Variation of Hydraulic Properties Due to Dynamic Fracture Damage: Implications for Fault Zones

Aben, F. M.; Doan, Mai‐Linh; Mitchell, Thomas M.

doi:10.1029/2019jb018919

Cited by 7 publications

(6 citation statements)

References 91 publications

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“…Using the porosity measured in the tomograms, the initial porosity of each rock core is close to zero. This monzonite has a mean grain size of 450 µm (Aben et al, 2016). The large grain size relative to the sample size may cause the representative elementary volume (REV) of the system to approach the size of the sample.…”

Section: In Situ X-ray Tomographymentioning

confidence: 99%

The competition between fracture nucleation, propagation, and coalescence in dry and water-saturated crystalline rock

2021

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Abstract. The continuum of behavior that emerges during fracture network development in crystalline rock may be categorized into three end-member modes: fracture nucleation, isolated fracture propagation, and fracture coalescence. These different modes of fracture growth produce fracture networks with distinctive geometric attributes, such as clustering and connectivity, that exert important controls on permeability and the extent of fluid–rock interactions. To track how these modes of fracture development vary in dominance throughout loading toward failure and thus how the geometric attributes of fracture networks may vary under these conditions, we perform in situ X-ray tomography triaxial compression experiments on low-porosity crystalline rock (monzonite) under upper-crustal stress conditions. To examine the influence of pore fluid on the varying dominance of the three modes of growth, we perform two experiments under nominally dry conditions and one under water-saturated conditions with 5 MPa of pore fluid pressure. We impose a confining pressure of 20–35 MPa and then increase the differential stress in steps until the rock fails macroscopically. After each stress step of 1–5 MPa we acquire a three-dimensional (3D) X-ray adsorption coefficient field from which we extract the 3D fracture network. We develop a novel method of tracking individual fractures between subsequent tomographic scans that identifies whether fractures grow from the coalescence and linkage of several fractures or from the propagation of a single fracture. Throughout loading in all of the experiments, the volume of preexisting fractures is larger than that of nucleating fractures, indicating that the growth of preexisting fractures dominates the nucleation of new fractures. Throughout loading until close to macroscopic failure in all of the experiments, the volume of coalescing fractures is smaller than the volume of propagating fractures, indicating that fracture propagation dominates coalescence. Immediately preceding failure, however, the volume of coalescing fractures is at least double the volume of propagating fractures in the experiments performed at nominally dry conditions. In the water-saturated sample, in contrast, although the volume of coalescing fractures increases during the stage preceding failure, the volume of propagating fractures remains dominant. The influence of stress corrosion cracking associated with hydration reactions at fracture tips and/or dilatant hardening may explain the observed difference in fracture development under dry and water-saturated conditions.

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Section: In Situ X-ray Tomographymentioning

confidence: 99%

The competition between fracture nucleation, propagation, and coalescence in dry and water-saturated crystalline rock

2021

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“…However, roughness may also control the large‐scale pattern if a larger amount of slip in multiple events would be considered in those simulations. In experiments looking specifically at the contribution of damage during dynamic failure of initially intact granite show that a wider damage zone results in comparison to controlled quasistatic failure (Aben et al., 2020). Erickson et al.…”

Section: Introductionmentioning

confidence: 99%

“…However, roughness may also control the large-scale pattern if a larger amount of slip in multiple events would be considered in those simulations. In experiments looking specifically at the contribution of damage during dynamic failure of initially intact granite show that a wider damage zone results in comparison to controlled quasistatic failure (Aben et al, 2020). Erickson et al (2017) modeled cycles of quasidynamic ruptures on a vertical, planar, strike-slip fault in an antiplane configuration and showed a progressive accumulation of damage particularly on the shallow part of the fault.…”

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confidence: 99%

The Effect of Fault Roughness and Earthquake Ruptures on the Evolution and Scaling of Fault Damage Zones

