Anisotropic roughness evolution of triaxially fractured granite
Eric Burdette, N. M. Beeler, Brian D. Kilgore, & David A. LocknerSubmitted August 30, 2026, SCEC Contribution #15438, 2026 SCEC Annual Meeting Poster #TBD
To investigate the evolution of fault-surface topography we fractured intact 2.75-inch-diameter cylinders of Westerly granite were fractured in triaxial compression at 50 MPa confining pressure and room temperature. The generated surface heights were measured using a white-light profilometer. To characterize roughness modifications resulting from slip, one fractured samples was rejacketed, and subjected to an additional 5 mm of axial deformation. One-dimensional power spectral density analyses demonstrate that the fractured surfaces possess self-affine, mildly anisotropic geometries. Both slip parallel and slip perpendicular profiles share Hurst exponents of 0.75-0.85. Slip-parallel directions are consistently smoother by a factor of 1.2-1.4 across all measured scales. Overall surface amplitudes exhibit height-to-length ratios near 0.01, falling intermediately between values reported for exhumed natural faults and unconfined laboratory fractures. Furthermore, distributions of surface height significantly depart from Gaussian behavior at short lag distances, establishing the presence of geometric intermittency (local, large changes in surface height).
Wear metrics on the recovered surfaces of 0.38-0.68 mm3/mm2 per mm slip indicate substantial material removal during fracture and slip. The wear rate is consistent with previous laboratory studies of sandstone at high normal stresses. Despite substantial gouge production across an additional 5 mm of slip, no significant reduction in roughness amplitude is observed. The absence of smoothing contrasts with progressive attenuation trajectories documented in low normal stress direct-shear experiments and several field studies, suggesting that confined dynamic fracture and active wear mechanisms in strong crystalline rock at high normal stress do not necessarily smooth fault surfaces.
Key Words
roughness, fracture, triaxial
Citation
Burdette, E., Beeler, N. M., Kilgore, B. D., & Lockner, D. A. (2026, 08). Anisotropic roughness evolution of triaxially fractured granite. Poster Presentation at 2026 SCEC Annual Meeting.
Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)
