Influence of Grain‐Scale Properties on Localization Patterns and Slip Weakening Within Dense Granular Fault Gouges

Casas, Nathalie; Mollon, Guilhem; Daouadji, Ali

doi:10.1029/2022jb025666

Cited by 7 publications

(4 citation statements)

References 174 publications

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“…Moreover, the fabrics of the gouge samples differ characteristically for the various gouge frictional responses (velocity‐strengthening vs. velocity‐weakening) as apparent in the microstructures. Among them, grain size reduction in a localized shear zone appears to control the velocity‐weakening behavior, and instability (Casas et al., 2023; Zhang & He, 2016). However, our experimental results show that the feldspar gouge exhibits velocity‐weakening behavior at P f = 90 MPa, with few distinct R1 shear zones observed in the microstructures, rather, exhibiting regular shear fragmentation.…”

Section: Discussionmentioning

confidence: 99%

Frictional Properties of Feldspar‐Chlorite Gouges and Implications for Fault Reactivation in Hydrothermal Systems

Hu,

Zhang,

Zhang

et al. 2024

Earth and Space Science

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As a particularly common mineral in granites, the presence of feldspar and feldspar‐chlorite gouges at hydrothermal conditions has important implications in fault strength and reactivation. We present laboratory observations of frictional strength and stability of feldspar (K‐feldspar and albite) and feldspar‐chlorite gouges under conditions representative of deep geothermal reservoirs to evaluate the impact on fault stability. Velocity‐stepping experiments are performed at a confining stress of 95 MPa, pore pressures of 35–90 MPa, and temperatures of 120–400°C representative of in situ conditions for such reservoirs. Our experiment results indicate that the feldspar gouge exhibits strong friction (μ ∼ 0.71) at all experimental temperatures (∼120–400°C) but when T > 120°C, the frictional response transitions from velocity‐strengthening to slightly velocity‐weakening. At constant confining pressure and temperature, increasing the pore pressure increases the friction coefficient (∼0.70–0.85) and the gouge remains slightly velocity weakening. The presence of alteration‐sourced chlorite leads to a transition from velocity weakening to velocity strengthening in the mixed gouge at experimental temperatures and pore pressures. As a ubiquitous mineral in reservoir rocks, feldspar is shown to potentially contribute to unstable sliding over ranges in temperature and pressure typical in deep hydrothermal reservoirs. These findings emphasize that feldspar minerals may increase the potential for injection‐induced seismicity on pre‐existing faults if devoid of chloritization.

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Section: Discussionmentioning

confidence: 99%

Frictional Properties of Feldspar‐Chlorite Gouges and Implications for Fault Reactivation in Hydrothermal Systems

Hu,

Zhang,

Zhang

et al. 2024

Earth and Space Science

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“…A decrease of the Rate-and-State Friction parameters (a-b) and D c (both rendering the fault more prone to unstable sliding) was systematically observed, in particular during the initial rapid build up of the gouge layer. This was however related to the development of localization patterns (R1-bands and Y-bands, see Casas et al, 2023), and these are features that cannot be captured in our model because our grains are too large and we do not simulate comminution. Our findings however enrich this picture by indicating that the rate of gouge thickening is variable in space, and that the local evolution of the fault toward instability depicted in Noël et al (2023) is certainly prone to the same spatial variability.…”

Section: Fault Evolutionmentioning

confidence: 94%

“…A good way to observe the emergence of complexity is to perform laboratory earthquakes in controlled conditions, starting from a homogeneous initial state, and to monitor the spontaneous development of seismic cycles (Aubry et al., 2020; Bayart et al., 2018; Bolton et al., 2020; Dresen et al., 2020; Goebel et al., 2013; Guérin‐Marthe et al., 2023; Kandula et al., 2019; Leeman et al., 2016; Li & Zhou, 2021; Marty et al., 2019; McLaskey, 2019; Passelègue et al., 2016; Scuderi et al., 2017; Sobolev et al., 1996; Xu et al., 2019). This can be nicely complemented by numerical simulations, provided that they are able to reproduce the main physics at stake, which include rock elastodynamics, damage mechanics, and granular physics (Casas et al., 2022, 2023; Dorostkar et al., 2017; Guo & Morgan, 2007; Mair et al., 2002; Mollon et al., 2021; Morgan & Boettcher, 1999; Papachristos et al., 2023; Taboada & Renouf, 2023; Wang et al., 2019). In the present paper, we revisit numerical data originating from a set of simulations described in details in Mollon et al.…”

