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Airborne VLF measurements and mapping of ground conductivity in Sweden |
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| Authors: | Laust B Pedersen Lena Persson Mehrdad Bastani Sören Byström |
| Institution: | 1. VIRG-Rudgeofizika, Petrogradskaya nab. 18, korp. 3V, St. Petersburg, 197046, Russia;2. Institute of Earth Sciences, St. Petersburg State University, per. Dekabristov 16, St. Petersburg, 199155, Russia;1. Department of Earth Resources Engineering, Kyushu University, Fukuoka 819-0395, Japan;2. Exploration Geophysics and Mining Engineering Department, Korea Institute of Geoscience and Mineral Resources, Daejeon 305-350, Republic of Korea;1. Department of Earth Science, Sultan Qaboos University, Muscat, Post Box: 36, Postal Code 123, Oman;2. Atomic Minerals Directorate for Exploration and Research, Hyderabad-500 016, India |
| Abstract: | Airborne VLF data are routinely collected by The Geological Survey of Sweden (SGU) as part of its bedrock mapping programme. In this paper we demonstrate that the novel Tensor VLF technique developed at Uppsala University and SGU can provide useful qualitative and quantitative information about the electrical conductivity distribution in the upper few hundred meters. Single transmitter scalar VLF maps emphasize those conductive structures that have dominant strikes in the direction of the transmitter. The tensor tipper (essentially the vertical magnetic field from currents along the strike direction) calculated from multiple transmitters is dependent only upon the underlying conductivity structure. Transformation of the tipper into the peaker (the horizontal divergence) has proven to enhance the lateral resolution while the transformation to the apparent resistivity can be used to discriminate different rock types. Two case histories from the application of VLF data are presented in this study. Two dimensional structures can be quantitatively modelled by modern inversion methods developed originally for deep electromagnetic MT soundings. Direct inversion of the real and imaginary parts of the tipper provides more quantitative information about the subsurface resistivity distribution. |
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