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A series of discrete elements simulations is presented for the study of fault gouges' frictional response. The gouge is considered to have previously undergone ultra‐cataclastic flow and long‐time consolidation loading. We explore the effect of different particle characteristics such as size, polydispersity, and also shearing velocities on gouge's response under the conditions met in the seismogenic zone. Monte‐Carlo analyses suggest that the local stick‐slip events disappear when averaging over a large number of numerical samples. Moreover, the apparent material frictional response remains almost unaffected by the spatial randomness of particles' position and by the particle's size distribution. On the contrary, the mean particle size controls the formation and thickness of the observed shear bands, which appear after the peak friction is met. Furthermore, the apparent friction evolution fits well to an exponential decay law with slip, which involves a particle size dependent critical slip distance. For the studied conditions and depth, the shearing velocity is found to play a secondary role on the apparent frictional response of the gouge, which highlights the importance of analyses involving multiphysics for studying the rheology of fault gouges. Besides improving the understanding of the underlying physics of the problem, the above findings are also useful for deriving pertinent constitutive models in the case of modeling with continuum theories. Plain Language Summary: Understanding the response of a fault gouge, the granular material at the core of fault zones, can shed light on the way earthquakes are nucleated. For this purpose, in this paper, a series of particle‐based simulations of a fault gouge, under conditions similar to the ones expected at deep down at the seismogenic zone, are conducted. A full‐scale fault with dimensions of the order of kilometers is almost impossible to be simulated at the grain‐scale. In order to capture the inhomogeneities at this level, the response of several, small samples is combined in a stochastic‐ensemble manner. The results suggest that local stick‐slip events are vanishing with increasing number of tests thus, they are not critical for the macroscopic, global, material's response. Contrary to this, the amount of slip needed to promote earthquake instabilities is shown to vary with respect to the mean particle size of the material. Finally, the granular polydispersity and the slip velocity do not seem to affect the system's behavior. The later highlights possible important role of multiphysics on the rheology of fault gouges and provides evidence for the constitutive assumptions used in continuum models. Key Points: The local stick‐slip motion vanishes for multiple, averaged tests and does not affect the expected value of the apparent frictional responseBoth the thickness of the principal slip zone and the critical slip distance scale with the mean particle diameterParticle size distribution and shearing velocity exerts a second order control on global friction [ABSTRACT FROM AUTHOR]

Earthquakes nucleate when large amounts of elastic energy, stored in the earth's crust, are suddenly released due to abrupt sliding over a fault. Fluid injections can reactivate existing seismogenic faults and induce/trigger earthquakes by increasing fluid pressure. Here we develop an analogous experimental system of simultaneously loaded and wetted absorbent porous paper to quantify theoretically the process of wetting‐induced earthquakes. This strategy allows us to gradually release the stored energy by provoking low intensity tremors. We identify the key parameters that control the outcome of the applied injection strategy, which include the initial stress state, fault segmentation, and segment‐activation rate. Subsequent injections, initiated at high stress levels, can drive the system faster toward its instability point, nucleating a large earthquake. Starting at low stress levels, however, they can reduce the magnitude of the natural event by at least one unit. Plain Language Summary: Understanding natural and anthropogenic seismicity is a major scientific challenge. Here we present a novel analogue fault model using absorbent porous paper, which gives new insights on earthquake mitigation. When scaled to in‐situ conditions, the porous paper model represents a natural seismic rupture of magnitude Mw = 5.9. By progressively wetting it, we simulate fluid injections in the earth's crust and draw analogies to large‐scale industrial projects. In our experiments, each injection is accompanied by tremors, which progressively release energy and modify the energy budget of the system. Without precise knowledge of the fault properties, we risk driving the system faster toward an unexpected large seismic event. However, provided that the model's key parameters–fault segmentation, segment‐activation rate, and stress state–are well known or controlled, the natural rupture can be mitigated by at least one unit. We expect that these results will facilitate risk reduction in current fluid injection projects and inspire earthquake mitigation strategies for real tectonic faults. Key Points: From an energetic point of view, absorbent porous paper can be an ideal, low‐cost surrogate rock material for studying induced seismicitySegmentation of faults and sequential fluid injection in each segment can mitigate potential earthquakes by at least one order of magnitudeWe show that fault segmentation, segment‐activation rate and stress state predominantly control the result of applied injection strategies [ABSTRACT FROM AUTHOR]