Frictional properties of the active San Andreas Fault at SAFOD: Implications for fault strength and slip behavior

Carpenter, B. M.; Saffer, D. M.; Marone, Chris

doi:10.1002/2015jb011963

Cited by 104 publications

(86 citation statements)

References 80 publications

(157 reference statements)

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“…Slip parallel to aligned phyllosilicates would not change contact area during slip following a rate‐step, and would therefore not show an evolution of friction during subsequent slip (Ikari et al, ). This has been observed previously in biaxial experiments on phyllosilicate‐rich rocks, including illite schists, chloritic schists, and montmorillonite‐quartz mixtures (Ikari et al, ) as well as smectite‐rich samples (Carpenter et al, ; Saffer & Marone, ), and our results show the same behavior at 150 °C as documented in these earlier room‐temperature experiments (Figures b–d).…”

Section: Interpretationssupporting

confidence: 92%

Frictional Strengths of Subduction Thrust Rocks in the Region of Shallow Slow Earthquakes

et al. 2020

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Earthquakes are expected to nucleate within velocity‐weakening materials; however, at the updip limit of the subduction seismogenic zone, the principal lithologies exhibit velocity‐strengthening behavior. At an exhumed analogue for present‐day subduction at Nankai (the Mugi Mélange, Japan) two examples of paleoseismic features occur within altered basalts, suggesting that they may be velocity‐weakening. We shear altered basalt and shale matrix from the mélange in the triaxial saw cut configuration at in situ conditions of deformation (Pc = 120 MPa, T = 150 °C) for two pore fluid factors (λ = 0.36, 0.7). The shale matrix exhibits a coefficient of friction between 0.4 and 0.5, and velocity‐strengthening behavior. Altered basalt exhibits Byerlee friction and velocity‐weakening behavior. In most experiments deformation was partitioned into Riedel shears, which have a lower percentage of clasts, clast size distributions with higher fractal dimensions, and shape factors indicating rounder clasts compared to the matrix between Riedel shears. We hypothesize that earthquakes preferentially nucleate within altered basalt at the updip limit of the seismogenic zone. More complex forms of deformation (e.g., shallow very low frequency earthquakes) may occur by mixing velocity‐weakening altered basalt into the velocity‐strengthening shale matrix. In subduction zones where the matrix is composed of shale, this complex behavior is limited to shallow depths (T < ~250 °C), above the updip transition to velocity‐weakening behavior for the matrix. Altered basalt is a ubiquitous subducting material, and future studies on its behavior through a range of subduction zone conditions are required for a full understanding of the mechanical behavior of subduction zones.

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Section: Interpretationssupporting

confidence: 92%

Frictional Strengths of Subduction Thrust Rocks in the Region of Shallow Slow Earthquakes

et al. 2020

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“…Low friction coefficients have also been widely reported in natural faults, including 0.1-0.2 for fault gouge in the San Andreas fault (Carpenter et al 2015) and 0.3 for fault gouge in the Taiwan Chelungpu fault (Mizoguchi et al 2008). The low values in the fault gouges of the Atera fault could be ascribed to the presence of large amounts of clay minerals.…”

Section: Discussionmentioning

confidence: 97%

Heterogeneity in friction strength of an active fault by incorporation of fragments of the surrounding host rock

Kato

Hirono

2016

Earth Planet Sp

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To understand the correlation between the mesoscale structure and the frictional strength of an active fault, we performed a field investigation of the Atera fault at Tase, central Japan, and made laboratory-based determinations of its mineral assemblages and friction coefficients. The fault zone contains a light gray fault gouge, a brown fault gouge, and a black fault breccia. Samples of the two gouges contained large amounts of clay minerals such as smectite and had low friction coefficients of approximately 0.2-0.4 under the condition of 0.01 m s −1 slip velocity and 0.5-2.5 MP confining pressure, whereas the breccia contained large amounts of angular quartz and feldspar and had a friction coefficient of 0.7 under the same condition. Because the fault breccia closely resembles the granitic rock of the hangingwall in composition, texture, and friction coefficient, we interpret the breccia as having originated from this protolith. If the mechanical incorporation of wall rocks of high friction coefficient into fault zones is widespread at the mesoscale, it causes the heterogeneity in friction strength of fault zones and might contribute to the evolution of fault-zone architectures.

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“…In terms of frictional strength, kaoliniterich samples have shown diverse values ranging between 0.22 to 0.55 and 0.4 to 0.85 for wet and dry conditions, respectively Brantut et al, 2008;Carpenter et al, 2016Carpenter et al, , 2015Crawford et al, 2008;Fang et al, 2017;Moore & Lockner, 2004;Morrow et al, 2000). Moreover, while results on the frictional strength of kaolinite-rich gouges are more common, data on the velocity dependence of friction and fault healing are limited.…”

Section: Introductionmentioning

confidence: 99%

Frictional Properties of Opalinus Clay: Implications for Nuclear Waste Storage

et al. 2018

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The kaolinite‐bearing Opalinus Clay (OPA) is the host rock proposed in Switzerland for disposal of radioactive waste. However, the presence of tectonic faults intersecting the OPA formation put the long‐term safety performance of the underground repository into question due to the possibility of earthquakes triggered by fault instability. In this paper, we study the frictional properties of the OPA shale. To do that, we have carried out biaxial direct shear experiments under conditions typical of nuclear waste storage. We have performed velocity steps (1–300 μm/s) and slide‐hold‐slide tests (1–3,000 s) on simulated fault gouge at different normal stresses (4–30 MPa). To establish the deformation mechanisms, we have analyzed the microstructures of the sheared samples through scanning electron microscopy. Our results show that peak (μpeak) and steady state friction (μss) range from 0.21 to 0.52 and 0.14 to 0.39, respectively, thus suggesting that OPA fault gouges are weak. The velocity dependence of friction indicates a velocity strengthening regime, with the friction rate parameter (a − b) that decreases with normal stress. Finally, the zero healing values imply a lack of restrengthening during interseismic periods. Taken together, if OPA fault reactivates, our experimental evidence favors an aseismic slip behavior, making the nucleation of earthquakes difficult, and long‐term weakness, resulting in stable fault creeping over geological times. Based on the results, our study confirms the seismic safety of the OPA formation for a nuclear waste repository.

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Frictional properties of the active San Andreas Fault at SAFOD: Implications for fault strength and slip behavior

Cited by 104 publications

References 80 publications

Frictional Strengths of Subduction Thrust Rocks in the Region of Shallow Slow Earthquakes

Frictional Strengths of Subduction Thrust Rocks in the Region of Shallow Slow Earthquakes

Heterogeneity in friction strength of an active fault by incorporation of fragments of the surrounding host rock

Frictional Properties of Opalinus Clay: Implications for Nuclear Waste Storage

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