Anisotropy, pore fluid pressure and low angle normal faults

Low angle normal faults (LANFs) are commonly associated with high-angle normal faults, high pore fluid pressures and foliated fault cores. Explanations for LANF slip based on high pore fluid pressure critically depend on stress rotations in the fault core zone, which have been based on an assumption of isotropy. Anisotropy fundamentally changes the coupling between pore fluid pressure and effective stress. The response of saturated fault core rocks in LANFs can be explored by combining the Effective Medium Theory with anisotropic poroelasticity. The nucleation and evolution of LANFs are investigated in a framework of local changes in rock properties and the interaction of a pressurised pore fluid with intrinsic (lithological) and extrinsic (damage) anisotropies. This quantitative approach enables comparison with detailed field and laboratory measurements of fault rock properties.