Simulating brittle fault evolution from networks of pre-existing joints within crystalline rock

Many faults grow by linkage of smaller structures, and damage zones around faults may arise as a result of this linkage process. In this paper we present the first numerical simulations of the temporal and spatial evolution of fault linkage structures from more than 20 pre-existing joints, the initial positions of which are based on field observation. We show how the constantly evolving geometry and local stress field within this network of joints contribute to the fracture pattern. Markedly different fault-zone trace geometries are predicted when the joints are at different angles to the maximum compressive far-field stress ranging from evolving smooth linear structures to complex ‘stepped’ fault-zone trace geometries. We show that evolution of the complex fault-zone geometry is governed by: (1) the strong local variations in the stress field due to complex interactions between neighbouring joints; and (2) the orientation of the initial joint pattern with respect to the far-field stress.