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Airborne VLF measurements and variations of ground conductivity: a tutorial
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences.
In: Surveys in GeophysicsArticle in journal (Refereed) Submitted
URN: urn:nbn:se:uu:diva-91558OAI: oai:DiVA.org:uu-91558DiVA: diva2:164331
Available from: 2004-03-31 Created: 2004-03-31Bibliographically approved
In thesis
1. A Broad View on the Interpretation of Electromagnetic Data (VLF, RMT, MT, CSTMT)
Open this publication in new window or tab >>A Broad View on the Interpretation of Electromagnetic Data (VLF, RMT, MT, CSTMT)
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
En bred syn på Tolkning av Elektromagnetiska Data (VLF, RMT, MT, CSTMT)
Abstract [en]

The resolution power of single Very Low Frequency (VLF) data and multi-frequency Radiomagnetotelluric (RMT) data in delineating conductive structures typical for the sedimentary cover and crystalline basement in Scandinavia is studied with a view to future developments of the technique to increasing the frequency range into the LW radio band. Airborne and ground VLF data are interpreted and correlated with RMT measurements made on the ground to better understand the resolution power of VLF data. To aid in this understanding single and multifrequency VLF and RMT responses for some typical resistivity structures are analyzed. An analytic model is presented for obtaining unique transfer functions from measurements of the electromagnetic components on board an air-plane or on the ground. Examples of 2D inversion of ground and airborne VLF profiles in Sweden are shown to demonstrate the quantitative interpretation of VLF data in terms of both lateral and depth changes of the resistivity in the uppermost crust.

Geothermal resources are ideal targets for Electromagnetic (EM) methods since they produce strong variations in underground electrical resistivity. Modelling of Magnetotelluric (MT) data in SW Iceland indicates an alteration zone beneath the surface, where there are no obvious geothermal manifestations, in between Hengill and Brennisteinsfjoll geothermal systems. It suggests that a hydrothermal fluid circulation exists at depth. It also proves that the MT method, with its ability to map deep conductive features can play a valuable role in the reconnaissance of deep geothermal systems in active rift regimes such as in Iceland.

A damped nonlinear least-squares inversion approach is employed to invert Controlled Source Tensor MT (CSTMT) data for azimuthal anisotropy in a 1D layered earth. Impedance and tipper data are inverted jointly. The effects of near-surface inhomogeneities are parameterized in addition to each layer parameter(s). Application of the inversion algorithm to both synthetic and field data shows that the CSTMT method can be used to detect azimuthal anisotropy under realistic conditions with near surface lateral heterogeneities.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2004. 68 p.
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 959
Geophysics, Airborne, azimuthal anisotropy, CSTMT, distortion, EM, geothermal, Hengill, mineralization, MT, peaker, resolution, RMT, tipper, tensor VLF, VLF, Geofysik
National Category
urn:nbn:se:uu:diva-4146 (URN)91-554-5925-0 (ISBN)
Public defence
2004-04-29, Axel Hambergsalen, Geocentrum, Villavägen 16, SE-752 36, Uppsala, 10:00
Available from: 2004-03-31 Created: 2004-03-31 Last updated: 2016-05-13Bibliographically approved

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