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Geophysical characterization of areas prone to quick-clay landslides using radio-magnetotelluric and seismic methods
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.
Geol Survey Sweden, Villavagen 18, SE-75128 Uppsala, Sweden..
2016 (English)In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 677, 248-260 p.Article in journal (Refereed) Published
Resource type
Text
Abstract [en]

Landslides attributed to quick clays have not only considerable influences on surface geomorphology, they have caused delays in transportation systems, environmental problems and human fatalities, especially in Scandinavia and North America. If the subsurface distributions of quick clays are known, potential damages can be mitigated and the triggers of landslides can better be studied and understood. For this purpose, new radio-magnetotelluric (RMT) and seismic data were acquired in an area near the Gota River in southwest Sweden that contains quick clays and associated landslides. High-resolution data along 4 new lines, in total 3.8 km long, were acquired and merged with earlier acquired data from the site. Velocity and resistivity models derived from first breaks and RMT data were used to delineate subsurface geology, in particular the bedrock surface and coarse-grained materials that overlay the bedrock. The latter often are found underlying quick clays at the site. Comparably high resistivity and sometimes high-velocity regions within marine clays are attributed to a combination of leached salt from marine clays or potential quick clays and coarse-grained materials. The resistivity and tomographic velocity models suggest a much larger role of the coarse-grained materials at the site than previously thought, but they also suggest two different scenarios for triggering quick-clay landslides at the site. These scenarios are related to the erosion of the riverbank, increased pore-pressure and surface topography when close to the river and human activity when away from the river and where bowl-shaped bedrock surrounds the sediments.

Place, publisher, year, edition, pages
2016. Vol. 677, 248-260 p.
Keyword [en]
Quick clay, Landslide, Radio-magnetotelluric, Seismic, Tomography, Coarse grain
National Category
Geophysics
Identifiers
URN: urn:nbn:se:uu:diva-299505DOI: 10.1016/j.tecto.2016.04.020ISI: 000377311700018OAI: oai:DiVA.org:uu-299505DiVA: diva2:949692
Funder
Swedish Research Council Formas, 25220121907
Available from: 2016-07-22 Created: 2016-07-22 Last updated: 2017-08-03Bibliographically approved
In thesis
1. Joint inversion and integration of multiple geophysical data for improved models of near-surface structures
Open this publication in new window or tab >>Joint inversion and integration of multiple geophysical data for improved models of near-surface structures
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Geophysical methods are non-invasive and allow an effective way of understanding subsurface structures and their physical properties. One of the main challenges is the often non-uniqueness of the geophysical models and that several different models can explain a dataset to an agreeable fit. Moreover, noise and limitations in resolution, which are inherent to field data, are additional obstacles for obtaining a true physical property model of the subsurface. Facing all these challenges, geophysicists have dedicated their efforts for decades to recover models that represent, as close as possible, the true subsurface. Joint inversion and integration of multiple geophysical data are two main approaches that I studied to better resolve subsurface structures. I further used these approaches, together with new software and hardware implementations for data acquisition and inversion, for near-surface applications. 

In this thesis, radio-magnetotelluric (RMT), boat-towed RMT, boat-towed controlled source MT (CSMT), electrical resistivity tomography (ERT), and first-arrival traveltime tomography are jointly used for quick clay investigations and fracture zone delineation under shallow water-bodies. The joint approach, as compared with any individual method, shows a better ability to both resolve the geological targets and to assist in understanding the subsurface geology that hosts these targets. For examples: by performing the joint inversion of lake-floor ERT and boat-towed RMT data, a fracture zone is better delineated with greater details compared with single inversion; by employing boat-towed CSMT measurements and jointly inverting with boat-towed RMT data, the subsurface structures, especially at greater depth, are better resolved than by inverting each dataset alone.

During my PhD studies, two types of new implementations were employed. (1) Boat-towed data acquisition system was implemented to expand the RMT and CSMT method from land to shallow-water applications. This is significant since many large-scale underground infrastructures are likely to cross these water zones (for example multi-lane train or bypass tunnels, such as the Stockholm bypass). (2) The modification of a well-structured code EMILIA allows joint inversion of boat-towed RMT and lake-floor ERT datasets, and the modification of another well-structured code MARE2DEM can accurately model high frequency CSMT data and handle joint inversion of boat-towed RMT and boat-towed CSMT datasets. Thus, the code modification as another type of new implementation guarantees the success of near-surface applications using the boat-towed RMT and CSMT data acquisition systems.

Studies conducted during my PhD work, included under the SEG-GWB (the Society of Exploration Geophysicists - Geoscientists Without Borders) program and the TRUST (TRansparent Underground STructure) umbrella project, are useful for near-surface applications including, for examples, engineering purposes such as planning of underground infrastructures, site characterization in connection with energy or waste storage, and geohazard investigations.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. 65 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1536
Keyword
joint inversion, ERT, RMT, CSRMT, boat-towed, tomography
National Category
Geophysics
Research subject
Geophysics with specialization in Solid Earth Physics
Identifiers
urn:nbn:se:uu:diva-327096 (URN)978-91-513-0018-4 (ISBN)
Public defence
2017-09-18, Hambergsalen, Villavägen 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2017-08-29 Created: 2017-08-03 Last updated: 2017-09-08

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