Quantifying the Effects of Absolute Friction on Thrust Fault Rupture

Adam Margolis, David D. Oglesby, Baoning Wu, Christodoulos Kyriakopoulos, & Kenny J. Ryan

Published September 10, 2023, SCEC Contribution #12921, 2023 SCEC Annual Meeting Poster #137 (PDF)

Absolute friction has been theorized to have a measurable influence on thrust fault rupture, though its effects have not been completely documented. During slip, an asymmetric fault experiences changes in normal stress, which feed back into the shear stress via the absolute value of the frictional coefficients. In this study, we use 2D dynamic rupture models to quantify the contributions of absolute friction and degree of geometrical symmetry on the temporal evolution of thrust fault rupture and slip.

We compare models with the same stress drop and strength excess while varying our absolute friction in three different ways: (a) increasing both static and dynamic friction such that their difference remains constant, (b) holding dynamic friction at 0.1 while varying the static friction, and (c) holding static friction at 0.6 while varying the dynamic friction.

For each friction configuration, three models are conducted: (1) a strongly asymmetric case where the upper fault tip terminates at the free surface; (2) a moderately asymmetric case where the upper fault tip is buried 9 km (a blind thrust in a half-space); and (3) an essentially symmetric case where the upper fault tip is buried 120 km (a fault effectively in a whole-space).

Preliminary results for a purely symmetric fault in a whole-space (case 3) demonstrate that different frictional and stress parameterizations produce identical displacements. Thus, only the drop in friction contributes to slip for our model in this case. For the models that approach the free surface, where free-surface-induced normal stress variation is apparent, we find that the evolution of fault rupture and slip does depend on the absolute level of friction. Increasing the frictional coefficients leads to an increase in normal stress feedback and slip, where the effect is dominated by the dynamic friction.

Our findings demonstrate how friction and geometry together affect the temporal evolution of slip and stress on asymmetric faults.

Key Words
Thrust, Fault, Modeling, Earthquake, Rupture, Stress, Slip, Displacement, Fault Mod, Simulation, Friction, Symmetry, Asymmetry

Citation
Margolis, A., Oglesby, D. D., Wu, B., Kyriakopoulos, C., & Ryan, K. J. (2023, 09). Quantifying the Effects of Absolute Friction on Thrust Fault Rupture. Poster Presentation at 2023 SCEC Annual Meeting.

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