Examination of multi-scale flash-heating at seismic slip rates in granite

Monica R. Barbery, Omid Saber, Frederick M. Chester, & Judith S. Chester

Published August 15, 2017, SCEC Contribution #7819, 2017 SCEC Annual Meeting Poster #192

As sliding velocities approach seismic slip rates, a significant reduction in the coefficient of friction of rock can occur as a result of weakening of microscopic asperity contacts by flash heating. Utilizing a high-speed, high-acceleration biaxial apparatus equipped with a high-speed Infra-Red (IR) camera, we have documented the spatial distribution of flash temperature on decametric sliding surfaces of rock, which is characterized by linear arrays of mm-size high-temperature spots. Numerical models informed by our observations of surface temperature, and which consider the coupling of changes in temperature and friction of contacts, support the hypothesis that independent mechanisms of flash weakening operate at different contact scales. The uncertainty about the lifetimes and recurrence times of contacts, however, contributes to uncertainty in model results. Here, we report on new rock friction experiments with known lifetimes and recurrence times for millimeter-scale contacts. Experiments conducted in a double-direct shear configuration on Westerly granite samples achieve velocity steps from 1 mm/s to 900 mm/s at high accelerations (~50 g) over short displacements (~2 mm) with normal stresses of 6-8 MPa and 30 mm of displacement during sustained high-speed sliding. Sliding surfaces are machined to produce roughness similar to natural fault surfaces and to preset contact populations. Temperatures observed in thermographs of preliminary experiments on surfaces with contact lifetimes half of the recurrence interval are in good agreement with prediction of 1-D heat conduction models of flash heating. Current work on machined surfaces with different contact population characteristics is being used to test the hypothesis of multi-scale flash weakening.

Key Words
rock friction, flash heating, thermography

Citation
Barbery, M. R., Saber, O., Chester, F. M., & Chester, J. S. (2017, 08). Examination of multi-scale flash-heating at seismic slip rates in granite. Poster Presentation at 2017 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)