is positive definite, the solution of this system of equations could be carried out by the conventional solver pcg. Based on that, the complete KKT system (Newton\\\'s method) was set up and preconditioned sQMR solved this system of equations.
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Chen, Xiaoming. "Two-dimensional constrained anisotropic inversion of magnetotelluric data." Phd thesis, Universität Potsdam, 2012. http://opus.kobv.de/ubp/volltexte/2012/6316/.
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Tectonic and geological processes on Earth often result in structural anisotropy of the subsurface, which can be imaged by various geophysical methods. In order to achieve appropriate and realistic Earth models for interpretation, inversion algorithms have to allow for an anisotropic subsurface. Within the framework of this thesis, I analyzed a magnetotelluric (MT) data set taken from the Cape Fold Belt in South Africa. This data set exhibited strong indications for crustal anisotropy, e.g. MT phases out of the expected quadrant, which are beyond of fitting and interpreting with standard isotropic inversion algorithms. To overcome this obstacle, I have developed a two-dimensional inversion method for reconstructing anisotropic electrical conductivity distributions.
The MT inverse problem represents in general a non-linear and ill-posed minimization problem with many degrees of freedom: In isotropic case, we have to assign an electrical conductivity value to each cell of a large grid to assimilate the Earth's subsurface, e.g. a grid with 100 x 50 cells results in 5000 unknown model parameters in an isotropic case; in contrast, we have the sixfold in an anisotropic scenario where the single value of electrical conductivity becomes a symmetric, real-valued tensor while the number of the data remains unchanged. In order to successfully invert for anisotropic conductivities and to overcome the non-uniqueness of the solution of the inverse problem it is necessary to use appropriate constraints on the class of allowed models. This becomes even more important as MT data is
not equally sensitive to all anisotropic parameters. In this thesis, I have developed an algorithm through which the solution of the anisotropic inversion problem is calculated by minimization of a global penalty functional consisting of three entries: the data misfit, the model roughness constraint and the anisotropy constraint. For comparison, in an isotropic approach only the first two entries are minimized. The newly defined anisotropy term is measured by the sum of the square difference of the principal conductivity values of the model. The basic idea of this constraint is straightforward. If an isotropic model is already adequate to explain the data, there is no need to introduce electrical anisotropy at all.
In order to ensure successful inversion, appropriate trade-off parameters, also known as regularization parameters, have to be chosen for the different model constraints. Synthetic tests show that using fixed trade-off parameters usually causes the inversion to end up by either a smooth model with large RMS error or a rough model with small RMS error. Using of a relaxation approach on the regularization parameters after each successful inversion iteration will result in smoother inversion model and a better convergence. This approach seems to be a sophisticated way for the selection of trade-off parameters. In general, the proposed inversion method is adequate for resolving the principal conductivities defined in horizontal plane. Once none of the principal directions of the anisotropic structure is coincided with the predefined strike direction, only the corresponding effective conductivities, which is the projection of the principal conductivities onto the model coordinate axes direction, can be resolved and the information about the rotation angles is
lost.
In the end the MT data from the Cape Fold Belt in South Africa has been analyzed. The MT data exhibits an area (> 10 km) where MT phases over 90 degrees occur. This part of data cannot be modeled by standard isotropic modeling procedures and hence can not be properly interpreted. The proposed inversion method, however, could not reproduce the anomalous large phases as desired because of losing the information about rotation angles. MT phases outside the first quadrant are usually obtained by different anisotropic anomalies with oblique anisotropy strike. In order to achieve this challenge, the algorithm needs further developments. However, forward modeling studies with the MT data have shown that surface highly conductive heterogeneity in combination with a mid-crustal electrically anisotropic zone are required to fit the data. According to known geological and tectonic information the mid-crustal zone is interpreted as a deep aquifer related to the fractured Table Mountain Group rocks in the Cape Fold Belt.<br>Tektonische und geologische Prozesse verursachen häufig eine strukturelle Anisotropie des Untergrundes, welche von verschiedenen geophysikalischen Methoden beobachtet werden kann. Zur Erstellung und Interpretation geeigneter, realistischer Modelle der Erde sind Inversionsalgorithmen notwendig, die einen anisotropen Untergrund einbeziehen können. Für die vorliegende Arbeit habe ich einen magnetotellurischen (MT) Datensatz vom Cape Fold Gürtel in Südafrika untersucht. Diese Daten weisen auf eine ausgeprägte Anisotropie der Kruste hin, da z.B. die MT Phasen außerhalb des erwarteten Quadranten liegen und nicht durch standardisierte isotrope Inversionsalgorithmen angepasst und ausgewertet werden können. Um dieses Problem zu beheben, habe ich eine zweidimensionale Inversionsmethode entwickelt, welche eine anisotrope elektrische Leitfähigkeitsverteilungen in den Modellen zulässt.
Die MT Inversion ist im allgemeinen ein nichtlineares, schlecht gestelltes Minimierungsproblem mit einer hohen Anzahl an Freiheitsgraden. Im isotropen Fall wird jeder Gitterzelle eines Modells ein elektrischer Leitfähigkeitswert zugewiesen um den Erduntergrund nachzubilden. Ein Modell mit beispielsweise 100 x 50 Zellen besitzt 5000 unbekannte Modellparameter. Im Gegensatz dazu haben wir im anisotropen Fall die sechsfache Anzahl, da hier aus dem einfachen Zahlenwert der elektrischen Leitfähigkeit ein symmetrischer, reellwertiger Tensor wird, wobei die Anzahl der Daten gleich bleibt. Für die erfolgreiche Inversion von anisotropen Leitfähigkeiten und um die Nicht-Eindeutigkeit der Lösung des inversen Problems zu überwinden, ist eine geeignete Einschränkung der möglichen Modelle absolut notwendig. Dies wird umso wichtiger, da die Sensitivität von MT Daten nicht für alle Anisotropieparameter gleich ist. In der vorliegenden Arbeit habe ich einen Algorithmus entwickelt, welcher die Lösung des anisotropen Inversionsproblems unter Minimierung einer globalen Straffunktion berechnet. Diese besteht aus drei Teilen: der Datenanpassung, den Zusatzbedingungen an die Glätte des Modells und die Anisotropie. Im Gegensatz dazu werden beim isotropen Fall nur die ersten zwei Parameter minimiert. Der neu definierte Anisotropieterm wird mit Hilfe der Summe der quadratischen Abweichung der Hauptleitfähigkeitswerte des Modells gemessen. Die grundlegende Idee dieser Zusatzbedingung ist einfach. Falls ein isotropes Modell die Daten ausreichend gut anpassen kann, wird keine elektrische Anisotropie zusätzlich in das Modell eingefügt.
Um eine erfolgreiche Inversion zu garantieren müssen geeignete Regularisierungsparameter für die verschiedenen Nebenbedingungen an das Modell gewählt werden. Tests mit synthetischen Modellen zeigen, dass bei festgesetzten Regularisierungsparametern die Inversion meistens entweder in einem glatten Modell mit hohem RMS Fehler oder einem groben Modell mit kleinem RMS Fehler endet. Die Anwendung einer Relaxationsbedingung auf die Regularisierung nach jedem Iterationsschritt resultiert in glatteren Inversionsmodellen und einer höheren Konvergenz und scheint ein ausgereifter Weg zur Wahl der Parameter zu sein. Die vorgestellte Inversionsmethode ist im allgemeinen in der Lage die Hauptleitfähigkeiten in der horizontalen Ebene zu finden. Wenn keine der Hauptrichtungen der Anisotropiestruktur mit der vorgegebenen Streichrichtung übereinstimmt, können nur die dazugehörigen effektiven Leitfähigkeiten, welche die Projektion der Hauptleitfähigkeiten auf die Koordinatenachsen des Modells darstellen, aufgelöst werden. Allerdings gehen die Informationen über die Rotationswinkel verloren.
Am Ende meiner Arbeit werden die MT Daten des Cape Fold Gürtels in Südafrika analysiert. Die MT Daten zeigen in einem Abschnitt des Messprofils (> 10 km) Phasen über 90 Grad. Dieser Teil der Daten kann nicht mit herkömmlichen isotropen Modellierungsverfahren angepasst und daher mit diesen auch nicht vollständig ausgewertet werden. Die vorgestellte Inversionsmethode konnte die außergewöhnlich hohen Phasenwerte nicht wie gewünscht im Inversionsergebnis erreichen, was mit dem erwähnten Informationsverlust der Rotationswinkel begründet werden kann. MT Phasen außerhalb des ersten Quadranten können für gewöhnlich bei Anomalien mit geneigter Streichrichtung der Anisotropie gemessen werden. Um diese auch in den Inversionsergebnissen zu erreichen ist eine Weiterentwicklung des Algorithmus notwendig. Vorwärtsmodellierungen des MT Datensatzes haben allerdings gezeigt, dass eine hohe Leitfähigkeitsheterogenität an der Oberfläche in Kombination mit einer Zone elektrischer Anisotropie in der mittleren Kruste notwendig sind um die Daten anzupassen. Aufgrund geologischer und tektonischer Informationen kann diese Zone in der mittleren Kruste als tiefer Aquifer interpretiert werden, der im Zusammenhang mit den zerrütteten Gesteinen der Table Mountain Group des Cape Fold Gürtels steht.
