Weakening of quartz rocks at subseismic slip rates due to frictional heating, but not to lubrication by wear materials of hydrated amorphous silica or silica gel

Kanagawa, Kyuichi; Murayama, Hiroki; Sugita, Asuka; Takahashi, Miki; Sawai, Michiyo; Furukawa, Noboru; Hirose, Takehiro

doi:10.1016/j.tecto.2020.228429

Cited by 6 publications

(3 citation statements)

References 34 publications

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“…These results are different from what is observed for quartz‐rich rocks, which often shows a reduction in frictional strength at intermediate slip velocities due to silica‐gel lubrication or the formation of amorphous wear materials (Di Toro et al., 2004; Goldsby & Tullis, 2002; Hayashi & Tsutsumi, 2010; Rowe et al., 2019). This study supports the idea that thermal processes are important for dynamic weakening and that the preexisting amorphous grains themselves do not induce the weakening (Kanagawa et al., 2020). Although the FEM modeling of the single‐ V test could not estimate the T condition inside the gouge, because the measured T was lower than in the multi‐ V test, we speculate that the dynamic weakening in the single‐ V test may instead be caused by flash heating or thermal pressurization, rather than vaporization.…”

Section: Discussionsupporting

confidence: 89%

Potential Role of Volcanic Glass‐Smectite Mixtures in Slow Earthquakes in Shallow Subduction Zones: Insights From Low‐ to High‐Velocity Friction Experiments

2023

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Volcanic glass and its mixture with smectite are commonly observed in shallow parts of subduction zones. As volcanic glass layers often act as glide planes in submarine landslides, and because its alteration product, smectite, is one of the frictionally weakest geological materials, the frictional characteristics of volcanic glass‐smectite mixtures are important for fault slip behavior in shallow parts of subduction zones. We performed a series of friction experiments on volcanic glass‐smectite mixtures with different smectite contents from 0% to 100% at various velocity conditions from 10 μm/s to 1 m/s under an effective normal stress of 5 MPa and pore pressure of 10 MPa. In general, apparent friction coefficients negatively depend on the smectite content at any velocity tested. We found that samples with smectite contents of 15%–30% showed a drastic slip‐weakening behavior at intermediate velocities of 1–3 mm/s. Finite element method modeling shows that thermal pressurization does not contribute to the observed weakening behavior. The critical nucleation length estimated from the slip‐weakening behavior is approximately 1–10 km, which is large enough to prevent the slip to accelerate to seismic slip velocity. Therefore, gouges with minor amount of clay, such as subducting volcanic ash layers, may contribute to the occurrence of the slow earthquakes at shallow depths in subduction zones.

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Section: Discussionsupporting

confidence: 89%

Potential Role of Volcanic Glass‐Smectite Mixtures in Slow Earthquakes in Shallow Subduction Zones: Insights From Low‐ to High‐Velocity Friction Experiments

2023

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“…In addition, because the dynamic weakening in the 100% glass sample occurred just after the maximum T within the gouge reached the boiling T of 311℃ for water with 10 MPa (Figure 7c), the observed dynamic weakening in the multi-V test may be caused by vaporization of the pore water (Acosta et al, 2018;Chen et al, 2017;Hunfeld et al, 2021). This result supports the idea that thermal processes are important for dynamic weakening and that the amorphous grains themselves do not induce the weakening (Kanagawa et al, 2020). Although the FEM modeling of the single-V test could not estimate the T condition inside the gouge, because the measured T was lower than in the multi-V test, the dynamic weakening in the single-V test may instead be caused by flash heating or thermal pressurization, rather than vaporization.…”

Section: Dynamic Weakening For 100% Glass Caused By Thermal Processessupporting

confidence: 68%

Potential role of volcanic glass-smectite mixtures in slow earthquakes in shallow subduction zones: Insights from low- to high-velocity friction experiments

Okuda

Hirose

Yamaguchi

2022

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Volcanic glass and its mixture with smectite are commonly observed in shallow parts of subduction zones. As volcanic glass layers often act as a glide plane to induce mass transportation such as submarine landslides, and because its alteration product, smectite, is one of the frictionally weakest geological materials, the frictional characteristics of volcanic glass-smectite mixtures are important for fault slip behavior in shallow parts of subduction zones. We performed a series of friction experiments on volcanic glass-smectite mixtures with different smectite contents at various velocity conditions from 10 μm/s to 1 m/s under an effective normal stress of 5 MPa and pore pressure of 10 MPa. In general, friction coefficients negatively depend on the smectite content at any velocity tested. We found that samples with smectite contents of 15-30 % showed a drastic slip-weakening behavior at intermediate velocities of 1-3 mm/s with a characteristic slip displacement of ~0.1 m. Finite element method modeling shows that thermal pressurization does not contribute to the observed weakening behavior. We propose that gouge fluidization or compaction-induced pore pressure increase may be the cause of the weakening. The slip-weakening behavior at intermediate velocities enlarges a critical nucleation length for frictional instability to 1-30 km, or prevent acceleration to seismic slip velocities. Therefore, gouges with minor amount of clay, such as subducting volcanic ash layers, may contribute to the occurrence of the at shallow depths in subduction zones.

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“…These amorphous silica-related lubrication in LSZ may explain the observed decrease in shear stress during our experiments. On the other hand, Kanagawa et al (2020) recently suggested that not hydration of amorphous silica (formation of silica gel) but frictional heating can be responsible for the decrease in the friction coefficient during their rotary-shear friction experiments using quartz-bearing agate gouges. This mechanism is, however, unlikely to explain a gradual weakening of our quartz gouges as we observed no significant temperature increase during the experiments at 0.001 m s −1 using quartz ( Figure S10).…”

Section: 1029/2020jb019956mentioning

confidence: 99%

Mechanical Amorphization of Synthetic Fault Gouges During Rotary‐Shear Friction Experiments at Subseismic to Seismic Slip Velocities

et al. 2020

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Although the effects of mechanical amorphization by fault motion on fault rocks have been investigated both in nature and experiments, the relationship between slip processes and the amount of amorphous materials produced remains unclear. We performed rotary-shear friction experiments on synthetic quartz and kaolinite gouges at room temperature, normal stresses of 1 or 3 MPa, slip velocities of 0.001 or 1 m s −1 , and displacements of 1-101 m. X-ray diffraction and microscopic observation data revealed that mechanical amorphization in both materials was accompanied by grain-size reduction, particle rounding, and the formation of ultrafine particles. The amount of amorphous materials produced was strongly dependent on mineralogy and total frictional work regardless of slip velocity. Therefore, mechanical amorphization can occur during both coseismic and subseismic slip. Amorphization of~7 wt% of quartz gouge required 30.33 MJ kg −1 of frictional work, whereas for kaolinite gouge, only 0.77 MJ kg −1 was required, which is consistent with observed preferential amorphization of clay minerals in faults. For kaolinite, up to 6% of frictional work can be used for mechanical amorphization, indicating its potential importance for faulting energetics. Because some kinds of amorphous phyllosilicates release water at lower temperature than crystalline, mechanical amorphization of fault rocks may influence thermochemical pressurization. Gradual weakening of quartz gouge at 0.001 m s −1 slip velocity suggested that <4 wt% of amorphous silica can weaken a fault by amorphous silica-related lubrication. Mechanical amorphization may accelerate pressure solution healing of faults if dissolution can occur under high porous conditions.

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Weakening of quartz rocks at subseismic slip rates due to frictional heating, but not to lubrication by wear materials of hydrated amorphous silica or silica gel

Cited by 6 publications

References 34 publications

Potential Role of Volcanic Glass‐Smectite Mixtures in Slow Earthquakes in Shallow Subduction Zones: Insights From Low‐ to High‐Velocity Friction Experiments

Potential Role of Volcanic Glass‐Smectite Mixtures in Slow Earthquakes in Shallow Subduction Zones: Insights From Low‐ to High‐Velocity Friction Experiments

Potential role of volcanic glass-smectite mixtures in slow earthquakes in shallow subduction zones: Insights from low- to high-velocity friction experiments

Mechanical Amorphization of Synthetic Fault Gouges During Rotary‐Shear Friction Experiments at Subseismic to Seismic Slip Velocities

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