Motion picture

Terje Solbakk (Text and photo)


Photo: Terje Solbakk

Faulting is a normal term in structural geology, and means that rock has been subject to such substantial mechanical loads that it rips apart. Movement along this fracture zone is what creates a fault – if no shift occurs, it remains a crack.

The angle of faulting can vary from vertical to almost horizontal. Moreover, special names have been given to the rock on either side of a fault. The part on top is called the hanging wall and that below is the footwall.

A normal fault is one where the hanging wall has been thrust down in relation to the footwall (as in the photograph above). If it has been thrust up, the term is a reverse fault. And displacement to one side is a strike-slip fault.

The movement in itself may be small, and the term “fault displacement” is used to describe the amount involved. It could be anything from a few millimetres to kilometres.

A fault seldom occurs alone, and the movement between hanging wall and footwall could be distributed between several faults which occur together in a fault zone.

Fault displacement can occur very quickly, and several times over geological time – with each movement often separated by many millions of years.

Mapping and understanding faulting is crucial for petroleum production on the NCS. Several of its oil and gas fields are found in structures created by faults.

Faulting within reservoirs can influence productivity, either by being open so that oil and gas pass through or because finegrained rocks create a seal and prevent flow.

Topics: Geology