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Hoffmann-Rothe, Arne. "Combined structural and magnetotelluric investigation across the West Fault Zone in northern Chile." Phd thesis, [S.l.] : [s.n.], 2002. http://pub.ub.uni-potsdam.de/2002/0025/ahoro.pdf.
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Franke-Börner, Antje. "Three-dimensional finite element simulation of magnetotelluric fields on unstructured grids." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2013. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-114985.
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In der vorliegenden Arbeit werden verschiedene Randwertprobleme zur Beschreibung der Ausbreitung magnetotellurischer Felder mit Hilfe der Finite-Elemente-Methode numerisch gelöst. Die zwei- und dreidimensionalen Randwertprobleme zur Simulation des elektrischen oder des magnetischen Feldes, des magnetischen Vektorpotentials und des elektrischen Skalarpotentials, des magnetischen Vektorpotentials allein oder des anomalen magnetischen Vektorpotentials werden aus den Maxwell-Gleichungen hergeleitet. Auf Grundlage von Anwendung der Konvergenztheorie auf die Finite-Elemente-Lösung werden Konvergenzstudien für zweidimensionale Modelle des homogenen und des geschichteten Halbraums sowie für das dreidimensionale COMMEMI 3-D-2-Modell durchgeführt. Diese werden genutzt, um die Randwertprobleme hinsichtlich ihrer Effizienz zu bewerten. Außerdem liefern Konvergenzstudien eine Abschätzung des lokalen Fehlers der numerischen Lösung für ein realitätsnahes Modell des Vulkans Stromboli und seiner Umgebung, welches digitale Geländedaten enthält<br>This thesis presents the numerical finite-element solution of different formulations of the magnetotelluric boundary value problem. Based on Maxwell\'s equations, the two-dimensional and three-dimensional boundary value problems are derived in terms of the electric or the magnetic field, the magnetic vector and the electric scalar potential, the magnetic vector potential only, or the anomalous magnetic vector potential. To evaluate their efficiency, convergence studies are performed for the two-dimensional models of the homogeneous and the layered halfspace as well as for the COMMEMI-3-D-2 model. Moreover, convergence studies yield estimates of the local error of the numerical solution for a close-to-reality model of Stromboli volcano incorporating digital terrain data
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Recher, Stephan. "Dreidimensionale Erkundung von Altlasten mit Radio-Magnetotellurik Vergleiche mit geophysikalischen, geochemischen und geologischen Analysen an Bodenproben aus Rammkernsondierungen /." [S.l. : s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=965795594.
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Maercklin, Nils. "Seismic structure of the Arava Fault, Dead Sea Transform." Phd thesis, [S.l.] : [s.n.], 2004. http://pub.ub.uni-potsdam.de/2004/0046/marcklin.pdf.
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Müller, Andreas [Verfasser]. "Magnetotellurik zur Identifizierung von tektonisch verursachten Änderungen des elektrischen Widerstandes : Modellierungen und neue Methoden der Auswertung ; ein Beitrag zum Deutsch-Türkischen Erdbeben-Forschungsprojekt / Andreas Müller. Deutsches GeoForschungsZentrum GFZ." Potsdam : Deutsches GeoForschungsZentrum GFZ, 2012. http://d-nb.info/1023445506/34.
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Medin, Ashley E. "The magnetotelluric inverse problem." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2008. http://wwwlib.umi.com/cr/ucsd/fullcit?p3336606.
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Thesis (Ph. D.)--University of California, San Diego, 2008.<br>Title from first page of PDF file (viewed January 5, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 202-208).
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Fridlund, Julia. "Processing of Noisy Controlled Source Audio Magnetotelluric (CSAMT) Data." Thesis, Uppsala universitet, Geofysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-396255.
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Controlled Source Audio Magnetotellurics (CSAMT) is a geophysical method for characterizing the resistivity of the subsurface with the help of electromagnetic waves. The method is used for various purposes, such as geothermal- and hydrocarbon exploration, mineral prospecting and for investigation of groundwater resources. Electromagnetic fields are created by running an alternating current in a grounded electric dipole and by varying the frequency, different depths can be targeted. Orthogonal components of the electromagnetic fields are measured at receiver stations a few kilometers away from the source. From these field components, so called magnetotellurics transfer functions are estimated, which can be used to invert for the resistivity of the subsurface. The data used in this project is from a survey conducted in 2014 and 2016 in Kiruna by Uppsala University and the mining company LKAB. Measurements were made at 31 stations along two orthogonal profiles. The data have been processed earlier, but due to noise, especially in the lower frequencies, a significant part of the data set could not be inverted. The aim of this project was to improve the results by analyzing the data and testing different methods to remove noise. First, robust regression was used to account for possible non-Gaussian noise in the estimation of the magnetotelluric transfer functions. Except for one station on profile 1, the robust method did not improve the results, which suggests that the noise is mostly Gaussian. Then modified versions of least squares, each affected by a different bias, were used to estimate the transfer functions. Where there is more noise, the estimates should differ more due to their different biases. The estimates differed most for low frequencies and especially on the part of profile 2 that was measured in 2014. It was investigated whether the railway network could explain part of the low frequency noise. Measures were taken to reduce spectral leakage from the railway signal at 16 ⅔ Hz to the closest transmitter frequencies 14 Hz and 20 Hz, but no clear improvement was seen and more detailed studies need to be conducted to determine this matter. Finally, a method based on comparing the ratio of short-term and long-term averages was tested to remove transients in the measured time series of the electromagnetic field components. This proved difficult to implement due to the variability of the time series’ behavior between different stations, frequencies and field components. However, the method showed some potential for stations 9 and 10 on profile 1, and could probably be developed further to remove transients more efficiently and thus improve the data.<br>Magnetotellurik med kontrollerad källa (förkortat CSAMT på engelska) är en metod där elektromagnetiska fält används för att undersöka markens resistivitet. Resisitivitet är ett mått på hur bra eller dåligt marken leder elektriska strömmar. Metoden används till exempel för att mäta djupet till berggrunden, som oftast har högre resistivitet (sämre ledningsförmåga) än marken ovanför. Man kan också hitta metaller, så som guld och koppar, vilka har väldigt låg resistivitet (bra ledningsförmåga). Elektromagnetiska vågor skapas genom att man låter en växelström gå igenom en lång ledning. Vågorna färdas först genom luften och sen ner i marken. Hur djupt ner de når beror på växelströmmens frekvens; med låga frekvenser når vågorna djupare ner i marken än med höga. Under markytan inducerar de elektromagnetiska vågorna elektriska strömmar, så kallade telluriska strömmar (dvs. jordströmmar). Strömmarna blir svagare ju längre de färdas och hur snabbt de avtar i styrka beror på jordens resistivitet. Strömmarna skapar också nya elektriska och magnetiska fält som färdas tillbaka mot ytan. Vid markytan mäter man fältens styrka för olika frekveser, vilket då ger information om resistiviteten på olika djup. Från mätningarna tar man ofta fram så kallade magnetotelluriska överföringsfunktioner. Dessa överföringsfunktioner gör det lättare att tolka datan och ta reda på resistiviteten hos marken. I detta projekt har CSAMT-data använts från en undersökning i Kiruna som genomfördes av Uppsala Universitet och gruvföretaget LKAB. Datan har bearbetats tidigare, men på grund av mycket brus i mätningarna blev inte resultatet så bra som väntat. Brus kan komma från allt som genererar elektromagnetiska fält, till exempel elledningar, tågledningar eller naturliga variationer i jordens egna magnetfält. Målet med projektet var att förbättra resultatet genom att analysera datan och testa olika metoder för att ta bort brus. Den vanligaste metoden för att beräkna överföringsfunktionerna antar att det magnetiska fältet är fritt från brus. Detta är inte nödvändigtvis sant och kan leda till bias, alltså ett snedvridet resultat. Andra sätt att beräkna överföringsfunktionerna på ger olika bias. Det här kan man utnyttja för att se hur mycket brus som finns i datan. Om det inte finns något brus alls så blir alla överföringsfunktioner lika, medan om det finns mycket brus så skiljer de sig mer åt. På detta sätt upptäcktes att det var mer brus för frekvenserna 14 och 20 Hz (där 1 Hz är 1 svängning per sekund). En förklaring till det kan vara att tågledningar, som genererar elektromagnetiska fält med 16.67 Hz, ligger nära i frekvens och stör dessa signaler. För att minska brusets påverkan testades så kallad robust processering. Det innebär att man lägger mindre vikt vid de mätningar som tycks vara mycket annorlunda (alltså innehåller mer brus) från andra mätningar. Tyvärr så hjälpte inte denna strategi nämnvärt för att förbättra resultatet. Till sist tog vi fram en metod för att ta bort transienter, vilket är kortvarigt brus med hög intensitet. Transienter kan till exempel komma från åskblixtar, som ju är kortvariga elektriska urladdningar. Det visade sig dock att detta inte var helt enkelt, då det var svårt att se vad som var brus och vad som bara var naturliga variationer hos de elektromagnetiska fälten. Men i några fall kunde bruset urskiljas och därför verkar det troligt att fortsatt arbete med denna metod skulle kunna ge ännu bättre resultat.
