Thermal pressurization evolution with total slip

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

Published August 15, 2018, SCEC Contribution #8757, 2018 SCEC Annual Meeting Poster #181

Dynamic weakening by thermal pressurization is studied on nominally flat surfaces of Frederick Diabase with a rotary-shear apparatus. Experiments are performed at a normal stress of 50 MPa, confining pressure of 45 MPa and pore fluid pressure of 25 MPa. Two types of surfaces are tested: (1) surfaces that underwent little initial displacement (<20 mm, low displacement - LD) and (2) surfaces that underwent large initial displacement (>1 m, high displacement - HD). While both types of surfaces display dynamic weakening at a slip rate of 2.5 mm/s (differing from their dry behavior – velocity strengthening), their frictional behavior differs significantly. LD surfaces exhibit dramatic weakening at the initial stages of fast-slip (40% drop in shear stress over the first ~3 mm of slip), followed by a healing stage, whereas HD surfaces weaken moderately over longer distances (34% drop in shear stress over ~60 mm of slip). The experimental data is compared to a thermal pressurization model (Rice, 2006), where the LD surfaces fit the model for only the initial stages of fast slip and exhibit decay distance of L*=12 mm, and HD surfaces better fit the model with L*=327 mm. Differences that arise between the data and the model lead us to explore a numerical solution to the thermal pressurization problem using spatially and temporarily variable hydraulic parameters, e.g. permeability, to supplement and compare to the model by Rice (2006) which solves for constant hydraulic parameters. Because the hydraulic properties depend on the effective stress which varies in space and time, this type of solution may be more realistic than that of Rice (2006).

Key Words
Thermal pressurization, Experimental, Dynamic weakening

Citation
Badt, N. Z., Tullis, T. E., & Hirth, G. (2018, 08). Thermal pressurization evolution with total slip. Poster Presentation at 2018 SCEC Annual Meeting.

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