There are 3 types of faults based upon relative movement of the hanging wall - normal, reverse and strike-slip. Anderson (1951) predicts a 60 degree dip for normal faults, 30 degree for reverse faults and 90 degree dip for strike-slip faults (Fig. 1). Its worth reading Fossen (2016) to get more background on this.

When studying faults in outcrops it is common to see conjugate sets of faults - a pair of common origin but dipping in the opposite direction. The normal faults in Fig. 1 form a series of conjugate sets - a faulted pair, both dipping at 60 degrees (and separated by a 60 degree angle) but in opposite directions. This too is predicted by Anderson and should be an integral part of any seismic interpretation.

The vertical fault in the cored mudstone in Fig. 2 can be rotated such that it has a 60 degree dip by simply flattening the bedding (picked out by blue lines) i.e., rotating the core - as we’d expect the beds to be horizontal when deposited.

It’s really important to bring Anderson’s model to the fore of any seismic interpretation. For example if a normal fault does not have a 60 degree dip then it must have been rotated or there is a mechanical explanation (plane of weakness). The latter is because the Anderson model does not predict low angle faults - which may initiate due to a pre-existing anisotropy such as a weak salt layer.

Figure 1. Conjugate faults - note the contrast between iron stained deformation bands and the pristine host rock in the foreground. The outcrop is the Permo-Triassic Hopeman Sandstone, Inner Moray Firth, UK.

Figure 2. Flattening of these shales beds (Picked out by blue lines; North Sea core) brings the normal fault to c. 60 deg dip.

Reference

Anderson, E.M. 1951. The Dynamics of Faulting. Edinburgh: Oliver & Boyd.

Fossen. H. 2016. Structural Geology. 2nd Ed. Cambridge University Press.