Stick-Slip Induced Source Ground Vibration in Sheared Granular Fault

Source ground vibration in fault blocks of granular fault with respect to stick-slips is important to understand the dynamic behavior of sheared granular fault system. Here, a two-dimensional implementation of the combined finite-discrete element method (FDEM), which merges the finite element method (FEM) and the discrete element method (DEM), is used to explicitly simulate a sheared granular fault system. In the FDEM model, each plate and each particle is represented by a discrete element, which allows for the tracking of their motion and interactions with neighboring objects, and each discrete element is further discretized into finite elements to capture its deformation to external forces. We focus on investigating the stick-slip induced plate vibrations at places adjacent to the gouge in terms of velocities in directions parallel (x-direction) and perpendicular (y-direction) to the shear direction. The simulation shows that the x- and y-velocities on the upper and lower plates have both positive and negative values. The positive x-velocities with large magnitude are mainly seen on the upper plate and the negative x-velocities with large magnitude mostly occurred on the lower plate; whereas the y-velocities show the opposite characteristics. The x-velocities of both the upper and lower plates are highly concentrated around the half of the shear velocity, while the y-velocities of both plates are stabilized around zero. The average vibrations in the y-direction is about 68% of that in the x-direction, which means the places on plates nearby the gouge vibrate in x- and y-direction in a similar pace, but with different magnitudes. The simulations may help reveal the complexities of earthquake source dynamics.