Brittle fracturing in low-porosity rock and implications to fault nucleation

We present a two-dimensional conceptual model to investigate the mechanisms of brittle fracturing in low-porosity rock. Biaxial compression tests are simulated on rock specimens containing preexisting fractures, in which the local fracturing processes leading to fault nucleation are closely observed. The impact of fracture configuration and applied confining pressure on brittle fracturing behavior is particularly studied. The simulation results show that (1) reduction of the coordination number in a local region is an accurate indicator of the location, time and degree of local fracturing; (2) each preexisting fracture configuration develops its own local stress field significantly different from one another, which accounts for the differences in fracturing phenomena; (3) gradual modification of the local stress field promotes progressive fracturing, while stress release leads to significant local fracturing or no fracture by means of particulate flow. With the decreased overlap of preexisting fractures, a gradual transition from a band of damage zone linking the preexisting fractures to isolated damage zones enclosing the first-generation fractures is observed in the simulated scenarios. Based on field observations of damage zones and local stress field, two possible mechanisms of fault nucleation are illustrated. This study establishes a potential bridge between geological investigations of fault structures and the theoretical context of microfracture growth.