Experimental evidence for different strain regimes of crack populations ina clay model

We report results from clay extension experiments used as a model for the e volution of fault populations due to stress interactions. At yielding crack s begin to appear and the brittle strain due to them quickly reaches a rate matching the applied stretching rate. The crack density (number of cracks per unit area) initially increases apace, then reaches a maximum at a criti cal strain, decreasing thereafter. At low strains, where the crack populati on is dilute, a power law length distribution is observed, which at high st rain, gradually transitions to an exponential. This agrees with fault popul ations data observed in low and high strain settings. These results indicat e that fault populations ranging from power law to exponential size-frequen cy distributions reflect the population evolution with increased strain.