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Earthquakes typically exhibit recurrence times that far exceed time-scales attainable in a laboratory setting. To traverse the temporal gap between the laboratory and nature, the slide-hold-slide test is commonly employed as a laboratory analogue for the seismic cycle, from which the time-dependence of fault strength may be assessed. In many studies it is implicitly assumed that all fault restrengthening emanates from an increase in the internal friction coefficient, neglecting contributions from cohesion. By doing so, important information is lost that is relevant for numerical simulations of seismicity on natural faults, as well as for induced seismicity. We conduct slide-hold-slide experiments on granular halite gouge at various normal stresses to assess the time-dependence of the internal coefficient of friction, and of the cohesion, independently of one another. These experiments reveal that both the internal friction coefficient and cohesion increase over time, but that these quantities do not share a common evolution, suggesting different underlying mechanisms.

International audience; Intergranular pressure solution is a well‐known rock deformation mechanism in wet regions of the upper crust and has been widely studied, especially in the framework of compaction of granular materials, such as reservoir sandstones and fault rocks. Several analytical models exist that describe compaction creep by stress‐induced mass transport, and the parameters involved are relatively well constrained by laboratory experiments. While these models are capable of predicting compaction behavior observed at relatively high porosities, they often overestimate compaction rates at porosities below 20% by up to several orders of magnitude. This suggests that the microphysical processes operating at low porosities are different and are not captured well by existing models. The implication is that available models cannot be extrapolated to describe compaction of sediments and fault rocks to the low porosities often reached under natural conditions. To address this problem, we propose a new, thermodynamic model that describes the decline of pressure solution rates within individual grain contacts as a result of time‐averaged growth of asperities or islands and associated constriction of the grain boundary diffusion path (here termed grain boundary evolution). The resulting constitutive equations for single grain‐grain contacts are then combined and solved semianalytically. The compaction rates predicted by the model are compared with those measured in high‐strain compaction experiments on wet granular halite. A significant reduction in compaction rate is predicted when grain boundary evolution is considered, which compares favorably with the experimental compaction data.