Frictional properties of gabbro at conditions corresponding to slow slip events in subduction zones

Abstract

We conducted a series of experiments to explore the rate and state frictional properties of gabbro at conditions thought to be representative of slow slip events (SSEs) in subduction zones. The experiments were conducted using a heated direct shear apparatus. We tested both solid and simulated gouge samples at low effective normal stress (5-30 MPa) over a broad range of temperatures (20-6008C) under dry and hydrated conditions. In tests performed on dry solid samples, we observed stable sliding at low temperatures (20-1508C), stick slip at high temperatures (350-6008C), and a transitional ''episodic slow slip'' behavior at intermediate temperatures (200-3008C). In tests performed on dry gouge samples, we observed stable sliding at all temperatures. Under hydrated conditions, the gouge samples exhibited episodic slow slip and stick-slip behavior at temperatures between 300 and 5008C. Our results show a decrease in the rate parameter (a 2 b) with temperature for both solid and gouge samples; friction transitions from velocity strengthening to velocity weakening at temperature of about 1508C for both solid and gouge samples. We do not observe transition to velocity-strengthening friction at the high end of the tested temperature range. Our results suggest that the occurrence of slow slip events and the downdip limit of the seismogenic zone on subduction megathrusts cannot be solely explained by the temperature dependence of frictional properties of gabbro. Further experimental studies are needed to evaluate the effects of water fugacity and compositional heterogeneity (e.g., the presence of phyllosilicates) on frictional stability of subduction megathrusts.

Velocity‐weakening behavior of Westerly granite at temperature up to 600°C

“…Recent high‐temperature triaxial tests on gabbroic gouge indicated velocity‐weakening behavior up to 600°C [ He et al , ]. Direct shear experiments on gabbro at conditions analogous to those in this study also show a progressive decrease in the rate parameter ( a − b ) with temperature, with a transition to velocity weakening above 150°C for bare surfaces, and 300°C for thick gouges [ Mitchell et al , ]. These findings, along with results presented in this study, imply that the middle and lower continental crust can be seismically active under certain conditions.…”

“…Consideration of evolution laws that are more complex compared to equations and [e.g., Kato and Tullis , ; Nagata et al , ] did not result in improvements of model fit to the data [ Mitchell et al , ], and therefore here we present only results corresponding to the aging law and the slip law. The relationship between the stressing rate and the rate of stretching of a thick metal bar (analog of a spring) that connects the stepper motor to the specimen holder follows from the Hooke's law and is given by where k is the effective rigidity (spring constant) and V ∗ is the load point velocity.…”

Dependence of seismic coupling on normal fault style along the Northern Mid‐Atlantic Ridge

“…Experiments on wet gabbro gouges [He et al, 2007;Mitchell et al, 2015] indicate velocity-strengthening behavior at low temperatures (<200ºC) across a wide range of pressures. A narrow range of temperatures (~200-300ºC) enables velocity-weakening behavior at high effective pressures (~200 MPa).…”

Apparent Dependence of Rate- and State-Dependent Friction Parameters on Loading Velocity and Cumulative Displacement Inferred from Large-Scale Biaxial Friction Experiments

“…The RSF parameters can be estimated also from stick-slip behaviors (Mitchell et al 2015). Mitchell et al (2015) performed the inversions of experimental data for unstable sliding using a spring-slider model, but they ignored the inertia in their numerical simulations [see their Eq.…”

“…The RSF parameters can be estimated also from stick-slip behaviors (Mitchell et al 2015). Mitchell et al (2015) performed the inversions of experimental data for unstable sliding using a spring-slider model, but they ignored the inertia in their numerical simulations [see their Eq. (7)], which may lead to inaccurate estimation of the RSF parameters because in the quasi-static system, finite amplitude periodic oscillations are observed for very limited parameters and the slip velocity becomes infinite in unstable sliding regimes (Gu et al 1984) where the inertia makes the slip and stress evolution completely different (Rice and Tse 1986).…”