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.
Highlights
Serpentinite is generated by the hydration of ultramafic rocks and has various mineral compositions depending on temperature–pressure conditions of the MgO–SiO2–H2O system (Evans et al, 2013)
We experimentally investigated the frictional behavior of brucite at various effective normal stresses ranging from 10 to 60 MPa to understand the effect of brucite on the seismic activities at the subduction plate interface in hydrated mantle wedges
The final friction coefficients at a shear displacement of ∼ 20 mm for dry and wet conditions under all normal stress conditions were 0.40 ± 0.04 and 0.26 ± 0.03, respectively (Table 1). These final friction coefficients are mostly independent of the applied normal stress (Fig. 3) and consistent with previous experimental results: 0.38–0.46 and 0.28 for dry and wet brucite, respectively, at an applied normal stress of 100 MPa at room temperature (Moore and Lockner, 2004, 2007)
Summary
Serpentinite is generated by the hydration of ultramafic rocks and has various mineral compositions depending on temperature–pressure conditions of the MgO–SiO2–H2O system (Evans et al, 2013). As serpentinite has been observed in various important tectonic settings and is considered to contribute to the weakness of serpentinite-dominant areas, the frictional properties of serpentinite have been investigated for several decades (see Guillot et al, 2015, and Hirth and Guillot, 2013, for a review). A large volume of serpentinite is located in mantle wedges in which olivine-rich rock of the upper mantle is hydrated by slab-derived water and composes the subduction plate interface, as suggested by geological and seismological studies (Bostock et al, 2002; Christensen, 2004; Guillot and Hattori, 2013; Hyndman and Peacock, 2003; Kawahara et al, 2016; Kawakatsu and Watada, 2007; Mizukami et al, 2014; Peacock and Hyndman, 1999; Reynard, 2013). As slow earthquakes can trigger or be triggered by huge megathrust earthquakes (Obara and Kato, 2016), the nucleation processes of slow earthquakes are important for understanding seismic activities at subduction zones
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