Seismo Lab Seminar

A fault is a geological discontinuity that accommodates shear displacement (or slip). This is the result of applied loading overcoming frictional resistance. Depending on various conditions, slip may occur rapidly, in the form of an earthquake, or may occur slowly, in the form of aseismic slip transients or steady creep. Here, using a mechanistic approach, we first determine the precise conditions under which a single-asperity finite fault, governed by rate- and-state-dependent friction (following a specific evolution law), is expected to give rise to seismic slip, aseismic slip transients or simply steady creep. We leverage linear and non-linear stability analyses of slip motion to define semi-analytically the critical (minimum) asperity size that could lead to an earthquake or a transient acceleration of creep, as well as to get insights into slip complexity evolution, as a function of governing dimensionless parameters. Full elastodynamic numerical simulations using a newly developed Spectral Boundary Integral Equation Method-based code further support and confirm our theoretical predictions. We then take a step back and examine the consequences of our choice of a particular frictional description. We perform a non-linear stability analysis considering a family of friction laws on a simplified fault model, the so-called spring-block model. Our results indicate that when frictional state deviates from a so-called aging law, even slightly, a characteristic length scale for dynamic slip nucleation does not exist anymore: faults of any size can support an instability provided that a large enough perturbation is applied to slip motion. Our results are consistent with observations of laboratory earthquakes and have important implications for many subsurface engineering technologies, such as geological carbon sequestration or deep geothermal energy extraction.