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<p>In order to fully comprehend the effect of faults on fluid flow and mass transport, it is essential to determine the permeability distribution in the rock matrix surrounding such faults. In the present study, permeability measurements were performed in the vicinity of a subvertical Main Shaft Fault (MSF) at the Mizunami Underground Research Laboratory, Gifu Prefecture, central Japan. The permeability of granite exposed on a tunnel wall at depths of 200, 300, and 500&#xa0;m was measured using a probe permeameter at various distances from the MSF. The region of highest permeability showed a clear dependence on both the depth and the distance from the fault. At a depth of 300&#xa0;m, the highest permeability was observed at a distance of 30–40&#xa0;m from the MSF, whereas at a depth of 500&#xa0;m, high permeability was found in the vicinity of the MSF and a secondary fault. The cumulative frequency of fractures with a length ≥ 0.01&#xa0;m estimated by extrapolating a power law for the macroscopic fracture frequency showed a weak positive correlation with the permeability at a depth of 300&#xa0;m, but a negative or unclear correlation at a depth of 500&#xa0;m. This inconsistency is presumably caused by differences in the intensity and type of processes that modified the matrix permeability after formation of the damage zone at these two depths.</p>

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Depth and fault-dependent spatial variability of permeability in the rock matrix of Toki granite: A case study based on in-situ measurements in the Mizunami Underground Research Laboratory, central Japan

  • 期刊论文

  • 发表日期：

    2026年8月3日

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  • Koki Kashiwaya,
  • Taiki Kubo,
  • Masayuki Ishibashi,
  • Yohei Tada,
  • Katsuaki Koike

摘要

In order to fully comprehend the effect of faults on fluid flow and mass transport, it is essential to determine the permeability distribution in the rock matrix surrounding such faults. In the present study, permeability measurements were performed in the vicinity of a subvertical Main Shaft Fault (MSF) at the Mizunami Underground Research Laboratory, Gifu Prefecture, central Japan. The permeability of granite exposed on a tunnel wall at depths of 200, 300, and 500 m was measured using a probe permeameter at various distances from the MSF. The region of highest permeability showed a clear dependence on both the depth and the distance from the fault. At a depth of 300 m, the highest permeability was observed at a distance of 30–40 m from the MSF, whereas at a depth of 500 m, high permeability was found in the vicinity of the MSF and a secondary fault. The cumulative frequency of fractures with a length ≥ 0.01 m estimated by extrapolating a power law for the macroscopic fracture frequency showed a weak positive correlation with the permeability at a depth of 300 m, but a negative or unclear correlation at a depth of 500 m. This inconsistency is presumably caused by differences in the intensity and type of processes that modified the matrix permeability after formation of the damage zone at these two depths.