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High-resolution 3D reflection seismic investigation over a quick-clay landslide scar 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.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
(Geological Survey of Sweden (SGU))
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2014 (English)In: Geophysics, ISSN 0016-8033, E-ISSN 1942-2156, Vol. 79, no 2, B97-B107 p.Article in journal (Refereed) Published
Abstract [en]

Quick-clay landslides often occur in the northern hemisphere in areas that were covered by Pleistocene glaciation. They are particularly common along the shorelines of the Göta River in southwestern Sweden. Characterization of potential landslide areas and identification of features that indicate high risk are necessary to better understand the triggering mechanisms of these events. Therefore, an intensive characterization project has been initiated at the location of the Fråstad landslide in Sweden. Part of the characterization program included the acquisition of 3D reflection seismic data to image structures in the normally consolidated sediments, as well as the bedrock topography below the landslide scar. Two seismic horizons within the glacial and post-glacial sediments were observed. The shallowest seismic horizon (here referred to as S1) corresponds to a coarse-grained layer that was previously detected by eight geotechnical boreholes located within the 3D survey area. Discontinuities in S1, mapped by the 3D reflection seismic data, occur across a zone that correlates with the landslide scar boundary, suggesting that this zone may have played a role in triggering and/or in limiting the extension of the landslide. If S1 is truncated by or mixed with clays in this zone, then the outflow of water from the permeable S1 into the clays above may have increased the amount of quick-clays above this zone. The increased outflow of water may also have caused a higher pore-water pressure south of the zone, which in turn could have acted as a trigger for the landslide. This study shows the potential of using the 3D reflection seismic method as a complement to drilling and other geophysical methods when performing landslide site investigations. It also demonstrates the importance of further investigating the relationship between 3D subsurface geometries and landslide development.

Place, publisher, year, edition, pages
2014. Vol. 79, no 2, B97-B107 p.
National Category
Geophysics
Identifiers
URN: urn:nbn:se:uu:diva-211211DOI: 10.1190/GEO2013-0225.1ISI: 000336918700007OAI: oai:DiVA.org:uu-211211DiVA: diva2:665939
Available from: 2013-11-21 Created: 2013-11-21 Last updated: 2017-12-06Bibliographically approved
In thesis
1. 2D and 3D Reflection Seismic Studies over Scandinavian Deformation Zones
Open this publication in new window or tab >>2D and 3D Reflection Seismic Studies over Scandinavian Deformation Zones
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The study of deformation zones is of great geological interest since these zones can separate rocks with different characteristics. The geometry of these structures with depth is important for interpreting the geological history of an area. Paper I to III present 2D reflection seismic data over deformation zones targeting structures in the upper 3-4 km of the crust. These seismic profiles were acquired with a crooked-line recording geometry. 2D seismic processing assumes a straight recording geometry. Most seismic processing tools were developed for sub-horizontally layered structures. However, in the crystalline rocks in Scandinavia more complex structures with contrasting dip directions and folding are common. The crooked-line recording geometries have the benefit of sampling a 3D volume. This broader sampling can be used to gain knowledge about the true geometry of subsurface structures. Correlation with geological maps and other geophysical data along with seismic data modeling can be used to differentiate reflections from faults or fracture zones from other reflectivity, e.g. mafic bodies. Fault and fracture zones may have a large impedance contrast to surrounding rocks, while ductile shear zones usually do not. The ductile shear zones can instead be interpreted based on differing reflectivity patterns between domains and correlations with geology or magnetic maps. Paper IV presents 3D reflection seismic data from a quick-clay landslide site in southern Sweden. The area is located in a deformation zone and structures in unconsolidated sediments may have been influenced by faults in the bedrock. The main target layer is located at only 20 m depth, but good surface conditions during acquisition and careful processing enabled a clear seismic image of this shallow layer to be obtained.The research presented in this thesis provides increased knowledge about subsurface structures in four geologically important areas. The unconventional processing methods used are recommended to future researchers working with data from crooked-line recording geometries in crystalline environments. The imaging of shallow structures at the quick-clay landslide site shows that the 3D reflection seismic method can be used as a complement to other geophysical measurements for shallow landslide site investigations.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. 57 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1102
Keyword
Azimuthal binning, Crooked-line geometry, Cross-dip, Fault zone, Hard rock seismics, MTFC, Quick clay, Shear zone, UDZ
National Category
Geophysics
Research subject
Geophysics with specialization in Solid Earth Physics
Identifiers
urn:nbn:se:uu:diva-211215 (URN)978-91-554-8817-8 (ISBN)
Public defence
2014-01-31, Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 10:00 (English)
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Supervisors
Available from: 2014-01-09 Created: 2013-11-21 Last updated: 2014-01-24

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Lundberg, EmilMalehmir, AlirezaJuhlin, ChristopherAndersson, Magnus

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