<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>

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. 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. 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. 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. 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. 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.

Thesis (doctoral)--Rheinische Friedrich-Wilhelms-Universität zu Bonn, 1983. / Bibliography: p. 98-103.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1974. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND LINDGREN / Vita. / Bibliography: leaves 195-203. / Ph.D.

In this work the magnetic and magnetotelluric (MT) geophysical methods have been used to produce two 3D models for the Laver area in southern Norrbotten. A new discovery of a porphyry copper deposit located at the Lill-Laverberget was reported by Boliden in 2012. The goal with the models is to form a better understanding of the setting for the porphyry deposit and to see if any of the geophysical methods are suited to be used in exploration for it. For starters an edge detector (Beiki, 2010) was used on magnetic data to identify structures and petrological contacts in the area. The magnetic data was modelled using the SimPEG (Cocket, et al., 2015) inversion software to create a 3D model over the area. The Magnetic method quite clearly managed to resolve the volcanic units in the Laver area. MT data was collected during fieldwork in September of 2018 and modelled using the MOD3DEM (Egbert &amp; Kelbert, 2012) inversion software. The MT model did not show any clear anomalies that could be related to the deposit. / I detta arbete så har de magnetiska och magnetotelluriska (MT) geofysiska metoderna används för att skapa två 3D modeller över Laverområdet i södra Norrbotten. I området finns en porfyrkopparfyndighet som Boliden rapporterade in 2012. Målet med båda modellerna är att fördjupa förståelsen för bildningsmiljön för fyndigheten och för att se hur lämpade de geofysiska metoderna är för prospektering. Det första steget var att använda befintliga magnetiska data och processa den med ED funktionen (Beiki, 2010) för att identifiera strukturer och bergartskontakter i området. Den magnetiska data användes för att producera en 3D modell med inversionsprogrammet SimPEG (Cocket, et al., 2015). Denna modell kunde skilja mellan vulkaniska och övriga bergarter i området. Magnetotelluriska data samlades in i september 2018 och modellerades med MOD3DEM (Egbert &amp; Kelbert, 2012), denna modell hade dock problem att finna anomalier i området.

Graduation date: 2000

Falkenberg area is located in southwest Sweden formed in the Sveconorwegian orogen and contains an extremely complex geological structure. Multiple geophysical datasets have been acquired and together with available petrophysical information, models corresponding to the subsurface geological structures were generated. The collected data comprise ground magnetic, AMT (Audio Magnetotelluric) and RMT (Radio Magnetotelluric) data. The available airborne magnetic and ground gravity data acquired by the Geological Survey of Sweden (SGU) as well as the reflection seismic section from a study made by Uppsala University further aids in obtaining substantially improved interpretation of the geometry of the structures along the AMT profile. The principal objective of this profile was to delineate and map the possible deformation zone crossed by the profile. The AMT study was expected to complement existing geophysical data and improve existing interpretations. The Ullared deformation zone contains decompressed eclogite facies rocks. The presented results were obtained by comparison of different geophysical methods along the profile. The susceptibility model and resistivity model show that eclogites have higher resistivity and susceptibility than the surrounding structures. However use of the Occam type of inversion on the AMT data, makes the resistivity model smoother than the susceptibility model and as a results it is difficult to estimate the dip of the structures. The AMT profile and the seismic section show the same dip direction (NE) for the eclogite bearing structures although due to the smoothing in the AMT model the dips seen in the seismic section cannot be recovered in the resistivity model.

Thesis (M. Sc.), Memorial University of Newfoundland, 1998. / Bibliography: leaves 187-201. Also available online.

Thesis (Ph. D.)--Missouri University of Science and Technology, 2010. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed June 30, 2010) Includes bibliographical references (p. 129-135).

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Science, 1979. / Microfiche copy available in Archives and Science. / Vita. / Bibliography: leaf 41. / by Robert Alvin Davis. / M.S.