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Neukirch, Maik. "Non Stationary Magnetotelluric Data Processing." Doctoral thesis, Universitat de Barcelona, 2014. http://hdl.handle.net/10803/284932.
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Studies have proven that the desired signal for Magnetotellurics (MT) in the electromagnetic (EM) field can be regarded as 'quasi stationary' (i.e. sufficiently stationary to apply a windowed Fourier transform). However, measured time series often contain environmental noise. Hence, they may not fulfill the stationarity requirement for the application of the Fourier Transform (FT) and therefore may lead to false or unreliable results under methods that rely on the FT. In light of paucity of algorithms of MT data processing in the presence of non stationary noise, it is the goal of this thesis to elaborate a robust, non stationary algorithm, which can compete with sophisticated, state-of-the-art algorithms in terms of accuracy and precision. In addition, I proof mathematically the algorithm's viability and validate its superiority to other codes processing non stationary, synthetic and real MT data.
Non stationary EM data may affect the computation of Fourier spectra in unforeseeable manners and consequently, the traditional estimation of the MT transfer functions (TF). The TF estimation scheme developed in this work is based on an emerging nonlinear, non stationary time series analysis tool, called Empirical Mode Decomposition (EMD). EMD decomposes time series into Intrinsic Mode Functions (IMF) in the time-frequency domain, which can be represented by the instantaneous parameters amplitude, phase and frequency. In the first part of my thesis, I show that time slices of well defined IMFs equal time slices of Fourier Series, where the instantaneous parameters of the IMF define amplitude and phase of the Fourier Series parameters. Based on these findings I formulate the theorem that non stationary convolution of an IMF with a general time domain response function translates into a multiplication of the IMF with the respective spectral domain response function, which is explicitly permitted to vary over time. Further, I employ real world MT data to illustrate that a de-trended signal's IMFs can be convolved independently and then be used for further time-frequency analysis as done for MT processing.
In the second part of my thesis, I apply the newly formulated theorem to the MT method. The MT method analyses the correlation between the electric and magnetic field due to the conductivity structure of the subsurface. For sufficiently low frequencies (i.e. when the EM field interacts diffusively), the conductive body of the Earth acts as an inductive system response, which convolves with magnetic field variations and results in electric field variations. The frequency representation of this system response is commonly referred to as MT TF and its estimation from measured electric and magnetic time series is summarized as MT processing. The main contribution in this thesis is the design of the MT TF estimation algorithm based on EMD. In contrast to previous works that employ EMD for MT data processing, I (i) point out the advantages of a multivariate decomposition, (ii) highlight the possibility to use instantaneous parameters, and (iii) define the homogenization of frequency discrepancies between data channels. In addition, my algorithm estimates the transfer functions using robust statistical methods such as (i) robust principal component analysis and (ii) iteratively re-weighted least squares regression with a Huber weight function. Finally, TF uncertainties are estimated by iterating the complete robust regression, including the robust weight computation, by means of a bootstrap routine.
The proposed methodology is applied to synthetic and real data with and without non stationary character and the results are compared with other processing techniques. I conclude that non stationary noise can heavily affect Fourier based MT data processing but the presented non stationary approach is nonetheless able to extract the impedances correctly even when the other methods fail.
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Nascimento, Darcy. "Magnetotelluric instrument development and application." Thesis, University of Edinburgh, 1997. http://hdl.handle.net/1842/15488.
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The magnetotelluric method (MT) has been used to study the conductivity structure of the earth. The method uses the time variations of the natural magnetic and the induced electric fields measured simultaneously at the earth's surface. The demand for new MT instrumentation has increased in the past few years. New applications require more complex sensor configurations. Characteristics like size, weight and real time data processing have become increasingly important to improve logistics and mobility, although it is becoming more and more difficult to measure electromagnetic fields without strong contamination from <I>man-made</I> sources. The ability to process MT results in the field is essential for a quick evaluation of the site conditions, enabling the time required to obtain a suitable amount of good quality data to be reduced. SPAM Mk-III (Short-Period Automatic Magnetotelluric) developed at The Edinburgh University introduces new concepts in terms of geophysical instrumentation. The equipment is based on a family of Transputer devices widely used in parallel processing, incorporating the recent technologies and techniques. Its modular design allows flexible network configurations. A complete description of the equipment, design concepts, features and the precautions needed in designing low-noise instrumentation are presented in this thesis. The distinctive SPAM Mk-III capabilities of multi-channel data acquisition were used in two field experiments. In the first experiment the effect of the electric dipole length on the impedance tensor was investigated. Results confirmed that the apparent resistivity and phase are quite consistent and that longer electric dipoles tended to be more susceptible to local interference. In the second experiment the rotation property of the impedance tensor was studied. The experiment reinforces the assumption that for a layered earth (1-D), the impedance tensor is independent of measuring co-ordinates. New Cu-CuSO<SUB>4</SUB> electrodes were developed for the field work. These are to operate in the frequency range of the SPAM Mk-III (0.001 Hz to 2kHz). Several electrodes were tested and the results indicate that noise and stability does not depend on the internal resistance. Also the frequency response of these electrodes show they do not present any filter effects within the range of magnetotelluric application.
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McNeice, Gary Wayne. "Magnetotelluric investigation of the Appalachians, Newfoundland, Canada." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0026/MQ36152.pdf.
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Bennett, Brian R. (Brian Robert). "A long-period magnetotelluric study in California." Thesis, Massachusetts Institute of Technology, 1985. http://hdl.handle.net/1721.1/57627.
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Okazaki, Tomohisa. "Characteristics of Electrical Anisotropy in Magnetotelluric Responses." Kyoto University, 2018. http://hdl.handle.net/2433/232256.
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Whittall, Kenneth Patrick. "Exploring magnetotelluric nonuniqueness using inverse scattering methods." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/27563.
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I present two algorithms which solve the one-dimensional magnetotelluric (MT) problem of finding the electrical conductivity σ(z) as a function of depth in the earth. Together, these algorithms restrict and explore the nonuniqueness of the nonlinear MT inverse problem. They accept constraints which limit the space of acceptable conductivity models and they construct diverse classes of σ(z) in order to explore this space. To avoid pitfalls during interpretation, it is essential to investigate the extent of the nonuniqueness permitted by the MT data.
Algorithm 1 is a two-stage process based on the inverse scattering theory of Weidelt. The first stage uses the MT frequency-domain data to construct an impulse response analogous to a deconvolved seismogram. Since this is a linear problem (a Laplace transform), numerous impulse responses may be generated by linear inverse techniques which handle data errors robustly. I minimize four norms of the impulse response in order to construct varied classes of limited structure models. Two least-squares norms minimize the energy in the impulse response or the energy in its derivative with respect to depth. Two least absolute value norms minimize the magnitudes of the response or its derivative. It is possible to use other norms. The different classes sample the range of acceptable models and the minimum structure criterion is unlikely to allow models with spurious features.
The second stage of Algorithm 1 constructs the conductivity model from the impulse response using any of four Fredholm integral equations of the second kind. I evaluate the performance of each of the four mappings and recommend the Burridge and Gopinath-Sondhi formulations. I also evaluate three approximations to the second-stage equations. One of these is equivalent to the Born approximation which assumes the impulse response has negligible multiple reflections. The approximation that includes first-order multiple reflections is the most accurate and gives conductivity models similar to those given by the integral equations.
Algorithm 2 solves an integral form of a nonlinear Riccati equation relating the measured frequency-domain data to a function of the conductivity. The iterative solution scheme sacrifices the efficiency of a direct inversion process such as Algorithm 1 for the advantages of incorporating localized conductivity constraints. The linear programming formulation readily accepts a wide variety of equality and inequality constraints on σ(z). I use these constraints in two ways to combat the nonuniqueness of this nonlinear inverse problem. First, I impose physical constraints derived from external sources to restrict the nonuniqueness and construct σ(z) models that are closer to reality. Second, I impose constraints specifically designed to estimate the extent ofthe nonuniqueness and explore the range of acceptable σ(z) profiles. The first technique enhances the reliability of an interpretation and the second assesses the plausibility of particular conductivity features. The convergence of Algorithm 2 is good because Algorithm 1 provides varied initial σ(z) which already fit the data well.<br>Science, Faculty of<br>Earth, Ocean and Atmospheric Sciences, Department of<br>Graduate
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Sule, Peter Ojo. "A broadband magnetotelluric investigation in southeast Scotland." Thesis, University of Edinburgh, 1985. http://hdl.handle.net/1842/14514.
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Volti, Theodora. "A magnetotelluric survey in Methana Peninsula (Greece)." Thesis, University of Edinburgh, 1996. http://hdl.handle.net/1842/14614.
