Estimation of the Structural and Geomechanical Anisotropy in Fault Gouges Using 3D Micro-Computed Tomography (μ-CT).

Area of Science:

• Geology
• Geophysics
• Rock Mechanics

Background:

• Fault gouges are critical to shear deformation and instability in fault zones.
• Previous research on fault gouge evolution focused on micro-scale experiments with remolded or synthetic specimens.
• The 3D anisotropy of intact fault gouge structures at the core scale remains poorly understood.

Purpose of the Study:

• To investigate the 3D anisotropy of intact fault gouge structures at the core scale.
• To quantify the relationship between the spatial configuration of rock constituents and geomechanical behavior.
• To determine if core-scale structural anisotropy correlates with anisotropic shear resistance.

Main Methods:

• Acquisition of 3D micro-computed tomography (μ-CT) images of directionally cored gouge specimens.
• Statistical analysis to quantify the orientation of internal structures within fault gouges.
• Direct shear tests to assess the geomechanical behavior and frictional resistance.

Main Results:

• Undisturbed fault gouges display significant anisotropy parallel to the fault plane, even at the core scale.
• Direct shear tests reveal that fault gouge frictional resistance is anisotropic and related to the fault plane.
• A novel method confirms a correlation between core-scale structural anisotropy and anisotropic shear resistance.

Conclusions:

• Core-scale structural anisotropy is a key factor in the geomechanical behavior of fault gouges.
• The orientation of internal structures directly impacts the shear resistance of fault zones.
• This research provides a robust method for understanding fault gouge anisotropy and its implications for seismic activity.