Shear fractures

A fracture where the relative displacement is parallel to the fracture plane is called shear fracture, or fault if the displacement is significant. Faults may initiate as small-scale shear fractures, or develop during the linking up of small fractures of various types. They normally grow by linking up with gradually larger segments. When faults slip, they normally develop a zone of deformation. Fault zones consist of two main hydrogeological units; the core and the damage zone. The fault displacement is primarily along the core, at the contact between the core and the damage zone.

During slip all the pores and fractures in the damage zone that meet with the fault plane get interconnected, so that the fault suddenly experience a significant increase in permeability (Gudmundsson, 2000b). The permeability of a fault is controlled by the local stress field around and within the fault zone.

 

 

A fault zone of this scale is visible in seismics. This is a carbonate reservoir analogue at Nash Point, Wales UK.