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As a first deep geophysical survey, thirteen magnetotelluric (MT) and magnetovariation (MV) soundings in the period range of 0.0085 - 6000 s have been carried out in the Methana Peninsula and Trizina area (Greece) which form a part of the active Hellenic Volcanic Arc (HVA). The intensity of artificial disturbances in Methana prevented the acquisition of good quality data, and led to the exclusion of data in the 10-100 s range from further interpretation. The measured data are first processed using robust methods, then decomposed using the methods of Groom and Bailey and of Bahr. Thin sheet modelling follows with the aim of detecting effects due to the surrounding seas. All the data show anisotropy and were found to be distorted by galvanic distortion, facts which become more apparent at periods below 1 s. At the same period, effects from the sea also become important. The above problems indicated: (i) the insufficiency of 1-D modelling (ii) that the data are at least 2-D and (iii) that a careful consideration of all the above effects must be given in order to provide a meaningful electrical model. The analysis of distortion effects and the measured induction arrows enable the determination of a regional azimuth to which subsequently the data are rotated. Seven sites are used, and a 2-D model is proposed. The model indicates a zone of high conductivity (7-32 ohm m) beneath the centre of the peninsula at a depth of 1-5 km, which is interpreted as being connected with the volcanic history of Methana, as a remaining and cooling part of former magmatic activity. Although with the long period MT data it was not possible to locate a deep magma source connected with the indicated anomaly, induction arrows at T > 2400 s taken from the regional area point towards the South and South West, perpendicular to the strike of the well known deep structure of the Hellenic Volcanic Arc. Further attempts to integrate the results from Methana with other areas along the HVA lead to correlation of the regional azimuths with horizontal stress directions in the South Aegean sea.
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Selway, Katherine Mary. "Two-dimensional magnetotelluric responses of three-dimensional bodies /." Title page, table of contents and abstract only, 2002. http://web4.library.adelaide.edu.au/theses/09SB/09sbs469.pdf.
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Lu, Xinyou. "Inversion of controlled-source audio-frequency magnetotelluric data /." Thesis, Connect to this title online; UW restricted, 1999. http://hdl.handle.net/1773/6799.
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Alvarez, Aramberri Julen. "hp-Adaptive Simulation and Inversion of Magnetotelluric Measurements." Thesis, Pau, 2015. http://www.theses.fr/2015PAUU3056/document.
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La magnéto-tellurique (MT) (Cagniard 1953, Tikhonov 1950) est une technique d'exploration de la Terre basée sur des mesures de champs électromagnétiques (EM). Une source naturelle (non artificielle) harmonique en temps et située dans l'ionosphère (Weaver 1994) produit un champ EM régi par les équations de Maxwell. Les champs électromagnétiques sont enregistrés par plusieurs récepteurs placés sur la surface de la Terre. Ces mesures sont utilisées pour produire une image du sous-sol à partir d'un procédé d'inversion utilisant des méthodes numériques. Nous utilisons la méthode hp-FEM résultant d'une extension du travail de Demkowicz 2005. Nous avons développé un logiciel qui résout, pour la première fois, le problème MT avec des éléments finis auto-adaptatifs. La méthode hp-FEM permet des raffinements locaux, à la fois en taille h et en ordre p sur les éléments, ce qui est un avantage notoire puisque la combinaison de ces deux types de critères permet de mieux capter la présence de singularités, fournissant ainsi des erreurs de discrétisation faible. C'est donc une méthode très précise dont la convergence est exponentielle (Gui and Babuska 1986, Babuska and Guo 1996). En raison des défis d'implémentation encore non résolus (Demkowicz et al. 2002) et de la complexité technique des calculs hp-FEM en 3D, nous nous limitons, dans ce travail, à des calculs en 1D et 2D.Le domaine de calcul est tronqué par un matériau absorbant (Perfectly Matched Layer PML, Berenger 1994), qui est conçu pour s'adapter automatiquement aux propriétés physiques des matériaux. En particulier, il s'ajuste efficacement à l'interface air-sol, où le contraste entre la conductivité des matériaux atteint jusqu'à seize ordres de grandeur. Dans cette thèse, nous présentons également des résultats préliminaires pour la mise en place d'une technique dimensionnelle adaptative plus connue sous le nom de DAM (Dimensionally Adaptive Method (DAM)). Lorsque la distribution de la résistivité du sous-sol dépend de multiples variables spatiales, une analyse correcte de la dimensionnalité (Ledo 2005, Martí et al. 2009, Weaver and Agarwal 2000) rend parfois possible de considérer les différentes régions avec des dimensions spatiales différentes. Par exemple, il est parfois possible d’interpréter la distribution comme une formation unidimensionnelle plus quelques hétérogénéités en 2D (ou 3D). Basée sur cette interprétation, la DAM tire profit d’une telle situation. Ainsi, l'idée principale de cette méthode est d'effectuer l'adaptativité sur la dimension spatiale en commençant par un problème de faible dimension et en utilisant les résultats obtenus pour minimiser le coût des problèmes de dimension supérieure. Nous commençons l'inversion avec un modèle 1D. Les résultats de ce problème d'inversion 1D sont utilisés comme information a priori sur les modèles de dimension supérieure. Un avantage fondamental de cette approche est que nous pouvons utiliser les solutions des problèmes de dimension inférieure précédemment calculées comme composantes du terme de régularisation associé à un problème de dimension supérieure afin d'augmenter la robustesse de l'inversion. Cette thèse propose également une analyse numérique rigoureuse de divers aspects des problèmes MT. En particulier, nous avons: (a) étudié l'effet de la source, (b) effectué une analyse fréquentielle de sensibilité, (c) illustré l'augmentation du taux de convergence lorsque l'adaptativité hp est employée, (d) séparé les effets 1D et 2D dans la solution numérique et (e) exploré l'intérêt de considérer différentes variables pour effectuer l'inversion<br>The magnetotelluric (MT) method is a passive exploration technique that aims at estimating the resistivity distribution of the Earth's subsurface, and therefore at providing an image of it. This process is divided into two different steps. The first one consists in recording the data. In a second step, recorded measurements are analyzed by employing numerical methods. This dissertation focuses in this second task. We provide a rigorous mathematical setting in the context of the Finite Element Method (FEM) that helps to understand the MT problem and its inversion process. In order to recover a map of the subsurface based on 2D MT measurements, we employ for the first time in Mts a multi-goal oriented self adaptive hp-Finite Element Method (FEM). We accurately solve both the full formulation as well as a secondary field formulation where the primary field is given by the solution of a 1D layered media. To truncate the computational domain, we design a Perfectly Matched Layer (PML) that automatically adapts to high-contrast material properties that appear within the subsurface and on the air-ground interface. For the inversion process, we develop a first step of a Dimensionally Adaptive Method (DAM) by considering the dimension of the problem as a variable in the inversion. Additionally, this dissertation supplies a rigorous numerical analysis for the forward and inverse problems. Regarding the forward modelization, we perform a frequency sensitivity analysis, we study the effect of the source, the convergence of the hp-adaptivity, or the effect of the PML in the computation of the electromagnetic fields and impedance. As far as the inversion is concerned, we study the impact of the selected variable for the inversion process, the different information that each mode provides,and the gains of the DAM approach
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Zhang, Ai Jun. "Modelling and inversion of two-dimensional magnetotelluric data." Thesis, University of Edinburgh, 1988. http://hdl.handle.net/1842/14717.
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Tzanis, Andreas. "Investigations on the properties and estimation of earth response operators from EM sounding data." Thesis, University of Edinburgh, 1987. http://hdl.handle.net/1842/11480.
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Galanopoulos, Dimitrios. "Magnetotelluric studies in geothermal areas of Greece and Kenya." Thesis, University of Edinburgh, 1989. http://hdl.handle.net/1842/10909.
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Travassos, Jandyr de Menezes. "Investigations of the analysis and modelling of magnetotelluric data." Thesis, University of Edinburgh, 1987. http://hdl.handle.net/1842/11935.
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Rydman, Oskar. "Data processing of Controlled Source Audio Magnetotelluric (CSAMT) Data." Thesis, Uppsala universitet, Geofysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-387246.
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During this project three distinct methods to improve the data processing of Controlled Source Audio Magnetotellurics (CSAMT) data are implemented and their advantages and disadvantages are discussed. The methods in question are: Detrending the time series in the time domain, instead of detrending in the frequencydomain. Implementation of a coherency test to pinpoint data segments of low quality andremove these data from the calculations. Implementing a method to detect and remove transients from the time series toreduce background noise in the frequency spectra. Both the detrending in time domain and the transient removal shows potential in improvingdata quality even if the improvements are small(both in the (1-10% range). Due totechnical limitations no coherency test was implemented. Overall the processes discussedin the report did improve the data quality and may serve as groundwork for further improvementsto come.<br>Projektet behandlar tre stycken metoder för att förbättra signalkvaliten hos Controlled Source Audio Magnetotellurics (CSAMT) data, dessa implementeras och deras för- och nackdelar diskuteras. Metoderna som hanteras är: Avlägsnandet av trender från tidsserier i tidsdomänen istället för i frekvensdomänen. Implementationen av ett koherenstest för att identifiera ”dåliga” datasegment ochavlägsna dessa från vidare beräkningar. Implementationen av en metod för att både hitta och avlägsna transienter (dataspikar) från tidsserien för att minska bakgrundsbruset i frekvensspektrat. Både avlägsnandet av trender samt transienter visar positiv inverkan på datakvaliteten,även om skillnaderna är relativt små (båda på ungefär 1-10%). På grund av begränsningarfrån mätdatan kunde inget meningsfullt koherenstest utformas. Överlag har processernasom diskuteras i rapporten förbättrat datakvaliten och kan ses som ett grundarbete förfortsatta förbättringar inom området.
