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High resolution reflection seismic profiling over the Tjellefonna fault in the More-Trondelag Fault Complex, Norway
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.
2012 (English)In: SOLID EARTH, ISSN 1869-9510, Vol. 3, no 1, 175-188 p.Article in journal (Refereed) Published
Abstract [en]

The More-Trondelag Fault Complex (MTFC) is one of the most prominent fault zones of Norway, both onshore and offshore. In spite of its importance, very little is known of the deeper structure of the individual fault segments comprising the fault complex. Most seismic lines have been recorded offshore or focused on deeper structures. This paper presents results from two reflection seismic profiles, located on each side of the Tingvollfjord, acquired over the Tjellefonna fault in the southeastern part of the MTFC. Possible kilometer scale vertical offsets, reflecting large scale northwest-dipping normal faulting, separating the high topography to the southeast from lower topography to the northwest have been proposed for the Tjellefonna fault or the Baeverdalen lineament. In this study, however, the Tjellefonna fault is interpreted to dip approximately 50-60 degrees towards the southeast to depths of at least 1.3 km. Travel-time modeling of reflections associated with the fault was used to establish the geometry of the fault structure at depth, while detailed analysis of first P-wave arrivals in shot gathers, together with resistivity profiles, were used to define the near surface geometry of the fault zone. A continuation of the structure on the northeastern side of the Tingvollfjord is suggested by correlation of an in strike direction P-S converted reflection (generated by a fracture zone) seen on the reflection data from that side of the Tingvollfjord. The reflection seismic data correlate well with resistivity profiles and recently published near surface geophysical data. A highly reflective package forming a gentle antiform structure was also identified on both seismic profiles. This structure could be related to the folded amphibolite lenses seen on the surface or possibly by an important boundary within the gneissic basement rocks of the Western Gneiss Region. The fold hinge line of the structure is parallel with the Tjellefonna fault trace suggesting that the folding and faulting may have been related.

Place, publisher, year, edition, pages
2012. Vol. 3, no 1, 175-188 p.
Keyword [en]
Western Gneiss Region, Central Norwegian Caledonides, Northern North-Sea, Mid-Norway, Continental-Margin, Evolution, Zone, Deformation, Sweden, Model
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:uu:diva-185224DOI: 10.5194/se-3-175-2012ISI: 000309884400014OAI: oai:DiVA.org:uu-185224DiVA: diva2:571076
Available from: 2012-11-21 Created: 2012-11-21 Last updated: 2017-01-25Bibliographically 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)
Opponent
Supervisors
Available from: 2014-01-09 Created: 2013-11-21 Last updated: 2014-01-24

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