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Main Title: Seismic anisotropy of Opalinus Clay: tomographic investigations using the infrastructure of an underground rock laboratory (URL)
Author(s): Esefelder, Roman
Wawerzinek, Britta
Lüth, Stefan
Giese, Rüdiger
Krawczyk, Charlotte M.
Type: Article
Abstract: Seismic anisotropy and attenuation make claystone formations difficult to characterize. On the other hand, in many geotechnical environments, precise knowledge of structure and elastic properties of clay formations is needed. In crystalline and rock salt underground structures, high-resolution seismic tomography and reflection imaging have proven a useful tool for structural and mechanical characterization at the scale of underground infrastructure (several deca- to hundreds of meters). This study investigates the applicability of seismic tomography for the characterization of claystone formations from an underground rock laboratory under challenging on-site conditions including anisotropy, strong attenuation and restricted acquisition geometry. The seismic tomographic survey was part of a pilot experiment in the Opalinus Clay of the Mont Terri Rock Laboratory, using 3-component geophones and rock anchors, which are installed 2 m within the rock on two levels, thus suppressing effects caused by the excavation damage zone. As a source, a pneumatic impact source was used. The survey covers two different facies types (shaly and carbonate-rich sandy), for which the elliptical anisotropy is calculated for direct ray paths by fitting an ellipse to the separated data for each facies. The tomographic inversion was done with a code providing a good grid control and enabling to take the seismic anisotropy into account. A-priori anisotropy can be attributed to the grid points, taking various facies types or other heterogeneities into account. Tomographic results, compared to computations using an isotropic velocity model, show that results are significantly enhanced by considering the anisotropy and demonstrate the ability of the approach to characterize heterogeneities of geological structures between the galleries of the rock laboratory.
Subject(s): seismic anisotropy
seismic tomography
Opalinus Clay
Mont Terri
underground rock laboratory
Issue Date: 27-Nov-2021
Date Available: 11-Jan-2022
Language Code: en
DDC Class: 550 Geowissenschaften
Sponsor/Funder: BMBF, 02NUK053D, Verbundprojekt iCross: Integrität von Endlagersystemen für radioaktive Abfälle - Skalenübergreifendes Systemverständnis und Systemanalyse, Teilprojekt D
Journal Title: Swiss Journal of Geosciences
Publisher: Springer Nature
Volume: 114
Article Number: 21
Publisher DOI: 10.1186/s00015-021-00398-2
EISSN: 1661-8734
ISSN: 1661-8726
TU Affiliation(s): Fak. 6 Planen Bauen Umwelt » Inst. Angewandte Geowissenschaften
Appears in Collections:Technische Universität Berlin » Publications

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