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Pandey, Dhananjai Kumar. "Analysis of seismic and magnetotelluric data from Kutch, India." Thesis, University of Cambridge, 2004. https://www.repository.cam.ac.uk/handle/1810/251907.
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Shan, Chunling. "Natural and Controlled Source Magnetotelluric Data Processing and Modeling." Doctoral thesis, Uppsala universitet, Geofysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-229917.
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In this thesis, four studies using different geophysical electromagnetic methods are presented. In the first study dealing with airborne measurements, the noise response due to the rotation of the aircraft and the aircraft itself as a metallic conductive body on the Earth's electromagnetic response in very low frequency and low frequency band was investigated. The magnetic fields are independent of the aircraft in the VLF band and part of the LF band. But at higher frequencies (above 100 kHz), the signals are more influenced by the aircraft. The aircraft also generates its own noise frequencies which are mixed with the radio transmitter signals. The second and third studies are applications of radio-, controlled source-magnetotellurics and electrical resistivity tomography methods at a quick-clay landslide site in southwest Sweden. The data are processed and modeled in 2D and 3D, and the models are compared with high-resolution seismic and geotechnical data. The obtained results were further validated and refined by performing synthetic tests in the second study. The third study shows that the 3D models provide larger and more continuous volume of the quick clay structure than traditional 2D models. Both studies have shown that integrated application of geophysical methods for landslides is ideal. Quick clays often overlie the coarse-grained layers showing an increase of resistivity values in the models. In the fourth study, a new audio magnetotelluric data acquisition technique is developed and is named moving magnetotellurics (MMT). In this new technique, the magnetic sensors are placed on the ground and only 15 to 20 minutes data are acquired for each station, which usually is enough to cover the frequency range 30-300 Hz. The new technique is more efficient and convenient than the traditional magnetotelluric method, and test measurements have shown that it is an applicable method in shallow depth studies.
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Johnson, Nicholas Edward. "Magnetotelluric studies of the crust and upper mantle in a zone of active continental breakup, Afar, Ethiopia." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/7739.
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The Afar region of Ethiopia is slowly being torn apart by the Red Sea, Gulf of Aden and Main Ethiopian rifts which all meet at this remote, barren corner of Africa. Prior to rifting, volcanism probably started here some 30 million years ago, marked by the arrival of the Afar mantle plume and subsequent eruption of kilometres thick flood basalts. To the north and east the Red Sea and Gulf of Aden rifts have already progressed to become sea-floor spreading centres where new oceanic crust is produced. Active spreading on the Red Sea rift takes a landward step west into Eritrean Afar at approximately 15oN, after which divergence between the Nubian and Arabian tectonic plates is localised into 60 km long, 20 km wide magmatic segments that undergo periodic rifting cycles. This part of Afar is a unique natural laboratory where the process of transition from continental rifting to sea floor spreading can be studied. In September 2005 a dramatic rifting episode began on one such segment of the Red Sea rift in Afar (the Dabbahu magmatic segment), whereby a 60 km long dyke containing an estimated 2.5 km3 magma was intruded in just two weeks, allowing opening of up to 8 m. Since then a further 13 smaller dykes have been intruded, some with fissural eruptions of basaltic lava. Subsidence observed via geodetic observations can only account for a small fraction of the magma supply required to in ate the dykes, suggesting a deep crustal or upper mantle source must exist. The magnetotelluric (MT) method is a passive geophysical technique, used to probe the Earth to reveal subsurface conductivity. The presence of fluids can dramatically increase conductivity by orders of magnitude making the MT method ideally suited to detecting them. MT data collected from 22 sites on profiles near to and crossing the active rift are analysed and interpreted in conjunction with seismic and petrological constraints. They reveal for the first time, the existence of both a mid to lower-crustal magma chamber directly below the rift, and an o -axis zone of partial melt well within the mantle. The volume of melt contained within the crust and upper mantle below the Dabbahu segment is estimated to be at least 350 km3; enough to supply the rift at current spreading rates for almost 30 thousand years, assuming that both melt containing regions supply the rift. Vast amounts of highly conductive material, suggesting the existence of pure melt in places, are also required in the shallow crust close to Dabbahu volcano which lies at the northern end of the segment. Further data collected on the currently inactive Hararo segment which is the next one to the south of Dabbahu, show a smaller zone of partial melt that appears to be pooling at the Moho, inferred seismically to be at about 22 km, but little or no melt is required within the mid-crust. The minimum amount of melt estimated to be contained here is just 21 km3; an order of magnitude less than on the Dabbahu segment, but similar to estimates for melt within the crust found below the rift axis in the continental Main Ethiopian rift. This, along with other morphological evidence, suggests that this rift segment is less mature than the Dabbahu segment to the north, rather than it simply being at a different stage of a rifting cycle. A wide spread layer of highly conductive sediments up to 2 km thick has been imaged at most locations. This was unexpected on the Dabbahu segment where the surface of the Earth is dominated by heavily faulted basalts erupted from fissures, which are seen as a resistive uppermost layer several hundred metres thick. The high conductivity of the sediments is attributed to high heat flow and the presence of brines.
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Gill, Robert Michael. "A magnetotelluric profile across the Broken Hill and Olary Domains /." Title page, table of contents and abstract only, 2002. http://web4.library.adelaide.edu.au/theses/09SB/09sbg4756.pdf.
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Bailey, David. "Magnetotelluric studies of the Zambezi Valley mobile belt, Northern Zimbabwe." Thesis, University of Edinburgh, 1998. http://hdl.handle.net/1842/10697.
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The Mana Pools and Lower Zambezi Karoo sedimentary basins lie within the Zambezi mobile belt in northern Zimbabwe. The subsurface apparent resistivities measured at both locations are extremely low. This thesis models the resistivity structure of these two basins and the underlying material. New and pre-existing magnetotelluric data and the available seismic reflection data are used to determine the basin structure and the depth of the electrical basement. Long period magnetotelluric data were collected at 5 stations along a 60 km profile running north-south across the Mana Pools basin and onto the escarpment to the south. These data are used to augment an existing audio frequency dataset from the same area. After processing of both datasets the estimated impedance tensor is decomposed, showing that the resistivity structure of the Mana Pools basin can be modelled two dimensionally. Minimum structure models for the Mana Pools and Lower Zambezi basins are produced and compared, the latter obtained from a pre-exiting magnetotelluric dataset. There are significant differences between the structure of the two basins. The major conductive feature in the Mana Pools basin is contained within the Upper Karoo sedimentary layer and does not extend into the basement below, which is, however, of an extremely low resistivity for basement rock. The electrical basement in the Lower Zambezi basin is not detected. A good conductor is again found in the Upper Karoo sediments but extends to below 11.6 km, within the gneissic rocks of the seismic basement. The resistivity structure of the Mana Pools basin is well modelled as a series of resistive layers whose boundaries are defined by the seismic data.
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Krause, P. J. "Geomagnetic and magnetotelluric studies in the South-West of England." Thesis, University of Exeter, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.353997.
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Fleming, John B., Husna D. Hafit, Khaliza B. Khalid, et al. "Controlled Source Audio Magnetotelluric (CSAMT) Surveys in the Tucson Mountains." LASI Laboratory for Advanced Surface Imaging, The University of Arizona (Tucson, AZ), 2012. http://hdl.handle.net/10150/624629.
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Controlled Source Audio-Magnetotellurics (CSAMT) surveys were conducted in 2012 in the Tucson Mountains as a continuation of the 2010 and 2011 Laboratory for Advanced Subsurface Imaging (LASI) field studies in this area. This geologic setting was chosen for its high-resistivity impermeable volcanic layer overlaying porous sedimentary layers. This type of structure has potential for water resources and as a reservoir for compressed air energy storage (CAES). The data from 2,500 meters of CSAMT survey lines generated 900 meter-deep resistivity versus elevation cross-sections and six plan maps of the depth and elevation to the buried conductive layer. Our results are generally in agreement with the geologic cross sections developed by Lipman (1993) and previous TEM data that confirmed the presence of a deep conductive layer beneath a resistive volcanic sequence.
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Ulugergerli, Emin Ugur. "Development and application of 2D magnetotelluric inversion in complex domain." Thesis, University of Leicester, 1998. http://hdl.handle.net/2381/30430.
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The magnetotelluric method is widely used in the investigation of the geo-electric structure of the earth. The field data are traditionally inverted to reveal the subsurface structure solved using regularised iterative inversion techniques. These interpretation schemes effect matrix computations in real domain due to operational simplicity. The speed of convergence of these techniques is controlled by the calculation type and the size of the program or more specifically, size of the matrices used. A common problem encountered when dealing with real matrices in 2D regularised inversion is their huge size. To partly overcome this problem, a new inversion strategy using complex singular value decomposition techniques has been successfully developed. The use of analytical partial derivatives and a variety of problem regularization measures ensure that the scheme is stable and rapidly convergent. In this method, instead of using the Cagniard apparent resistivity and phase, the frequency normalised impedance is adopted as the interpretative data functions for improved model resolution. Sample applications to several synthetic and to field data from Parnaiba Basin in Brazil proved successful and are presented in this thesis. It is also found that the complex form of the data-space and parameter-space eigenvectors contain information on parameter resolution. Suggestions are made for further studies especially of methods of improving parameter resolution in 2D inversion.
