Quantifying the Effects of the Value of Absolute Friction and Geometrical Symmetry on Dip-Slip Faults

Abstract

Many earthquake models assume a symmetric fault for which the normal stress does not change over the course of the earthquake process, the results of which are insensitive to the absolute values of the frictional coefficients. However, a break in geometrical symmetry will generally lead to a more complex rupture process where the absolute friction value influences the results. In this study, we explore the influence of static and dynamic friction on the spatiotemporal evolution of rupture and slip along shallow dip-slip faults, where geometrical symmetry is broken by the addition of the free surface at an acute angle to the fault. We utilize a 2D finite-element method to model the dynamics of thrust and normal faults. Our results show that dynamic friction, via its multiplicative relationship to the time-dependent normal stress, has a noticeable effect on the time evolution of shear stress, stress drop, and fault slip in shallow dip-slip faulting scenarios. In our parameterizations, the magnitude of the effect on slip at the Earth’s surface is between roughly 8% and 20%. The effect appears under a variety of different modeling assumptions, including homogeneous and heterogeneous initial stress, and different levels of average stress. This effect is inversely related to fault burial depth and disappears entirely for deeply buried (purely symmetric) faults. The effects of the absolute friction value that are identified in our study may be hidden in existing dynamic rupture models that utilize an assortment of different values for frictional coefficients. Therefore, future researchers should be aware of their physical impacts when interpreting existing work and when choosing frictional values.