Comparative microstructures of natural and experimentally produced clay-bearing fault gouges

Rutter, E. H.; Maddock, R. H.; Hall, S.; White, S. H.

doi:10.1007/bf00875717

Cited by 391 publications

(235 citation statements)

References 25 publications

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“…Anisotropy of 10-15% is apparent in the compressional wave and shear wave velocities measured through the fault gouge. This anisotropy most likely represents the internal structure of the fault gouge [Rutter et al, 1986]. Anisotropy has also previously been observed in permeability measurements of this fault gouge [Faulkner and Rutter, 1998].…”

Section: 1002/2017gl073726mentioning

confidence: 83%

“…Rock samples were drilled perpendicular and parallel to the foliation of the mica-schist in the laboratory (see Figure 1). The fault gouge displays internal structuring showing P/R 1 foliation, where P foliation is defined by the preferred alignment of phyllosilicates in a plane oblique to the direction of shear and R 1 shears by a sense of obliquity opposite to that of the P foliation [Rutter et al, 1986]. Gouge samples were collected by hammering a copper tube into the fault gouge [e.g., Faulkner and Rutter, 1998].…”

Section: Methodsmentioning

confidence: 99%

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Seismically invisible fault zones: Laboratory insights into imaging faults in anisotropic rocks

Kelly

Faulkner

Rietbrock

2017

Geophysical Research Letters

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Phyllosilicate‐rich rocks which commonly occur within fault zones cause seismic velocity anisotropy. However, anisotropy is not always taken into account in seismic imaging and the extent of the anisotropy is often unknown. Laboratory measurements of the velocity anisotropy of fault zone rocks and gouge from the Carboneras fault zone in SE Spain indicate 10–15% velocity anisotropy in the gouge and 35–50% anisotropy in the mica‐schist protolith. Greater differences in velocity are observed between the fast and slow directions in the mica‐schist rock than between the gouge and the slow direction of the rock. This implies that the orientation of the anisotropy with respect to the fault is key in imaging the fault seismically. For example, for fault‐parallel anisotropy, a significantly greater velocity contrast between fault gouge and rock will occur along the fault than across it, highlighting the importance of considering the foliation orientation in design of seismic experiments.

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Section: 1002/2017gl073726mentioning

confidence: 83%

Section: Methodsmentioning

confidence: 99%

Seismically invisible fault zones: Laboratory insights into imaging faults in anisotropic rocks

Kelly

Faulkner

Rietbrock

2017

Geophysical Research Letters

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“…The fault has an estimated 40 km offset on it and was active throughout the Miocene [Rutter et al, 1986]. Grid references are given in Table 1 for all cores used [Instituto Geogrdfico Nacional, 1985].…”

Section: Sample Collection/characterizationmentioning

confidence: 99%

“…Although Wang et al [1980] did use intact samples, no reference was made to the orientation of the sample relative to the planar fabrics developed within the gouge. Chester et al [1985] pointed out that cataclastic rocks are often well-structured, and this is especially true of phyllosilicate-rich fault rocks, which develop marked composite planar fabrics [Rutter et al, 1986]. These fabrics have been shown to control the permeability anisotropy of natural clay-bearing fault gouges, which can vary by up to 3 orders of magnitude [Faulkner and Rutter, 1998].…”

Section: Introductionmentioning

confidence: 99%

“…If high fluid pressures within faults zones can be maintained by low-permeability fault rocks for significant periods of time, then this will affect the overall strength of the fault zone, perhaps explaining observations such as the apparent low strength of the San Andreas fault system as suggested by the stress/heat flow paradox [Zoback et al, 1987;Lachenbruch and Sass, 1980]. Clay-bearing fault gouges are common constituents of large fault zones [Rutter et al, 1986;Miller, 1996] be present at depth to perhaps 10 km in currently active large faults [Wintsch et al, 1995;Hacker, 1997]. However, owing to their friable nature and tendency to degrade rapidly owing to surface weathering, few experimental studies have been conducted on natural material.…”

Section: Introductionmentioning

confidence: 99%

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Comparisons of water and argon permeability in natural clay‐bearing fault gouge under high pressure at 20°C