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Adetunji, Ademola Quadri. "Resistivity structure of the Precambrian Grenville Province, Canada." Tectonophysics, 2014. http://hdl.handle.net/1993/23450.
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As part of the southern Ontario POLARIS project, this thesis uses magnetotelluric methods to investigate the lithospheric architecture of the Proterozoic Grenville Province and its margin with the Archean Superior Province. The first multi-dimensional crustal and lithospheric resistivity images for this region are presented.
The resistivity structure of the Phanerozoic sedimentary rocks in the lower Great Lakes region was determined using 1-D methods. The responses are strongly affected by a 20-23 S conductive layer within the sedimentary rocks, interpreted to be associated with Upper Ordovician shale units. This layer excludes resolution of resistivity structure of underlying crust.
The resistivity structure of the Precambrian crust and lithosphere was determined using 2-D methods. Different strike azimuths were determined for the crust, the upper lithospheric mantle and the deeper mantle layer. The crustal resistivity model for a profile from 50oN79oW to 43oN76oW images resistive Laurentian margin rocks dipping southeast to the base of the crust, bounded by the Grenville Front and the Central Metasedimentary Belt Boundary Zone. In a 2-D model of the mantle lithosphere for the same profile, a conductor at 70-150 km depth, located along-strike from the Mesozoic Kirkland Lake and Cobalt kimberlite fields, is interpreted to be due to mantle re-fertilization. Results from multiple MT profiles indicate conductive (<10 Ω.m) lithospheric mantle beneath the Central Metasedimentary Belt and show that the northwestern Grenville Province is characterized by large-scale, resistive lithosphere (>10,000 Ω.m) extending for about 300 km beneath the Grenville Province and 800 km along strike. Lithospheric thickness is interpreted to be 280 km; local decreases in this depth are attributed to refertilization of the lower mantle lithosphere by fluids associated with Cretaceous kimberlite magmatism.
Anisotropic 2-D modeling reveals minimal electrical anisotropy (<10%) at mantle depths in contrast to the factor of 15 anisotropy determined in earlier 1-D studies. This result suggests that observed MT response anisotropy is caused by large-scale structures. Strike direction in the upper lithospheric mantle is interpreted to be related to the Archean fabric of the Superior craton and in the deeper, conductive, mantle it is interpreted to have been established in the Cretaceous.
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Niasari, Sintia W. [Verfasser]. "Magnetotelluric Investigation of the Sipoholon Geothermal Field, Indonesia / Sintia W. Niasari." Berlin : Freie Universität Berlin, 2015. http://d-nb.info/1065670249/34.
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Chen, Jin [Verfasser]. "Using Empirical Mode Decomposition to Process Marine Magnetotelluric Data / Jin Chen." Kiel : Universitätsbibliothek Kiel, 2014. http://d-nb.info/1049189329/34.
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Ogaya, Garcia Xènia. "Magnetotelluric characterisation and monitoring of the Hontomín CO2 storage site, Spain." Doctoral thesis, Universitat de Barcelona, 2014. http://hdl.handle.net/10803/284957.
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The electromagnetic methods are especially interesting for the characterisation and monitoring of geological storage of CO2 sites. The electrical resistivity is a physical parameter that depends on the mineralogical composition of the rocks, as well as on other characteristics such as porosity, pore connectivity, pore fluid salinity, saturation, temperature and pressure. The CO2 injected in the reservoir produce changes in the resistivity that enables its detection with electromagnetic methods.
However, it is necessary to have a thorough knowledge of the structure at the pre-injection state to detect and quantify the changes produced by the injected CO2. The magnetotelluric method is the only electromagnetic method with a penetration depth ranging from ten of metres to hundreds of kilometres depth. Furthermore, this method allows determining the directionality and evolution of the structures in depth thanks to its tensorial character.
Hence, the objective of this thesis is to characterise using the magnetotelluric method, the Technological Development Plant (TDP) of Hontomín for Geological Storage of CO2 in a deep saline formation and evaluate the capabilities of the magnetotelluric method to monitor the injected gas.
The work presented in this thesis represents an important contribution to the characterisation projects of CO2 storage sites in deep saline formations. The 3D resistivity model obtained defines the reference geoelectrical model for the subsequent electromagnetic monitoring studies. Moreover, the model shows the dome structure of Hontomín and the main fault system. The model allows identifying the potential leakage zones and defines the monitoring needs for the Hontomín TDP. This model also correlates satisfactorily with hydrogeochemical, seismic, gravimetric and well-log data. Additionally, the monitoring capabilities of the magnetotelluric method have been assessed in this work, proposing a new methodology to improve the resolution of the surface magnetotelluric responses to resistivity changes occurred at the reservoir level.<br>La captura y almacenamiento geológico de dióxido de carbono (CO2) constituye una de las soluciones tecnológicas propuestas en la actualidad para reducir las emisiones de este gas a la atmosfera. El objetivo de esta tecnología es capturar y transportar el gas desde los grandes focos emisores hasta los lugares seleccionados como almacenes geológicos, donde es inyectado. Esta tesis se centra en la Planta de Desarrollo Tecnológico (PDT) de Hontomín (España), donde el almacenamiento geológico se llevará a cabo en un acuífero salino profundo. La PDT se enmarca en el proyecto Compostilla OXYCFB300, dentro del Programa Energético Europeo para la Recuperación (European Energy Programme for Recovery).
La mayoría de las propiedades físicas de la roca almacén, en especial la resistividad eléctrica, variarán tras la inyección de CO2. El fluido salino conductor contenido en el poro será sustituido por el gas, de carácter más resistivo, reduciendo el volumen de agua disponible para la conducción iónica. Por ello, los métodos electromagnéticos, sensibles a la resistividad eléctrica, son especialmente interesantes para este tipo de proyectos ya que permiten estudiar la evolución del gas inyectado y estimar la saturación de CO2 en el poro.
Esta tesis tiene por objetivo la caracterización, control y seguimiento de la PDT de Hontomín mediante el método magnetotelúrico. El objetivo principal es la obtención de un modelo geoeléctrico tridimensional (3D) de referencia, que permita caracterizar la zona en la situación de preinyección y sirva de modelo base para los posteriores estudios de seguimiento con métodos electromagnéticos de fuente controlada. Asimismo, esta tesis persigue evaluar la capacidad de control y seguimiento del método magnetotelúrico. Con este propósito, se ha desarrollado una nueva metodología para mejorar la resolución de las respuestas magnetotelúricas superficiales a cambios de resistividad producidos en el reservorio (metodología denominada layer stripping).
La caracterización de la PDT de Hontomín se ha llevado a cabo en dos etapas. En la primera etapa se adquirió un perfil magnetotelúrico de orientación NS. Este primer estudio demostró la idoneidad del método para caracterizar la zona de estudio y proporcionó un modelo geoeléctrico bidimensional (2D) de la misma. En la segunda etapa se completó la adquisición de los datos, lo que permitió la obtención del modelo geoeléctrico 3D de la PDT. Esta tesis presenta ambos estudios de caracterización. Cada uno de ellos es justificado por un análisis previo de dimensionalidad de los datos y detalla la metodología de inversión empleada para alcanzar resultados válidos y apropiados.
El modelo 2D obtenido previamente ha sido validado por el modelo 3D, el cual se correlaciona satisfactoriamente con datos hidrogeoquímicos, sísmicos, gravimétricos y datos de pozos, entre otros. Este modelo 3D constituye el modelo geoeléctrico de referencia de la PDT, siendo la principal contribución de esta tesis. El modelo muestra la estructura de domo de Hontomín y los principales conjuntos de fallas. Permite así identificar las posibles zonas de fuga y definir las necesidades de control y seguimiento de la PDT.
De este modo, esta tesis supone una importante contribución a los proyectos de caracterización de almacenes de CO2 en acuíferos salinos profundos. El método magnetotelúrico ha demostrado ser una técnica electromagnética apropiada para caracterizar el área de estudio. Los resultados obtenidos son significativos y ponen de manifiesto la importancia de establecer un modelo geoeléctrico de la situación de preinyección a fin de caracterizar la estructura, concretar las necesidades de control de la planta y definir el modelo de referencia para los posteriores estudios de seguimiento. Los estudios electromagnéticos son complementarios a estudios de caracterización sísmicos y dada su sensibilidad a la conductividad eléctrica, se establecen como métodos de resolución superior para determinados aspectos de interés en el almacenamiento de CO2 y su seguimiento a largo plazo.
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Li, Shenghui. "The indepth magnetotelluric experiment on the Tibetan Plateau and its implications /." Thesis, Connect to this title online; UW restricted, 2001. http://hdl.handle.net/1773/6817.
