Extensional fault

Array of extensional faults cutting Triassic to Lower Jurassic Blomidon Formation rocks, near Clarke Head, Minas Basin North Shore, Nova Scotia, position of faults highlighted in black, marker bed highlighted in green

Students examine an extensional fault, up close

An extensional fault is a fault that vertically thins and horizontally extends portions of the Earth's crust and/or lithosphere. In most cases such a fault is also a normal fault, but may be rotated to have a shallower geometry normally associated with a thrust fault. Extensional faults are generally planar and, so long as the stress field is orthogonal to the Earth's surface initiate with a dip of 60° typically continuing down to the base of the seismogenic layer.