Fault models

Boundaries between plates are made up from a system of faults. Each type of boundary is associated with one of three basic types of fault, called normal, reverse and strike-slip faults.

You can use pieces of foam or card to model the movement of tectonic plates in different kinds of faults and boundaries. The images below show simple foam models of faults: those on the left show ‘before slippage’ and those on the right ‘after slippage’.

Normal faults

Normal faults are associated with divergent plate boundaries: for example, the Mid Atlantic Ridge that is exposed above sea level through Iceland.

Normal fault, before slip
Normal fault, after slip

Reverse faults

Reverse faults (or 'thrust' faults) are found at convergent boundaries. They are associated with mountain ranges, such as the Himalayas or the Andes.

Reverse fault, before slip
Reverse fault, after slip

Strike-slip faults

Strike-slip faults occur at transform boundaries: for example, a system of strike-slip faults makes up the transform boundary of the San Andreas fault.

Strike-slip fault, before slip
Strike-slip fault, after slip

Examples of strike-slip faults

Small offset from a single  earthquake in California (M 6.9 strike-slip event in 1979).
 Aerial view of streams along the San Andreas fault.