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Valtersson, Einar. "Comparison of data analysis methods KMSProTF and MsDEMPCA using Magnetotelluric data." Thesis, Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-80195.
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In this work two ways of processing controlled-source magnetotelluric (MT) data were tried and compared against each other. The aim was to evaluate the differences between a multivariate-based processing method to a bivariate processing method. The software KMSProTF represents conventional processing using bivariate and robust statistics. MsDEMPCA utilizes a multi-variate Criss-Cross regression scheme to improve the condition of the data-matrix before robustly decomposing it into principal components. Data from the FENICS-19 survey in northern Scandinavia was processed to transfer functions (TF) using the respective method. The TFs were visually interpreted in KMSProTF. There were no significant differences found between the methods. In addition a calibration between instruments was carried out, which caused an exclusion of parts of the data-set.
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Parr, Ronald S. "Development of magnetotelluric processing and modelling procedures : application to Northern England." Thesis, University of Edinburgh, 1991. http://hdl.handle.net/1842/12772.
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The magnetotelluric (MT) method is a geophysical technique which uses observations of the naturally occurring electromagnetic (EM) field variations to determine the electrical impedance as a function of frequency. Owing to the variable signal and often high level of noise contamination, it is usual to collect large numbers of observations and perform parameter regression in order to gain reliable estimates of this Earth response function. It is then transformed into more interpretable, albeit non-unique, resistivity versus depth models. In the course of this study, the processing, modelling and interpretation of MT observations from Northern England are considered. This includes previously unpublished data as well as a re-examination of spatially more extensive measurements which were acquired during earlier investigations. Existing MT field equipment has been adapted to allow local and remote reference observations to be collected and the results show that the amplitude of the impedance is contaminated by a lower level of noise induced bias. In addition, the resolution of the resulting model of the near structure can be enhanced by supplementary D.C. resistivity measurements. Considerable attention is focused on the development of new methods for processing and modelling MT observations. In particular, the background theory and implementation of a robust and constrained method for the estimation of the impedance is described in some detail. This method is demonstrated on real and synthetic unreferenced observations and shown to improve the consistency and the reliability of the resulting response function by reducing the level of noise contamination. One dimensional models are obtained for 42 MT response functions from Northern England. These are computed using a new 'exploratory' parametric technique which not only aims to find the best fitting model, but also to investigate its range of uniqueness. Additional, more interpretative modelling methods are also developed to improve the consistency of the models from adjacent sites. An experimental procedure which uses the constraining information provided by 2-D gravity model sections is also considered. At a subset of the sites over the Alston Block and the southern margin of the Northumberland Trough a strictly 2-D MT model is derived.
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Hill, Edmund Roger Gerard. "A magnetotelluric study in the Moine Thrust region of northern Scotland." Thesis, University of Edinburgh, 1987. http://hdl.handle.net/1842/14067.
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Zhang, Yuanhua. "Wavelet transforms, neural networks and migration applied to magnetotellurics." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq23897.pdf.
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Dosso, Stanley Edward. "Inversion and appraisal for the one-dimensional magnetotellurics problem." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/30692.
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The method of magnetotellurics (MT) uses surface measurements of naturally-occurring electromagnetic fields to investigate the conductivity distribution within the Earth. In many interpretations it is adequate to represent the conductivity structure by a one-dimensional (1-D) model. Inferring information about this model from surface field measurements is a non-linear inverse problem. In this thesis, linearized construction and appraisal algorithms are developed for the 1-D MT inverse problem.
To formulate a linearized approach, the forward operator is expanded in a generalized Taylor series and second-order terms are neglected. The resulting linear problem may be solved using techniques of linear inverse theory. Since higher-order terms are neglected, the linear problem is only approximate, and this process is repeated iteratively until an acceptable model is achieved. Linearized methods have the advantage that, with an appropriate transformation, a solution may be found which minimizes a particular functional of the model known as a model norm. By explicitly minimizing the model norm at each iteration, it is hypothesized that the final constructed model represents the global minimum of this functional; however, in practice, it is difficult to verify that a global (rather than local) minimum has been found.
The linearization of the MT problem is considered in detail in this thesis by deriving complete expansions in terms of Fréchet differential series for several choices of response functional, and verifying that the responses are indeed Fréchet differentiable. The relative linearity of these responses is quantified by examining the ratio of non-linear to linear terms in order to determine the best choice for a linearized approach. In addition, the similitude equation for MT is considered as an alternative formulation to linearization and found to be inadequate in that it implicitly neglects first-order terms.
Appropriate choices of the model norm allow linearized inversion algorithms to be formulated
which minimize a measure of the model structure or of the deviation from a (known) base model. These inversions construct the minimum-structure and smallest-deviatoric model, respectively. In addition, minimizing I₂ model norms lead to smooth solutions which represent structure in terms of continuous gradients, whereas minimizing I₁ norms yield layered conductivity models with structural variations occurring discontinuously. These two formulations offer complementary representations of the Earth, and in practice, a complete interpretation should consider both. The algorithms developed here consider the model to be either conductivity or log conductivity, include an arbitrary weighting function in the model norm, and fit the data to a specified level of misfit: this provides considerable flexibility in constructing 1-D models from MT responses.
Linearized inversions may also be formulated to construct extremal models which minimize or maximize localized conductivity averages of the model. These extremal models provide bounds for the average conductivity over the region of interest, and thus may be used to appraise model features. An efficient, robust appraisal algorithm has been developed using linear programming to extremize the conductivity averages. For optimal results, the extremal models must be geophysically reasonable, and bounding the total variation in order to limit unrealistic structure is an important constraint.
Since the extremal models are constructed via linearized inversion, the possibility always exists that the computed bounds represent local rather than global extrema. In order to corroborate the results, extremal models are also computed using simulated annealing optimization. Simulated annealing makes no approximations and is well known for its inherent ability to avoid unfavourable local minima. Although the method is considerably slower than linearized analysis, it represents a general and interesting new appraisal technique.
The construction and appraisal methods developed here are illustrated using synthetic test cases and MT field data collected as part of the LITHOPROBE project. In addition, the model construction techniques are used to analyze MT responses measured at a number of sites on
Vancouver Island, Canada, to investigate the monitoring of local changes in conductivity as a precursor for earthquakes. MT responses measured at the same site over a period of four years are analyzed and indicate no significant changes in the conductivity (no earthquakes of magnitude greater than 3.0 occurred in this period). Conductivity profiles at a number of sites are also considered in an attempt to infer the regional structure.
Finally, a method of correcting linearized inversions is developed. The corrections consist of successively approximating an analytic expression for the linearization error. The method would seem to represent a novel and practical approach that can significantly reduce the number of linearized iterations. In addition, a correspondence between the correction steps and iterations of the modified Newton's method for operators is established.<br>Science, Faculty of<br>Earth, Ocean and Atmospheric Sciences, Department of<br>Graduate
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Yan, Ping. "Inversion of Magnetotelluric Data Constrained by Borehole Logs and Reflection Seismic Sections." Doctoral thesis, Uppsala universitet, Geofysik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-303498.
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This thesis presents two new algorithms for doing constrained Magnetotelluric (MT) inversion based on an existing Occam 2D inversion program. The first algorithm includes borehole resistivity logs as prior information to constrain resistivity directly in the vicinity of boreholes. The second algorithm uses reflection seismic data as prior constraints to transfer structural information from seismic images to 2D resistivity models. These two algorithms are efficient (proved through tests of synthetic examples) and widely applicable. In this thesis, they have been successfully applied to the COSC (Collisional Orogeny in the Scandinavian Caledonides) MT data. The COSC project aims to study the mountain belt dynamics in central Sweden by drilling two 2.5 km deep boreholes. MT data were collected to locate the main décollement that separates the overlying Caledonian allochthons and the underlying Precambrian basement, as the main décollement is associated with very conductive Alum shale. The previous interpretation based on part of the COSC seismic profile (CSP) was that the main décollement was located along a reflection with depth of 4.5 km underneath Åre and ~3 km underneath Mörsil, in central Jämtland. The MT resistivity model reveals a very conductive layer in the central and western parts of the profile, the top of which coincides with the first seismic reflection. This means that the first conductive alum shale layer occurs at less than 1 km depth, supporting a new interpretation of the main décollement at shallower depth. In a re-interpretation of the CSP data based on the MT model, the main décollement occurs a few hundred metres below the top of the conductor and is coincident with a laterally continuous seismic reflection. Further, the overlying seismic reflections resemble imbricated alum shale of the Lower Allochthon. MT inversion using seismic constraints from CSP gives further support to the new interpretation. Moreover, MT investigations were conducted in the Alnö alkaline and carbonatite ring-intrusion complex in Sweden. 2D and 3D resistivity models inverted from MT data together with resistivity and porosity laboratory measurements delineate a fossil magma chamber as a resistive anomaly surrounded by electrically conductive up-doming and ring-shaped faults and fractures.
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Aradiy, Edy Muhammad. "RESISTIVITY STRUCTURE BENEATH SAKURAJIMA AND MERAPI VOLCANOES INFERRED FROM MAGNETOTELLURIC(MT) SURVEY." 京都大学 (Kyoto University), 1995. http://hdl.handle.net/2433/160890.
