EGU21-12483
https://doi.org/10.5194/egusphere-egu21-12483
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Seismic anisotropy in metamorphic rocks from the COSC-1 borehole, Sweden: A cross-scale investigation from thin section analysis to seismic scales

Felix Kästner1, Simona Pierdominici1, Alba Zappone3,4,5, Luiz F. G. Morales3,4, Anja M. Schleicher1, Franziska D. H. Wilke1, and Christian Berndt2
Felix Kästner et al.
  • 1Helmholtz Centre Potsdam, German Research Centre for Geosciences GFZ, 14473 Potsdam, Germany
  • 2GEOMAR Helmholtz Centre for Ocean Research Kiel, 24148 Kiel, Germany
  • 3Department of Earth Sciences, ETH Zürich, 8092 Zurich, Switzerland
  • 4Scientific Center for Optical and Electron Microscopy (ScopeM), ETH Zürich, 8093 Zurich, Switzerland
  • 5Swiss Seismological Service, 8092 Zurich, Switzerland

Metamorphic and deformed rocks in thrust zones show particularly high seismic anisotropy causing challenges for seismic imaging and interpretation. A good example is the Seve Nappe Complex in Jämtland, Sweden, an exhumed orogenic thrust zone characterized by a strong but incoherent seismic reflectivity and considerable seismic anisotropy. However, only little is known about the origin of the anisotropy in relation to composition, structural influences, and implications for measurements at different seismic scales. We present an integrative study of the seismic anisotropy at different scales combining mineralogical composition, microstructural analyses and seismic laboratory experiments from samples of the 2.5 km-deep COSC-1 borehole. While there is a pronounced crystallographic preferred orientation in most of the core samples, variations in anisotropy correlate strongly with bulk mineral composition and dominant core lithology. Based on three major lithologic different facies (felsic gneiss, amphibole-rich rocks, and mica schists), we propose an anisotropy model for the full length of the borehole, which indicates two prevailing anisotropic units. Comparison of laboratory seismic measurements and electron-backscatter diffraction (EBSD) data reveals a strong scale-dependence, which is more pronounced in the highly deformed, heterogeneous samples. This highlights the need for comprehensive cross-validation of microscale anisotropy analyses with additional lithological data when integrating seismic anisotropy through seismic scales.

How to cite: Kästner, F., Pierdominici, S., Zappone, A., Morales, L. F. G., Schleicher, A. M., Wilke, F. D. H., and Berndt, C.: Seismic anisotropy in metamorphic rocks from the COSC-1 borehole, Sweden: A cross-scale investigation from thin section analysis to seismic scales, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12483, https://doi.org/10.5194/egusphere-egu21-12483, 2021.

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