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

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Author Wenning Quinn C., Madonna Claudio, de Haller Antoine, Burg Jean-Pierre,
Project Exploration and characterization of deep underground reservoirs
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Original article (peer-reviewed)

Journal Solid Earth
Volume (Issue) 9(3)
Page(s) 683 - 698
Title of proceedings Solid Earth
DOI 10.5194/se-9-683-2018

Open Access

URL http://doi.org/10.5194/se-9-683-2018
Type of Open Access Publisher (Gold Open Access)

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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