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本文データは平成22年度国立国会図書館の学位論文(博士)のデジタル化実施により作成された画像ファイルを基にpdf変換したものである<br>Kyoto University (京都大学)<br>0048<br>新制・論文博士<br>博士(理学)<br>乙第8756号<br>論理博第1260号<br>新制||理||888(附属図書館)<br>UT51-95-B221<br>(主査)教授 西村 進, 教授 小林 芳正, 教授 坂野 昇平<br>学位規則第4条第2項該当
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Sakkas, Vassilis A. "Combined transient electromagnetic and magnetotelluric study of the southern Kenya Rift Valley." Thesis, University of Leicester, 1999. http://hdl.handle.net/2381/30437.
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The transient electromagnetic (TEM) method and the magnetotelluric (MT) technique have been applied to determine the electrical resistivity structure across the southern Kenya Rift Valley. The main profile extends from the shores of Lake Victoria, west of the Rift Valley, to the north of the Chyulu Hills volcanic chain, 150 km SE of the rift. A second profile runs parallel to the Chyulu Hills volcanic trend. Data from 19 stations along the two profiles have been processed using classical techniques and in the case of MT, analysed with modern tensor decomposition methods. The TEM data have facilitated the removal of static shift effects from the MT data and recovery of the near-surface (<300 m) geoelectric structure. One-dimensional joint inversion of TEM and MT data yielded an approximate geoelectric structure for the region. Subsequent two-dimensional modelling has revealed a more realistic resistivity distribution for the complex environment of the Kenya Rift. A resistive (>2000 .m) Archaean crust 30 km thick, with a 10-12 km mid-crustal conductive (100 .m) zone, resting on a moderately resistive (100 .m) mantle appears at the west end of the main profile. A conductive fault-like zone extending to mantle depths in the area of the Oloololo Escarpment coincides with the exposed boundary between the Archaean Nyanza Craton and the Proterozoic Mozambique Belt. A poorly constrained highly resistive (>10000 .m) (Proterozoic ?) crust is found at the western flank of the rift. Low resistivities (<50 .m) are found down to the base of the crust in the rift zone and are possibly due to the presence of sedimentary fill deposits at shallow depths, and the presence of magmatism and partial melt at deeper levels. East of the rift a less sharply defined geoelectric margin, offset from the accepted topographic and geologic boundary of the rift, marks the transition to a more resistive (1000 .m.) Proterozoic crust. Significantly enhanced conductivities (<100 .m) are implied in the complex 3-D region of the Chyulu Hills.
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Mohamed, Adel K. "Applications of magnetotelluric and transient electromagnetic methods in groundwater and engineering studies." Thesis, University of Leicester, 2002. http://hdl.handle.net/2381/30449.
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The main aim of this study is to use the transient electromagnetic (TEM) and magnetotelluric (MT) methods to determine the electrical resistivity distribution of the subsurface and locate possible structural features controlling groundwater distribution in the northern and south-eastern margins of Parnaiba basin, Brazil. MT data from 24 stations along two profiles across the margins of the basin have been processed using standard tensorial techniques to obtain the interpretable response functions. The TEM data recorded at the same sites facilitated the removal of static shift and the recovery of the near-surface structure. One-dimensional (1-D) joint inversion of TEM and MT data yielded an approximate geoelectric structure for each profile. Subsequent two-dimensional (2-D) modelling revealed a more realistic resistivity distribution for each profile. The result of 2-D regularized inversion of MT data delineated the main sedimentary sequences and deep basement features. A resistive crystalline basement (≥ 200 &OHgr;m) is overlain by relatively conductive sedimentary sequences of varying resistivities and thicknesses. The existence of a major basement trough at the expected position of a concealed fault in the north-eastern margin of the basin was proved by the MT model. This anomalous zone is interpreted to have a thick development of granular sediments and may be a good site for groundwater development. The 2-D model for the south-eastern profile defined the position of a major fault, which is interpreted as Picos fault and may have implication for groundwater development. A graben-like structure is also suggested ∼10 km further east from Picos fault and considered to be a good target for groundwater development. Overall, the 2-D MT inversion results are consistent with the available geological information and offer new insights into the deep structure of the basin margins of Parnaiba basin.
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Hjärtén, Martin. "Master thesis in interpretation of controlled-source radiomagnetotelluric data from Hallandsåsen." Thesis, Uppsala University, Geophysics, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8015.
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<p>Controlled Source Tensor Magnetotelluric (CSTMT) ground measurements were executed on the Hallandsåsen horst where a major tunnel is under construction. The instrument system EnviroMT are used for this purpose. The major research aspect of this thesis has been to form an opinion of the effectiveness of the method by comparing the results from the CSTMT survey with a prior investigation performed with the DC resistivity method. Another important part of this thesis has been to compile the basic and fundamental CSTMT and RMT theory, in a way that people outside the EM community easily can be introduced to the subject.</p><p>When comparing the different inversion models from the CSTMT and DC resistivity surveys one can see differences in the depth at which the conductors are resolved. In the CSTMT inversion models (TE+TM) there are two conductors that possibly can reach the depth of the tunnel in construction. These conductors are not resolved at the deeper structures in the DC resistivity models. Whether the conductors in the CSTMT inversions (TE+TM) truly extend to the depth at which they are modeled, or if they in deeper parts are artificial effects of regularisation in the inversion cannot be said for sure. Accounting for the low frequencies utilised in the TE mode, one has very strong arguments that the deep conductors seen in the CSTMT model are true.</p><p>The TE-mode models have shown to be much less affected by the complex problems of near field effects in comparison with the TM-mode models. The evidence of the near field effects is very prominent in the TM-mode phase, but in the phase of the TE-mode one can not see any such tendencies. However, one can see a discontinuity in the same part of three profile lines which shows that the data is disturbed but not nearly as much as in the TM-mode. The apparent resistivity seems to be over all less affected by the near field effects. In the apparent resistivity of the TE-mode, one can not discern any near field effects at all.</p><p>In the TM-mode, the apparent resistivity shows higher apparent resistivity than the real apparent resistivity in the near field. To receive more information about the deeper structures, lower controlled source frequencies were allowed in the TE-mode than in the TM-mode inversion models. The RMS in the TE-mode inversions has not been deteriorated, which is an another indication that the TE mode is not very disturbed by the near field effects.</p><p>The RMT inversion models are shown to be heavily biased in the deeper parts to which the RMT data are insensitive and regularization determining the outcome of the inversion. One can also see that regularisation is influencing the whole inversion model. In the shallow subsurface the inversion models should be same for CSTMT and RMT, but one can see differences in resistivity between the models.</p><p>The real induction arrows show features that are not as clearly displayed in either the phase or apparent resistivity. It seems that the real induction arrows are better at detecting lateral differences in conductivity in a more resistive media, than the phase and apparent resistivity.</p>
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Ismail, Nazli. "Controlled Source Radiomagnetotelluric (CSRMT) Applications in Environmental and Resource Exploration." Doctoral thesis, Uppsala universitet, Geofysik, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-102750.
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An integrated use of radio magnetotelluric (RMT) and controlled source tensor magnetotelluric (CSTMT) measurements, the so-called CSRMT method, has been employed in environmental and resource exploration studies. A number of case histories, including a groundwater investigation in glacial deposits, a study of fracture zones for geotechnical purposes and a mining exploration study of a copper deposit, are presented in this thesis in order to illustrate the usefulness and capability of the CSRMT method. The resolutions of the estimated models using various types of data are studied. Magnetotelluric transfer functions are used to analyze the dimensionality, the near surface resistivity distortions and the near field effects in the case of CSTMT data analysis. The near field effects in CSTMT data have also been identified by performing 2½D forward modelling. Data analysis, dimensionality tests and forward modelling show that at the lowest frequencies used the CSTMT transfer functions are generally distorted by source effects, except when the source-receiver distances are sufficient large compared with the penetration depth. Regarding CSTMT transfer functions, apparent resistivities are generally less distorted than phases. TM mode transfer functions are more affected by the sources than TE mode, while tipper vectors generally contain source signatures at all frequencies. Based on the analysis of dimensionality and source effects 2D inverse modelling of CSTMT and RMT data, as well as their combination, have been performed under the plane wave assumption. The RMT method proved to be a powerful tool for imaging the upper 50 m near-surface, but their penetration depth reduces as a conductive layer structures cover the targets at depth. The penetration depth can be increased by including the CSTMT data in the modelling if the measurements are in the far field range. The resolution of the deeper parts of the models may be improved by performing a joint inversion of TE and TM modes, if the strike direction is well-defined. Alternatively, inversion of determinant data can be performed, since the determinant data are less affected by 3D structures and source effects. However the resolution of the determinant models is somewhat degraded compared to the models inverted from combined TE and TM modes.
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Chen, Xiaoming [Verfasser], and Ute [Akademischer Betreuer] Weckmann. "Two-dimensional constrained anisotropic inversion of magnetotelluric data / Xiaoming Chen. Betreuer: Ute Weckmann." Potsdam : Universitätsbibliothek der Universität Potsdam, 2012. http://d-nb.info/1029243824/34.
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