uu.seUppsala University Publications
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Investigation of groundwater resources using controlled-source radio magnetotellurics (CSRMT) in glacial deposits in Heby, Sweden
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. (Electromagnetic studies)
Geological Survey of Sweden. (Electromagnetic studies)
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. (Electromagnetic studies)
2011 (English)In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 73, no 1, 74-83 p.Article in journal (Refereed) Published
Abstract [en]

We have combined tensor radio magnetotelluric- (RMT, 15-250. kHz) and controlled source tensor magnetotelluric (CSTMT, 1-12. kHz) data for the mapping of aquifers in gravel formations lying in between crystalline bedrock and clay rich sediments in the Heby area some 40. km west of Uppsala in Sweden. The estimated transfer functions, the impedance tensor and the tipper vector generally satisfy 1D or 2D necessary conditions except for the lowest CSTMT frequencies where near field effects become more dominant.The data measured from 8 profiles were inverted with the Rebocc code of Siripunvaraporn and Egbert (2000) assuming plane wave conditions. This meant that only 12 frequencies in the range of 4-180kHz could be used. The four lowest frequencies of CSTMT in the range of 1-2.8kHz were excluded because of source effects. Data from all profiles were inverted with a starting model of 100Ω-m and a relative error floor of 0.02 on apparent resistivity, corresponding to less than 1° on phase. Tipper vectors are generally small except when source effects become dominant in the lowest frequencies of CSTMT and were therefore not used for inversion. Comparing with models derived from vertical electrical soundings, refraction and reflection seismic data as well as ground truth from exploration wells assessed the reliability of the deep part of the models. Furthermore we carried out a non-linear resolution analysis to better quantify the depth extent of the aquifers.The inverted models from the Heby area show well the thickness variations of glacial deposits overlying crystalline bedrock. Generally, the upper 20. m of the models have resistivities below 40 Ω-m, taken to represent clay rich formations. Below the clay layer resistivities increase to about 40-400 Ω-m, interpreted to represent sand/gravel formations with a maximum thickness of about 40. m and a width of several hundred metres. This is a potential aquifer that extends in approximately N-S direction for some kilometres.

Place, publisher, year, edition, pages
2011. Vol. 73, no 1, 74-83 p.
Keyword [en]
Controlled source, Radio magnetotelluric, Electromagnetic, Sediments, Resistivity
National Category
Geophysics
Research subject
Earth Science with specialization in Environmental Analysis; Hydrology; Geophysics with specialization in Solid Earth Physics
Identifiers
URN: urn:nbn:se:uu:diva-102739DOI: 10.1016/j.jappgeo.2010.11.008ISI: 000287275100010OAI: oai:DiVA.org:uu-102739DiVA: diva2:216661
Available from: 2009-05-11 Created: 2009-05-11 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Controlled Source Radiomagnetotelluric (CSRMT) Applications in Environmental and Resource Exploration
Open this publication in new window or tab >>Controlled Source Radiomagnetotelluric (CSRMT) Applications in Environmental and Resource Exploration
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2009. 66 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 655
Keyword
Magnetotelluric, radio magnetotelluric, controlled-source tensor magnetotelluric, plane wave, near surface geophysics, sediment, fracture zone, inversion, forward modelling, near field effect, two-dimensional model, three-dimensional model, resolution
National Category
Geophysics
Research subject
Earth Sciences with Specialization Environmental Analysis; Hydrology; Mineral Chemistry, Petrology and Tectonics
Identifiers
urn:nbn:se:uu:diva-102750 (URN)978-91-554-7550-5 (ISBN)
Public defence
2009-06-05, Axel Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2009-05-14 Created: 2009-05-11 Last updated: 2009-05-25Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full text

Authority records BETA

Ismail, NazliPedersen, Laust

Search in DiVA

By author/editor
Ismail, NazliPedersen, Laust
By organisation
Geophysics
In the same journal
Journal of Applied Geophysics
Geophysics

Search outside of DiVA

GoogleGoogle Scholar

doi
urn-nbn

Altmetric score

doi
urn-nbn
Total: 552 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf