Spatial Patterns in Frictional Behavior of Sediments Along the Kumano Transect in the Nankai Trough

Okuda, H.; Ikari, Matt J.; Roesner, Alexander; Stanislowski, K.; Hüpers, Andre; Yamaguchi, Asuka; Kopf, Achim J

doi:10.1029/2021jb022546

Cited by 14 publications

(11 citation statements)

References 117 publications

(245 reference statements)

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“…Previous experimental studies have shown that volcanic glass has friction coefficients of 0.6-0.8 at low velocity conditions less than 1 mm/s (Lavallée et al, 2014;Wiemer & Kopf, 2015), consistent with "Byerlee's rule" for rock friction (Byerlee, 1978). When it is mixed with smectite, the frictional strength of the glass-smectite mixture shows an inverse relationship with smectite content (Wiemer & Kopf, 2015), similar to other previous results where weak clay minerals have been mixed with non-clay minerals (Bedford et al, 2022;Ikari et al, 2018;Logan & Rauenzahn, 1987;Okuda et al, 2021;Takahashi et al, 2007;Tembe et al, 2010). At a high slip-velocity up to 1.3 m/s, the frictional strength of volcanic glass is dynamically weakened (Lavallée et al, 2014).…”

Section: Introductionsupporting

confidence: 87%

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

Preprint

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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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Section: Introductionsupporting

confidence: 87%

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

Preprint

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“…The obtained μ showed a landward increasing trend such that it is 0.16-0.35 beneath the outer prism and 0.35-0.44 beneath the inner prism along the plate boundary zone (Figure 6b). Such a landward increasing trend of friction coefficient was also inferred by the Coulomb wedge model combining the prism topography with frictional strength of core samples from the accretionary prism, which did not include any a priori mineralogical variations (Okuda et al, 2021). They proposed that the μ at the trench-ward portion along the plate boundary beneath the outer prism is 0.24 (Ikari et al, 2013), and that the μ increases to 0.5-0.6 near the boundary between the outer and inner prisms, and to 0.6-0.8 at the updip limit depth of seismogenic zone.…”

Section: Spatial Variation In Frictional Strengthmentioning

confidence: 84%

“…Based on these studies, the previous study (Okuda et al, 2021) assumed the λ along the bottom of accretionary prism (=λb) to be 0.5 beneath the prism toe, 0.7 at the trench-ward part beneath the outer prism, 0.9 at the landward part beneath the outer prism, and 0.8 beneath the inner prism. Nearly hydrostatic pore pressure conditions were assumed inside the prism (λ = 0.5).…”

Section: Inference On Pore Pressure Conditionmentioning

confidence: 99%

In-situ frictional behavior of subducting sediment in the shallow Nankai Trough

Okuda¹,

Kitamura²,

Takahashi³

et al. 2023

Preprint

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The transition from smectite to illite at around the depth with temperature of ~150 °C has long been hypothesized as one of controlling factors of the updip limit depth of the seismogenic zone of subduction zones. Although illite has a higher friction coefficient than smectite, previous friction experiments have little reported that the smectite-illite transition accompanies the transition from velocity strengthening (not seismogenic) to velocity weakening (potentially seismogenic). In this study, we simulated in-situ temperature-pressure-mineral conditions along the shallow plate boundary in the Nankai Trough, and conducted friction experiments to further constrain the role of smectite-illite transition in seismogenesis in subduction zones. We found that friction coefficient of the simulated sediment increased with the progress of illitization and followed the Reuss average of friction coefficients of the mineral phases. The obtained friction coefficients and the Coulomb wedge model inferred that the pore pressure conditions around the plate boundary may be over-pressured but not as high as lithostatic pressure. Higher friction coefficients of sediment due to diagenetic processes will be required to sustain the nearly lithostatic pore pressure along the plate boundary. The velocity dependence of friction coefficient (a−b) was always positive except under the velocity conditions lower than ~10 μm/s at 171 °C. Therefore, the shallow slow earthquakes beneath the outer prism cannot be explained only by the frictional instability of unconsolidated sediment. Since the smectite-illite transition mostly completes at ~30 km landward from the trough axis, the transition from velocity strengthening to velocity weakening observed at 171 °C is caused by temperature-dependent frictional behavior of illite-rich material. Hence the updip limit depth of the seismogenic zone of subduction zones would be mainly controlled by frictional properties of illite-rich material.

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“…Despite the clay-rich nature of the Nankai Trough sediments, velocity-weakening friction has been observed in other friction studies testing materials from this subduction zone, and specifically from the modern outer accretionary prism (Tsutsumi et al 2011;Roesner et al 2020;Okuda et al 2021). Although an earlier study found only velocity-strengthening friction for the megasplay (Ikari and Saffer 2011), this was later attributed to testing at higher than in situ stresses (Roesner et al 2020).…”

Section: Mechanisms Of Observed Behavior and Comparison With Previous...mentioning

confidence: 86%

Weakening behavior of the shallow megasplay fault in the Nankai subduction zone

Roesner

Ikari

Hüpers

et al. 2022

Earth Planets Space

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The Nankai Trough megasplay fault hosts diverse modes of fault slip, ranging from slow slip events to megathrust earthquakes, and is responsible for related phenomena such as tsunamis and submarine landslides. All types of slip events require some kind of frictional weakening process in order to nucleate and propagate. We tested fluid-saturated, powdered megasplay fault samples in a direct shear apparatus under effective normal stresses of 2–18 MPa to investigate their friction velocity- and slip-dependence. The experiments show that for short distances (1 mm) after a velocity step, there is an evolution from velocity weakening at low effective normal stress to velocity strengthening at high effective normal stresses. Over a longer distance (5 mm), large velocity weakening is observed over all tested effective normal stresses. In all experiments, slip weakening behavior occurred with relatively large weakening rates at low effective normal stresses and smaller weakening rates at higher effective normal stresses. Critical stiffnesses for slip instability were calculated for both the velocity and slip dependence of friction to determine their relative importance. At shallow depths, velocity weakening would be the main cause of frictional instability for both small and large slip perturbations, whereas at greater depth instability requires either slip weakening over small slip distances, or velocity weakening induced by larger slip. Regardless of the underlying mechanism, the observed slip instability at lower effective stresses increases the likelihood for fault slip events to travel to the seafloor which may cause submarine landslides and tsunamis. Graphical Abstract

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Spatial Patterns in Frictional Behavior of Sediments Along the Kumano Transect in the Nankai Trough

Abstract: Megathrust earthquakes at subduction margins induce hazardous ground motion and tsunami. The Nankai Trough, where the Philippine Sea plate subducts beneath the Amurian microplate offshore SW Japan at a convergence rate of 4.0-6.0 cm/yr (

Cited by 14 publications

References 117 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

In-situ frictional behavior of subducting sediment in the shallow Nankai Trough

Weakening behavior of the shallow megasplay fault in the Nankai subduction zone

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