Effect of normal stress on the frictional behavior of brucite: application to slow earthquakes at the subduction plate interface in the mantle wedge

Abstract

Abstract. We report the results of friction experiments on brucite under both dry and wet conditions under various normal stresses (10–60 MPa). The final friction coefficients of brucite were determined to be 0.40 and 0.26 for the dry and wet cases, respectively, independent of the normal stress. Under dry conditions, velocity-weakening behavior was observed in all experiments at various normal stresses. Under wet conditions, velocity weakening was observed at low normal stress (10 and 20 MPa), whereas velocity strengthening was determined at a higher applied normal stress. Microstructural observations of recovered experimental samples indicate localized deformation within a narrow shear band, implying that a small volume of brucite can control the bulk frictional strength in an ultramafic setting. Among serpentinite-related minerals, weak and unstable frictional behavior of brucite under hydrated mantle wedge conditions may play a role in slow earthquakes at the subduction plate interface in the mantle wedge.

Atomic-scale interlayer friction of gibbsite is lower than brucite due to interactions of hydroxyls

“…However, an additional frictional mechanism will be required to fully explain the difference in μ g . Most interlayer macroscopic frictions μ M are lower than the gouge friction μ g as reported for brucite (Okuda et al 2019(Okuda et al , 2021a, pyrophyllite (Moore and Lockner 2004;Sakuma et al 2020), muscovite (Kawai et al 2015;Sakuma et al 2018), and montmorillonite (Sakuma et al 2022). Mohs hardness may be related to μ g (Moore and Lockner 2004), although our data is insufficient to test their relationship.…”

“…Gibbsite (Al(OH) 3 ) has a similar crystal structure as that of brucite (Mg(OH) 2 ), which was studied in OKS19. Experimentally obtained friction coefficients of the gouges of gibbsite and brucite were quite different; the value for gibbsite is 0.74, whereas that for brucite is 0.39 (Moore and Lockner 2004;Okuda et al 2021a). To evaluate their interlayer frictional properties and their roles in their single-crystal and gouge friction coefficients, herein, we discuss the difference in friction coefficients of gibbsite and…”

Hydrothermal Friction Experiments on Simulated Basaltic Fault Gouge and Implications for Megathrust Earthquakes

“…It is important to note here that, both a decrease in σ n eff and/or an increase in P f do not influence the ( a−b ) value of altered basalt at T = 200°C unlike blueschist, actinolite‐chlorite mixture, and other materials (Bedford et al., 2021; Okamoto et al., 2020; Okuda et al., 2021; Sawai et al., 2016). Such an over‐pressured condition possibly induces a slower slip because the nucleation size L c , defined as follows (Dieterich, 1986): $$$\begin{array}{c}{L}_{c}=\frac{\xi G}{{K}_{c}}=\frac{\xi G{d}_{c}}{(b-a){\sigma }_{n}^{eff}},\end{array}$$$ where ξ is a geometric constant of order 1 and G is the shear modulus of surrounding rock, becomes large.…”

“…It is important to note here that, both a decrease in σ n eff and/or an increase in P f do not influence the (a−b) value of altered basalt at T = 200°C unlike blueschist, actinolite-chlorite mixture, and other materials (Bedford et al, 2021;Okamoto et al, 2020;Okuda et al, 2021;Sawai et al, 2016). Such an over-pressured condition possibly induces a slower slip because the nucleation size L c , defined as follows (Dieterich, 1986):…”