Depth profile of frictional properties in the inner Nankai accretionary prism using cuttings from IODP Site C0002

Fujioka, Riho; Katayama, Ikuo; Kitamura, Mitsutaka; Okuda, H.; Hirose, Takehiro

doi:10.1186/s40645-022-00488-1

Cited by 4 publications

(3 citation statements)

References 63 publications

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“…For smectite, (a−b) decreases with effective normal stress of up to 70 MPa (Mizutani et al, 2017;Morrow et al, 2017). Sediment samples from the Nankai Trough and illite-rich shale showed a positive trend on (a−b) with respect to a reduction in effective normal stress and an increase in pore pressure (Bedford et al, 2021;Fujioka et al, 2022;den Hartog & Spiers, 2013). All those studies suggest that sediments may be frictionally stable at the in-situ temperature-pressure-mineral conditions in the shallow part of the Nankai accretionary prism.…”

Section: Implications For Seismic Activities In the Shallow Nankai Tr...mentioning

confidence: 90%

“…The slope angles of seafloor (α) are 4° and 0.1° for the outer and inner prisms. The μ of sediment within the outer prism (μw) was assumed to be 0.30-0.55 and that within the inner prism was 0.45-0.60 based on friction studies on the drilled samples from each prism (Fujioka et al, 2022;Okuda et al, 2021). From those μ values along the underthrust sediment and the prism sediments, the λb can be evaluated by following equations of the Coulomb wedge model (Dahlen, 1990):…”

Section: Inference On Pore Pressure Conditionmentioning

confidence: 99%

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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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Section: Implications For Seismic Activities In the Shallow Nankai Tr...mentioning

confidence: 90%

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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“…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). Other recent studies testing deeper (km-scale) material from the older, inner accretionary prism have shown consistent velocity-strengthening friction (Bedford et al 2021;Fujioka et al 2022), highlighting potentially fundamentally different behavior between the outer and inner prisms that may explain large-scale deformation behavior of the Nankai margin (Kimura et al 2007). Roesner et al (2020) noted that velocity-weakening in the megasplay samples showed larger values of the rate-and-state parameter b, and based on a microphysical explanation for rate-and-state frictional behavior (e.g., Dieterich and Kilgore 1994) suggested that the velocity weakening is somehow related to differences in the real area of contact as a function of effective normal stress.…”

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

confidence: 98%

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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