Résumé
We explore processes that govern fault dynamics over the earthquake cycle time-scale using the discrete element method (DEM). Here, we especially investigate the effects of fault geometries on the mode of fault slip, focusing on the configurations that lead to slow-slip events and earthquakes. The model used here consists of a 2D cohesive assemblage of about 12,000 particles, bonded at all contacts except along a pre-defined centered fault surface of 50 km length. A constant velocity is imposed at the walls of the fault blocks to induce general strike-slip fault tectonic loading. This particle-based model reproduces a wide variety of slip-modes, from stable-slip to slow-slip, as well as fast earthquakes, with characteristics similar to natural cases. Indeed, coseismic slip gradients, slip-velocities and accelerations are, to first order, consistent with typical values inferred from geodetic and seismological data. In this study, we define fault surface morphologies by combining periodic functions at different scales (i.e., Fourier series), with the specific goal of developing distinctive along-strike stress distributions to examine their effects on the fault slip dynamics. Consistent with recent studies using DEM models of subduction megathrusts, we find that many nucleation regions exhibit precursory stress-changes related to the gradual unlocking of geometrical asperities (i.e., protrusions) before the onset of dynamic slip. This precursory stage is illustrated by the occurrence of slow-slip events that evolve into earthquake instabilities. We investigate this process in detail, to understand the conditions that allow these slow-slip events to turn into earthquakes, in contrast to those that cause slow slip events to simply stop. The advantages of using the DEM approach is to provide such comparisons by stress-strain analyses at all spatial and temporal scales, from the asperity scale to the full length of the fault, and from the earthquake nucleation stage to the time-scale of several seismic cycles.