Stick-slip behavior (DEM)
Dynamic earthquake triggering is the creation of an earthquake by seismic waves, radiated by another earthquake far away from the original fault. Stick-slip in granular materials is known to be the main driving mechanism for failure of fault gouge behavior leading to earthquakes.DEM simulations of a sheared granular layer allow to study the micromechanics of slip triggering. The critical state in granular media is characterized by precursor microslip and frictional weakening. The increase of the precursor rate is a signature for the granular medium being driven towards failure.
Behind avalanche triggering
In granular media, macroscopic phenomena such as avalanches depend on material composition and grain interactions. DEM simulation provides a tool to model grain scale interactions and analyze the macroscopic statistics of avalanche processes.
Before the onset, local reorganizations of grains occur in the granular media. As the critical angle is approached, the frequency of the local organisations intensifies and they concentrate at the depth where the avalanche layer will start sliding. These precursory events can be probed by acoustic emissions in experiments and modeling.
DEM of sound wave transmission
Passive and active acoustic probing of precursor activity allows the analysis of the critical state of granular media. Particles are used as acoustic sensors by recording their dynamic response to external vibrations to determine the evalution of linear and nonlinear elastic properties.
Fluid-solid coupled modeling
Fluids play an important role in the frictional weakening and stick-slip behavior of granular media. In the framework of a collaboration with Los Alamos National Laboratory and Penn State University, dry and wet granular media are analyzed in stick-slip behavior. Fluid-solid coupled modeling using DEM and CFD allows to simulate the frictional behavior of wet granular media. To mimick experiments, we use two corrugated plates to confine the particles and shear the gouge layer. So far, simulations of dry media show frictional weakening of granular materials during critical state, leading to major slips. The friction coefficient and kinetic energy signals confirm presence of precursory microslips.