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Integrated 2D modeling and interpretation of geophysical and geotechnical data to delineate quick clays at a landslide site in southwest Sweden
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
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2014 (English)In: Geophysics, ISSN 0016-8033, E-ISSN 1942-2156, Vol. 79, no 4, 61-75 p.Article in journal (Refereed) Published
Abstract [en]

Radio Magnetotellurics (RMT), Electrical Resistivity Tomography (ERT) and high-resolution reflection seismic data were collected along four lines to image the geometry and physical properties of geological structures at a quick-clay landslide site in southwest Sweden. The site is situated in the Göta River valley where the normally consolidated materials mainly consist of glacial and post-glacial sediments. Geotechnical data suggest presence of quick clays above coarse-grained layers. These layers play a key role in the formation of quick clays and landslide triggering. The RMT and ERT data were individually and jointly inverted in 2D to study the resolution of resulting models for each data set. The resistivity models from the joint inversions demonstrate superior resolution and accuracy than individual ones. The geometry and location of shallower structures resolved in the 2D resistivity models from joint RMT+ERT inversions correlate well with those imaged in the reflection seismic data and observed in the existing geotechnical boreholes.  The models are poor in resolving deeper resistive bedrock at locations where the thickness of the conductive overburden exceeds a certain limit. However, information from the reflection seismic data could be used to estimate the depth to the top of the bedrock along all the four lines. Comparison between the geotechnical data and the resistivity models suggests that quick clays overlying the coarse-grained layer have higher electrical resistivity than the marine clays. The obtained results were further validated and refined by performing synthetic tests. This study shows that integration of ERT and RMT data with reflection seismic data is ideal for quick-clay landslide studies especially when the clay materials are thick.

Place, publisher, year, edition, pages
2014. Vol. 79, no 4, 61-75 p.
National Category
Geophysics
Research subject
Geophysics with specialization in Solid Earth Physics
Identifiers
URN: urn:nbn:se:uu:diva-229913DOI: 10.1190/GEO2013-0201.1ISI: 000341985500017OAI: oai:DiVA.org:uu-229913DiVA: diva2:738246
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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Publisher's full texthttp://dx.doi.org/10.1190/geo2013-0201.1

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Shan, ChunlingMalehmir, Alireza

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