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Solid Earth An interactive open-access journal of the European Geosciences Union
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Volume 9, issue 3
Solid Earth, 9, 683–698, 2018
https://doi.org/10.5194/se-9-683-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Solid Earth, 9, 683–698, 2018
https://doi.org/10.5194/se-9-683-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 29 May 2018

Research article | 29 May 2018

Permeability and seismic velocity anisotropy across a ductile–brittle fault zone in crystalline rock

Quinn C. Wenning1, Claudio Madonna1, Antoine de Haller2, and Jean-Pierre Burg1 Quinn C. Wenning et al.
  • 1Department of Earth Sciences, Institute of Geology, ETH Zurich, Zurich, Switzerland
  • 2Department of Earth Sciences, University of Geneva, Geneva, Switzerland

Abstract. This study characterizes the elastic and fluid flow properties systematically across a ductile–brittle fault zone in crystalline rock at the Grimsel Test Site underground research laboratory. Anisotropic seismic velocities and permeability measured every 0.1 m in the 0.7 m across the transition zone from the host Grimsel granodiorite to the mylonitic core show that foliation-parallel P- and S-wave velocities systematically increase from the host rock towards the mylonitic core, while permeability is reduced nearest to the mylonitic core. The results suggest that although brittle deformation has persisted in the recent evolution, antecedent ductile fabric continues to control the matrix elastic and fluid flow properties outside the mylonitic core. The juxtaposition of the ductile strain zone next to the brittle zone, which is bounded inside the two mylonitic cores, causes a significant elastic, mechanical, and fluid flow heterogeneity, which has important implications for crustal deformation and fluid flow and for the exploitation and use of geothermal energy and geologic waste storage. The results illustrate how physical characteristics of faults in crystalline rocks change in fault zones during the ductile to brittle transitions.

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Short summary
We measured the elastic and fluid flow properties in a ductile-brittle shear zone. The results suggest that although brittle deformation has persisted in the recent fault evolution, precursory ductile microstructure continues to control the petrophysical properties outside the fault core. The results are a glimpse into the evolutionary path of a shear zone during the ductile to brittle transition and are insightful for geothermal energy and geologic waste disposal exploitation and usage.
We measured the elastic and fluid flow properties in a ductile-brittle shear zone. The results...
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