Velocity-weakening behavior of granite and gabbro at temperature up to 600 degrees C (INVITED)

Abstract eng:
The depth extend of seismicity in the Earth’s crust is believed to be controlled by a temperature-dependent transition from velocity-weakening to velocity-strengthening friction. Available experimental data on granite suggest a transition from unstable slip to steady creep at temperature about 350 ◦ C. We present results of unconfined experiments on granite and gabbro at both dry and hydrated conditions that show increasingly unstable slip (velocity-weakening behavior) at temperatures up to 600 ◦ C. We estimate the rate-state friction parameters using velocity-stepping tests and by fitting the data to predictions of a 1-D spring-slider model. We find that the “evolution” parameter b increases with temperature at a higher rate than the “direct effect” parameter a. We also find that the aging law provides a better fit to our experimental data compared to the slip law. Obtained results may help explain anomalously deep crustal seismicity in regions of active extension and convergence.

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