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2D joint inversion of RMT and ERT data versus individual 3D inversion of full tensor RMT data: An example from the Trecate site in Italy
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences. Geological Survey of Sweden.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
Institute of Geophysics, Department of Earth Sciences, ETH Zurich.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
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2012 (English)In: Geophysics, ISSN 0016-8033, E-ISSN 1942-2156, Vol. 77, no 4, WB233-WB243 p.Article in journal (Refereed) Published
Abstract [en]

Tensor radiomagnetotelluric (RMT) and electrical resistivity tomography (ERT) data were acquired along 10 parallel lines to image electrical resistivity of the vadose and the saturated zone in an area near Trecate, 45 km west of Milan in Italy. In 1994, the area was exposed to an oil contamination caused by a tank explosion and has since been subject to monitoring and remediation programs. For the first time, we have examined a 3D inversion of full tensor RMT data and have compared the results with 2D joint inversion of RMT and ERT data. First, a synthetic 3D resistivity model with similar variations close to those measured at the Trecate site was generated for the comparison. The synthetic tests showed that resistivity models from 2D joint inversion of ERT and RMT data contain more details closer to the surface compared to the models from the 3D inversion of tensor RMT data. High resistivity structures are better resolved by the 2D joint inversion, whereas the more conductive features are better recovered by the 3D inversion. In the next step, the ERT and RMT data collected in the Trecate site were modeled with the same approaches used in the synthetic modeling. Using the measured tensor RMT data, it was possible to carry out full 3D inversion to study the underlying geology. Comparison between the resistivity models from both inversions with the lithological data from the existing boreholes, resistivity models from the inversion of crosshole resistivity data, and water content models from magnetic resonance soundings measurements showed that the electrical resistivity, depth to the top and thickness of the water saturated zone is modeled more accurately With the 3D inversion.

Place, publisher, year, edition, pages
2012. Vol. 77, no 4, WB233-WB243 p.
National Category
Geophysics
Research subject
Geophysics with specialization in Solid Earth Physics
Identifiers
URN: urn:nbn:se:uu:diva-165142DOI: 10.1190/GEO2011-0525.1ISI: 000307799500022OAI: oai:DiVA.org:uu-165142DiVA: diva2:472006
Available from: 2012-01-03 Created: 2012-01-03 Last updated: 2017-12-08Bibliographically approved
In thesis
1. From 2D to 3D Models of Electrical Conductivity based upon Magnetotelluric Data: Experiences from two Case Studies
Open this publication in new window or tab >>From 2D to 3D Models of Electrical Conductivity based upon Magnetotelluric Data: Experiences from two Case Studies
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Magnetotelluric measurements are among the few geophysical techniques capable of imaging the structure both in the shallow subsurface as well as the entire crust of the Earth. With recent technical and computational advances it has become possible to derive three-dimensional inversion models of the electrical conductivity from magnetotelluric data, thereby overcoming the problems arising from the simplified assumption of two-dimensionality in conventional two-dimensional modeling. The transition from two-dimensional to three-dimensional analysis requires careful reconsideration of the classical challenges of magnetotellurics: galvanic distortion, data errors, model discretization and resolution.This work presents two examples of magnetotelluric investigations, where a new three-dimensional inversion algorithm has been applied. The new models are compared with conventional two-dimensional models and combined with the results of other geophysical techniques like reflection seismics and electrical resistivity tomography. The first case presents magnetotelluric investigations of the Kristineberg mining area in the Skellefte district, northern Sweden. This study is part of a joint geophysical and geological project to investigate the present structure and evolution of the whole district. Together with reflection seismic and surface geological information a three-dimensional conductivity model, derived through the inversion of magnetotelluric data, was interpreted. A comparison with two-dimensional modeling gives insights into the capabilities and challenges of three-dimensional inversion strategies with respect to data sampling and model resolution.The second case presents a study of remediation monitoring  with geophysical methods after an oil blow-out in Trecate, Italy. A three-dimensional conductivity model was derived from radiomagnetotelluric measurements. In addition, two-dimensional joint inversion of radiomagnetotelluric and electrical tomography data was performed. Compared with electrical resistivity tomography, radiomagnetotelluric data is more sensitive to conductors and the derived three-dimensional inversion model resolves the vadose zone and the underlying aquifer.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. 58 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 890
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-165143 (URN)
Public defence
2012-02-17, Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2012-01-27 Created: 2012-01-03 Last updated: 2012-02-15Bibliographically approved

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Hübert, JulianeKalscheuer, ThomasPedersen, Laust B

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