Towards a more useful description of the structure of brittle fault zones.

Geological faults are not simple planar surfaces in three dimensions. Instead they are zones of variable thickness that can contain several surfaces, each one accommodating a proportion of the total fault displacement. This partitioning of displacement onto several surfaces is significant because it records the evolution of fault zones by processes that include linkage between fault segments. Also, because fault zones often play a key role in controlling fluid flow in the subsurface, displacement partitioning is a key factor in many application areas. Despite it’s importance, displacement partitioning is rarely incorporated into fault zone descriptions and as a result is poorly understood. This presentation will review the internal structure of brittle fault zones and discuss how a geometric model of fault zone evolution based on outcrop and sub-surface mapping can lead to an improved understanding of the distribution of displacement within fault zones. contact: luca.formaggia@polimi.it // marco.verani@polimi.it