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

Abstract

AbstractWe 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 (20–600°C) under dry and hydrated conditions. In tests performed on dry solid samples, we observed stable sliding at low temperatures (20–150°C), stick slip at high temperatures (350–600°C), and a transitional “episodic slow slip” behavior at intermediate temperatures (200–300°C). 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 500°C. Our results show a decrease in the rate parameter (a − b) with temperature for both solid and gouge samples; friction transitions from velocity strengthening to velocity weakening at temperature of about 150°C 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.