Evolution of frictional strength and fluid flow in shear fractures in granitic rock under hydrothermal conditions

Tamara N. Jeppson, David A. Lockner, Joshua Taron, N. M. Beeler, Stephen H. Hickman, Diane Moore, & Brian D. Kilgore

Submitted August 30, 2026, SCEC Contribution #15221, 2026 SCEC Annual Meeting Poster #TBD

The failure of faults in the brittle crust is dependent on frictional strength and in situ effective stress. Both are influenced by fluid transport properties of the fault zone, yet relatively few studies have examined the evolution of both frictional strength and fluid flow in faults at conditions representative of seismogenic depths. Using simulated faults in granitic rock, we conducted laboratory slide-hold-slide experiments to study the combined evolution of frictional strength and fluid transport properties under hydrothermal conditions up to 250˚C and effective pressures of 20 MPa. We find that the evolution of fault properties is strongly dependent on temperature, time-scale, mineralogy, and fluid chemistry. At room temperature or short hold durations frictional strength increases with the log of hold duration, as has been well described for a variety of materials at room temperature or nominally dry conditions. However, for longer holds and elevated temperatures our experiments show that frictional strength is anticorrelated with the log of hold duration. Weakening is accompanied by increased shear creep during the hold period. Forward modeling of long hold periods at 250˚C using rate and state friction constitutive equations requires a second, strongly negative, state variable that changes with time. While rate and state friction is an empirical model, the first state variable is commonly hypothesized to be related to an increase in contact area as contacts age leading to an increase in friction. The weakening we observed, and the second state variable required to model the behavior, is not consistent with this interpretation. The second state variable may reflect the strain-rate sensitivity of plastic yielding or the reaction rate of a chemical process.

Key Words
Friction, permeability

Citation
Jeppson, T. N., Lockner, D. A., Taron, J., Beeler, N. M., Hickman, S. H., Moore, D., & Kilgore, B. D. (2026, 08). Evolution of frictional strength and fluid flow in shear fractures in granitic rock under hydrothermal conditions. Poster Presentation at 2026 SCEC Annual Meeting.

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