Temperature Dependent Frictional Properties of Crustal Rocks
In this dissertation, I study the effects of temperature on frictional properties of crustal rocks at conditions relevant to earthquake nucleation. I explore how temperature affects fault healing after an earthquake. I present results from slide-hold-slide experiments on Westerly granite that show that frictional healing rate increases slightly and shear strength increases with temperature. Based on our results, if the effects of temperature are neglected, fault strength could be under-predicted by as much as 10 percent. I use finite element numerical experiments to show that our frictional healing data can be explained by increases in contact area between viscoelastic rough surfaces. I investigate the influence of temperature on the transition from seismogenic slip to aseismic creep with depth in continental crust. I present results from velocity-stepping and constant load-point velocity experiments on Westerly granite conducted at a wide range of temperatures. I construct a numerical model incorporating the rate-state friction equations to estimate the values of (a-b) that provide the best fit to the stick-slip data. I find that sliding becomes more unstable ((a-b) < 0) with temperature up to the maximum temperature tested, 600 ºC. This contradicts a traditional view that the deep limit to seismicity in continental upper crust is caused by a transition to stable creep ((a-b) > 0) in granite at temperatures above ~350 ºC. These results may help explain the occurrence of anomalously deep earthquakes found in areas of active extension and convergence. I explore the frictional properties of gabbro at conditions corresponding to slow slip events in subduction zones. I present results from experiments on gabbro conducted at low effective normal stress and temperatures between 20-600 ºC. I find that (a-b) decreases with temperature based on direct measurements and numerical modeling. I conclude that the occurrence of slow slip events at the base of the seismogenic zone cannot be fully explained by a transition to nearly velocity-neutral friction in gabbro at temperature of ~350 ºC. Conditions of high water fugacity or the presence of clay minerals may play an important role in the occurrence of slow slip events in subduction zones.