Quantitative anisotropies of palaeopermeability in a strike-slip fault damage zone: Insights from micro-CT analysis and numerical simulations

• Published in: Tectonophysics 2021-07, Vol.810, p.228873, Article 228873
• Main Authors: Gomila, R., Arancibia, G., Nehler, M., Bracke, R., Morata, D., Cembrano, J.
• Format: Article
• Language: English
• Subjects: 3D Permeability modeling; Anisotropy; Computational fluid dynamics; Computed tomography; Damage; Distribution; Earthquakes; Ellipsoids; Fault zone palaeopermeability; Fluids; Lattice-Boltzmann method; Mathematical models; Microfracture; Numerical simulations; Percolation; Permeability; Permeability anisotropy; Seismic activity; Slip; Spatial distribution; Tensors; Three dimensional models; Tomography; X-Ray micro-computed tomography
• ISSN: 0040-1951; 1879-3266
• DOI: 10.1016/j.tecto.2021.228873

Fracturing and damage around faults related to seismogenesis can enhance hydrothermal fluid percolation, causing mineral precipitation. This study uses hydrothermally sealed microfractures across an ancient exhumed fault to unravel the 3D-spatial distribution of fault damage and related anisotropy in permeability. We studied the fault damage zone of the Jorgillo Fault, a left-lateral strike-slip fault, exposed by ca. 20 km in the Atacama Fault System, northern Chile. The study was conducted by addressing the 3D-spatial distribution of the microfracture network through X-ray micro-computed tomography and palaeopermeability modeling using a computational fluid dynamic approach, thus assessing mm-scale fault-related permeability tensors. 3D modeled fault-directed permeability ellipsoids on both sides of the fault core are transverse anisotropic, where palaeopermeability (matrix permeability) in the fault-parallel plane is higher than across-strike of the Jorgillo Fault (2.4 and 1.9 times in the eastern and western block of the fault, respectively). Modeled 3D permeability values (ca. 10−11 to 10−15 m2) show a mean overestimation factor of 8.4 of the estimated 2D permeability (ca. 10−9 to 10−12 m2). Permeability anisotropy distribution in the damage zone is related to off-fault damage generation, and could be explained by tip propagation fault growth and dynamic rupture due to earthquakes under the fault-valve mechanism. Whereas the fault would act as an impermeable seal except for post-failure, when it became highly permeable for fluids. •Sealed microfractures 3D-spatial distribution was assessed with X-ray μ-CT.•Fault damage zone palaeopermeability was modeled with the Lattice-Boltzmann Method.•The mean normal components of the permeability tensors are transverse anisotropic.•Along-fault plane palaeopermeability is higher than across-strike of the fault.