Tal¹,

Faulkner

2022

JGR Solid Earth

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Fault damage zones dominate the mechanical, hydraulic and seismological properties of faults yet the relative contributions from processes leading to their development and growth is obscure. In this study, we investigate the damage development related to slip on rough faults and passage of earthquake ruptures. We compare the cumulative damage with slip and damage distribution from numerical models against field data from exhumed faults with slip less than 3.5 m within the Atacama Fault Zone in northern Chile. Models are constrained by experimentally determined mechanical properties of the host rock. We perform simulations of damage accumulation during quasistatic slip on rough faults and during sequences of earthquakes on planar and rough faults governed by rate and state friction laws. Both sets of simulations include Drucker–Prager rheology of the bulk to identify off‐fault damage where the yield stress is exceeded. Our results indicate that the extent and distribution of damage depend on the characteristics of fault roughness, amount of slip, and, when present, the intensity and variability of dynamic ruptures. When typical values for fault roughness are used, the scaling of damage zone width versus slip during quasistatic slip is comparable to that observed in the field data. Earthquake rupture on smooth faults by itself does not explain the field data. Simulations of earthquake sequences on rough faults leads to significantly larger damage zone widths with slip than that observed in the field data, suggesting the development of damage for small displacement is dominated by quasistatic slip on rough faults.

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“…During shear failure, off‐fault deformation caused directly by the stress concentration around the rupture tip as part of Γ off precedes most of the off‐fault deformation from slip on a rough fault, since the amount of slip within the rupture tip process zone is negligible. Off‐fault deformation, and particularly off‐fault fracturing, changes the mechanical and hydraulic properties of fault damage zone rock, and thus the constituent dissipative processes of Γ off affect fault damage zone properties at an early stage during shear failure (Aben et al., 2020). This can have a feedback on rupture, slip, and ground motion; rupture simulations show that reduced mechanical properties in the fault damage zone affect fault slip (Cappa et al., 2014) and slip velocity (Andrews, 1976, 2005; Dunham et al., 2011).…”

Section: Introductionmentioning

confidence: 99%

Off‐Fault Damage Characterization During and After Experimental Quasi‐Static and Dynamic Rupture in Crustal Rock From Laboratory P Wave Tomography and Microstructures

2020

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Elastic strain energy released during shear failure in rock is partially spent as fracture energy Γ to propagate the rupture further. Γ is dissipated within the rupture tip process zone, and includes energy dissipated as off‐fault damage, Γoff. Quantifying off‐fault damage formed during rupture is crucial to understand its effect on rupture dynamics and slip‐weakening processes behind the rupture tip, and its contribution to seismic radiation. Here, we quantify Γoff and associated change in off‐fault mechanical properties during and after quasi‐static and dynamic rupture. We do so by performing dynamic and quasi‐static shear failure experiments on intact Lanhélin granite under triaxial conditions. We quantify the change in elastic moduli around the fault from time‐resolved 3‐D P wave velocity tomography obtained during and after failure. We measure the off‐fault microfracture damage after failure. From the tomography, we observe a localized maximum 25% drop in P wave velocity around the shear failure interface for both quasi‐static and dynamic failure. Microfracture density data reveal a damage zone width of around 10 mm after quasi‐static failure, and 20 mm after dynamic failure. Microfracture densities obtained from P wave velocity tomography models using an effective medium approach are in good agreement with the measured off‐fault microfracture damage. Γoff obtained from off‐fault microfracture measurements is around 3 kJ m2 for quasi‐static rupture, and 5.5 kJ m2 for dynamic rupture. We argue that rupture velocity determines damage zone width for slip up to a few mm, and that shear fracture energy Γ increases with increasing rupture velocity.

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Variation of Hydraulic Properties Due to Dynamic Fracture Damage: Implications for Fault Zones

Cited by 7 publications

References 91 publications

The competition between fracture nucleation, propagation, and coalescence in dry and water-saturated crystalline rock

The competition between fracture nucleation, propagation, and coalescence in dry and water-saturated crystalline rock

The Effect of Fault Roughness and Earthquake Ruptures on the Evolution and Scaling of Fault Damage Zones

Off‐Fault Damage Characterization During and After Experimental Quasi‐Static and Dynamic Rupture in Crustal Rock From Laboratory P Wave Tomography and Microstructures

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