What is a fault?

Part of Hall of Planet Earth.

What is a Fault? AMNH/R.Mickens

A fault is a rock fracture along which movement occurs. Normal faults develop where the crust stretches apart, as in the East African Rift Valley. In thrust faults, which are found at subduction zones, the rocks on one side of the fault are pushed up and over those on the other side. A third type of fault is the strike-slip fault, where the rocks on either side of the fault slip by each other horizontally. The San Andreas Fault is a strike-slip fault.

Types of Faults_ILL

In This Section

Exhibit Fault in Crystalline rock This near-vertical fault in granitic gneiss offsets a black basaltic dike. Exhibit Which way does a fault move? Slickensides are grooves and steps created on a fault surface by the slow, grinding movement of two bodies of rock against each other.