oa 3D Discrete Element Method Modelling of Fault Zone Internal Structure

Faults are often simplified as planar structures but are, in reality, complex zones comprised of multiple slip surfaces that contain variably deformed rock volumes, ranging from intact fault bound lenses to fault rock (breccia, gouge). This sub-resolution structure has a direct impact on the juxtaposition geometries across faults and ultimately their impact on fluid flow. We use a commercially available implementation of the Discrete Element Method (DEM), which represents rock as an assembly of cemented spheres, to model the propagation of normal faults through mechanically layered sequences. The fault zone evolution observed in the models demonstrates the main processes thought to be the cause of internal complexity in fault zone structure and the model faults replicate a range of features observed in normal faults at outcrop; these include multi-stranded fault zones, relay zones, normal drag, asperities and corrugated fault surfaces. Systematic variation in the internal structure of model faults with both changes in the lithological sequence and confining pressure suggest that this type of modelling can provide a basis for evaluating the likely complexity of fault zone structure and associated sequence juxtapositions.