Anextensional fault is afault caused by stretching of theEarth's crust.[1] Stretching reduces the thickness and horizontally extends portions of the crust and/orlithosphere.[2] In most cases such a fault is also anormal fault, but may create a shallowerdip usually associated with athrust fault. Extensional faults are generallyplanar. If thestress field is oriented with the maximum stress perpendicular to the Earth's surface, extensional faults will create an initial dip of the associatedbeds of about 60° from the horizontal. The faults will typically extend down to the base of theseismogenic layer. As crustal stretching continues, the faults will rotate, resulting in steeply-dipping fault blocks between them.
