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Integration of controlled-source and radio-magnetotellurics, electrical resistivity tomography and reflection seismics to delineate 3D structures of a quick-clay landslide site in southwest Sweden
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences. (Geophysics)
Geol Survey Sweden, Uppsala, Sweden.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences. (Geophysics)
Geol Survey Sweden, Uppsala, Sweden.
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2016 (English)In: Geophysics, ISSN 0016-8033, E-ISSN 1942-2156, Vol. 81, no 1, B13-B29 p.Article in journal (Other academic) Published
Abstract [en]

Three-dimensional radio magnetotelluric (RMT), controlled-source radio magnetotelluric (CSRMT), electrical resistivity tomography (ERT), and high-resolution reflection seismic data were acquired at a quick-clay landslide site close to the Göta River in southwest Sweden. These data were collected with the main objectives of evaluating the performance of each method and delineating different subsurface materials down to the bedrock, which in turn control a peculiar and hazardous retrogressive-type landslide. These materials consist of mainly marine clays, quick clays, sand to gravel and the crystalline bedrock. The RMT, CSRMT and ERT data were inverted separately using 3D inversion schemes and the independent results from 3D processing of reflection seismic data together with the existing geotechnical data were used for their interpretations. The 3D CSRMT resistivity model shows the highest depth penetration and well resolves the geometry of the bedrock. The RMT and ERT models, however, show better resolution closer to the surface because of their denser data coverage compared with the CSRMT data. Considerable correlations in resolving a coarse-grained layer and the bedrock were observed between the CSRMT model and the 3D reflection seismic data. Because an Occam-type regularization was used in the inversion, the lateral and depth extent of the quick clays cannot accurately be determined just by using the resistivity models. The depth to the top of the resistive crystalline bedrock is to some extent uncertain. Comparisons with the borehole data suggest that the resistivity models are poor in resolving the sharp boundary between the quick clays and their underlying more resistive coarse-grained materials. The upper boundary of the more conductive marine clays underlain by the coarse-grain materials was well modeled by the CSRMT data. This study illustrates the potentials of 3D geophysical data especially when different types are collected and particularly for better site characterizations.

Place, publisher, year, edition, pages
2016. Vol. 81, no 1, B13-B29 p.
National Category
Geophysics Other Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:uu:diva-229915DOI: 10.1190/GEO2014-0386.1ISI: 000377880100004OAI: oai:DiVA.org:uu-229915DiVA: diva2:738249
Available from: 2014-08-16 Created: 2014-08-16 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Natural and Controlled Source Magnetotelluric Data Processing and Modeling
Open this publication in new window or tab >>Natural and Controlled Source Magnetotelluric Data Processing and Modeling
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, four studies using different geophysical electromagnetic methods are presented. In the first study dealing with airborne measurements, the noise response due to the rotation of the aircraft and the aircraft itself as a metallic conductive body on the Earth's electromagnetic response in very low frequency and low frequency band was investigated. The magnetic fields are independent of the aircraft in the VLF band and part of the LF band. But at higher frequencies (above 100 kHz), the signals are more influenced by the aircraft. The aircraft also generates its own noise frequencies which are mixed with the radio transmitter signals. The second and third studies are applications of radio-, controlled source-magnetotellurics and electrical resistivity tomography methods at a quick-clay landslide site in southwest Sweden. The data are processed and modeled in 2D and 3D, and the models are compared with high-resolution seismic and geotechnical data. The obtained results were further validated and refined by performing synthetic tests in the second study. The third study shows that the 3D models provide larger and more continuous volume of the quick clay structure than traditional 2D models. Both studies have shown that integrated application of geophysical methods for landslides is ideal. Quick clays often overlie the coarse-grained layers showing an increase of resistivity values in the models. In the fourth study, a new audio magnetotelluric data acquisition technique is developed and is named moving magnetotellurics (MMT). In this new technique, the magnetic sensors are placed on the ground and only 15 to 20 minutes data are acquired for each station, which usually is enough to cover the frequency range 30-300 Hz. The new technique is more efficient and convenient than the traditional magnetotelluric method, and test measurements have shown that it is an applicable method in shallow depth studies.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. 53 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1165
Keyword
Geophysics, Airborne Electromagnetic Method, Radio Magnetotellurics, Controlled Source Magnetotellurics, Electrical Resistivity Tomography, Moving Magnetotellurics, 2D inversion, 3D inversion
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-229917 (URN)978-91-554-9001-0 (ISBN)
Public defence
2014-10-03, Hambergsalen, Villavägen 16, Uppsala, 10:00 (English)
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Supervisors
Available from: 2014-09-10 Created: 2014-08-16 Last updated: 2016-05-13

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Shan, ChunlingMalehmir, AlirezaLundberg, Emil

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