Frictional melting of gabbro under extreme experimental conditions of normal stress, acceleration, and sliding velocity

With the advent of high‐velocity shear apparatus, several experimental studies have performed in recent years, improving our understanding of the evolution of fault during seismic slip. However, these experiments were conducted under relatively normal stress (<20 MPa) and using small cylindrical samples where a large gradient in velocity exists across the sliding surface. Given the above limitations, the extrapolation these experimental results to natural conditions is not trivial. Here we present results an experimental study on gabbroic rocks using a newly developed rotary shear capable of reaching higher normal stress (up to 50 MPa) on ring‐shaped samples (30/50 mm internal/external diameter) and allowing precise control of the imposed slip function. The results confirm that steady state shear stress during the melt‐lubricated of the experiment depends on normal stress in the form of a power law equation as by theoretical models. However, the exponent appears closer to 0.5, contrary to the prediction of 0.25. We observe no systematic dependence of shear stress on , but increasing deceleration drastically decreases the recovery of friction during slip. We find that the slip‐weakening distance decreases inversely with increasing stress, in agreement with theoretical considerations, and decreases with increasing rate. Extrapolation of the slip‐weakening distance to natural conditions predicts a slip for ancient seismic events of 0.3–1 m/s when compared with field estimates. These compare well with seismological estimates.