Faulkner¹,

Rutter²

2000

J. Geophys. Res.

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182

152

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Abstract. Quantification of fluid transport through fault zones is critical for the understanding of fault mechanics and prediction of subsurface fluid flow. The permeability of clay-bearing fault gouge has been determined using first argon then water as pore fluids under total confining pressures ranging up to 200 MPa and pore pressures of 40 MPa at room temperature. Use of the two pore fluids allows interactions between the gouge and pore fluids to be examined. Natural clay-bearing fault gouge recovered from surface exposures of the Carboneras fault zone in southeastern Spain was used and was collected in such a way that the in situ microstructure was preserved. Cores were collected in directions relative to the well-developed planar fabrics seen in these types of fault rock. The mineralogy of the gouges included muscovite/illite, chlorite, and quartz, with minor amounts of gypsum, albite, and graphite. Glycolation of the gouge showed no discernible amounts of swelling phases. Grain size analyses revealed a bimodal grain size distribution, with the <2 •xm fraction dominant (>50 wt %). This fraction contained predominantly 17 2 22clay phases. Permeabilities in the range of 10-m to 10-m 2 were measured. Experimental results show that the previous highest in situ effective pressure to which the fault gouge had been subjected (overconsolidation pressure) could not be determined from changes in permeability. Differences between water and argon permeabilities determined on the same sample amounted to -•1 order of magnitude, even if the sample had been pressure cycled (reduction to zero and reapplication of both confining and pore pressure) using argon as pore fluid until asymptotic values for permeability had been attained. Volumetric strain measurements showed no enhanced compaction due to the introduction of water as the pore fluid, leading to the conclusion that the reduction in permeability must be due to physicochemical interactions of the water with the fault gouge. The low permeabilities measured support models invoking high fluid pressure weakening of large faults with minimal fluid loss. The stability of structured water films with varying temperature, water pressure and water chemistrv may produce a heterogeneous permeability profile with depth in fault zones.

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Micromechanisms of creep in clay‐rich gouge from the Central Deforming Zone of the San Andreas Fault

French

Chester

2015

JGR Solid Earth

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We report the strength and constitutive behavior of gouge sampled from the Central Deforming Zone (CDZ) of the San Andreas Fault. Layers of flaked CDZ gouge were sheared in the triaxial saw cut configuration using the stress relaxation technique to measure the gouge strength over 4 orders of magnitude in shear strain rate and at rates as low as 5 × 10 −10 s −1 and within an order of magnitude of in situ rates. Deformation conditions correspond to the in situ effective normal stress (100 MPa) and temperature (65 to 120• C) at the sampling depth of 2.7 km. Gouge was sheared dry and with brine pore fluid at 25 MPa pore pressure. Dry gouge is stronger and more rate strengthening than brine-saturated gouge. Brine-saturated CDZ gouge strengthens with increasing strain rate and decreasing temperature, and the dependencies of strength on strain rate and temperature increase at rates below ∼ 5 × 10 −9 s −1 . At strain rates greater than ∼ 5× 10 −9 s −1 , the rate dependence is consistent with previous studies on the CDZ gouge conducted at even higher rates. The increase in rate dependence below ∼ 5× 10 −9 s −1 indicates a change in the rate-controlling deformation mechanism. The magnitude of the friction rate dependence parameter, a, and the temperature sensitivity of a are consistent with crystal plasticity of the phyllosilicates. We hypothesize a micromechanical model for the CDZ gouge whereby a transition from fracture and delamination-accommodated frictional flow to crystal plasticity-accommodated frictional flow occurs with decreasing strain rate.

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Comparative microstructures of natural and experimentally produced clay-bearing fault gouges

Cited by 391 publications

References 25 publications

Seismically invisible fault zones: Laboratory insights into imaging faults in anisotropic rocks

Seismically invisible fault zones: Laboratory insights into imaging faults in anisotropic rocks

Comparisons of water and argon permeability in natural clay‐bearing fault gouge under high pressure at 20°C

Micromechanisms of creep in clay‐rich gouge from the Central Deforming Zone of the San Andreas Fault

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