Section: Introductionmentioning

confidence: 99%

Laboratory Earthquakes Simulations—Emergence, Structure, and Evolution of Fault Heterogeneity

Mollon,

Aubry,

Schubnel

2024

JGR Solid Earth

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Seismic faults are known to exhibit a high level of spatial and temporal complexity, and the causes and consequences of this complexity have been the topic of numerous research works in the past decade. In this paper, we investigate the origins and the structure of this complexity by considering a numerical model of laboratory earthquake experiment, where we introduce a fault with homogeneous mechanical properties but allow it to evolve spontaneously to its natural level of complexity. This is achieved by coupling the elastic deformability of the off‐fault medium (and therefore allowing for heterogeneous stress fields to develop) and the discrete degradation and gouge formation at the fault plane (and therefore allowing for structural heterogeneity to develop). Numerical results show the development of persistent stress, damage, and gouge thickness heterogeneities, with a much larger variability in space than in time. Strong positive correlations are found between these quantities, which suggest a positive feedback between local normal stress and damage rate, only mildly mitigated by the mobility of the granular gouge in the interface. For a wide range of confining stresses, after a sufficient number of seismic cycles, the fault reaches a state of established disorder with a constant roughness, a certain amount of periodicity at the millimetric scale, and a power law decay of the Power Spectral Density at smaller spatial scales. The typical height‐to‐wavelength ratio of geometrical asperities and the correlations between stress and damage profiles are in good agreement with previous field or lab estimates.

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“…The fabrics of the gouge samples differ characteristically for the various gouge frictional responses (velocity-strengthening / velocity-weakening). Among them, grain size reduction appears to control the velocity-weakening behavior, and instability (Zhang et al, 2016;Casas et al, 2023). The microstructures of the deformed gouges are illustrated in Figures 9-10.…”

Section: Microstructural Observationsmentioning

confidence: 99%

Frictional Properties of Feldspar-chlorite Altered Gouges and Implications for Fault Reactivation in Hydrothermal Systems

Hu,

Zhang,

Zhang

et al. 2023

Preprint

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As a particularly common minerals in granites, the presence of feldspar and altered feldspar-chlorite gouges at hydrothermal conditions have important implications in fault strength and reactivation. We present laboratory observations of frictional strength and stability of feldspar (K-feldspar and albite) and altered feldspar-chlorite gouges under conditions representative of deep geothermal reservoirs to evaluate the impact on fault stability. Velocity‐ stepping experiments are performed at a confining stress of 95 MPa, pore pressures of 35-90 MPa and temperatures of 120-400°C representative of in situ conditions for such reservoirs. Our experiment results show that the feldspar gouge is frictionally strong (μ~0.71) at all experimental temperatures (~120-400℃) but transits from velocity-strengthening to velocity-weakening at T>120°C. Increasing the pore pressure increases the friction coefficient (~0.70-0.87) and the gouge remains velocity weakening, but this weakening decreases as pore pressures increase. The presence of alteration-sourced chlorite leads to a transition from velocity weakening to velocity strengthening in the mixed gouge at experimental temperatures and pore pressures. As a ubiquitous mineral in reservoir rocks, feldspar is shown to potentially contribute to unstable sliding over ranges in temperature and pressure typical in deep hydrothermal reservoirs. These findings emphasize that feldspar minerals may increase the potential for injection-induced seismicity on pre-existing faults if devoid of chlorite alteration.

show abstract

Influence of Grain‐Scale Properties on Localization Patterns and Slip Weakening Within Dense Granular Fault Gouges

Cited by 7 publications

References 174 publications

Frictional Properties of Feldspar‐Chlorite Gouges and Implications for Fault Reactivation in Hydrothermal Systems

Frictional Properties of Feldspar‐Chlorite Gouges and Implications for Fault Reactivation in Hydrothermal Systems

Laboratory Earthquakes Simulations—Emergence, Structure, and Evolution of Fault Heterogeneity

Frictional Properties of Feldspar-chlorite Altered Gouges and Implications for Fault Reactivation in Hydrothermal Systems

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