The effects of temperature and pressure on thermal pressurization in localized fault zones

Nir Z. Badt, Terry E. Tullis, Greg Hirth, & Christian Huber

Submitted August 16, 2021, SCEC Contribution #11505, 2021 SCEC Annual Meeting Poster #153

Thermal pressurization (TP) of pore fluids is predicted to be a dominant frictional weakening mechanism during earthquakes. The current prevailing models for frictional sliding with TP assume constant hydraulic and thermal properties (e.g., permeability) of the fault rocks (the constant case). However, temperature and pore pressure in the fault zone inherently change during TP, causing the fault zone rock’s physical, thermal and hydraulic properties to change as well. We present a model for a localized fault zone, where slip is restricted to a plane, with temperature- and effective stress-dependent thermal and hydraulic properties (the variable case). We examine three different lithologies; Frederick diabase, Westerly granite and Hanaore fault gouge, from Japan. The former two crystalline rocks have a very low permeability and (<10-19 m2) and porosity (<1%), the gouge is more permeable (~10-17 m2) and more porous (~17%). Our results show that the low permeability crystalline rocks exhibit more frictional weakening and less temperature rise in the variable case, compared to the constant case. For the fault gouge, however, the variable case exhibits less frictional weakening, resulting in greater temperature rise in the fault zone, compared to the constant case. Furthermore, our model predicts continuous evolution of the two main parameters that control fluid pressurization, the pressurization factor and hydraulic diffusivity. Both increase initially with pore pressure and temperature, though once the temperature in the fault zone exceeds ~250 ℃ pressurization factor decreases, while hydraulic diffusivity decreases at temperatures >300 ℃. Our analysis underlines the importance of considering variable temperature- and pressure-dependent fault zone properties when modeling thermal pressurization.

Key Words
Thermal pressurization, dynamic weakening, friction

Citation
Badt, N. Z., Tullis, T. E., Hirth, G., & Huber, C. (2021, 08). The effects of temperature and pressure on thermal pressurization in localized fault zones. Poster Presentation at 2021 SCEC Annual Meeting.


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