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.
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