Fault plane

A fault plane is an idealized planar surface across which rock has slipped. A curved fault can be described by local fault planes. Its orientation is specified by fault strike and fault dip, and the slip direction within it by fault rake.

The fault rake specifies the slip direction within a fault plane. With an along-strike unit vector $\mathbf{s}$ and a down-dip unit vector $\mathbf{d}$, one explicit convention is $\mathbf{b}/b=\cos \lambda \mathbf{s}-\sin \lambda \mathbf{d}$. Positive $90^{\circ }$ then denotes up-dip slip. A convention must accompany a signed fault rake.

The fault dip is the angle between a fault plane and a horizontal plane, measured perpendicular to fault strike towards the descending side. It lies between $0$ and $90^{\circ }$.

The fault strike is the azimuth of the intersection of a fault plane with a horizontal plane. A right-hand convention chooses the along-strike direction for which the fault dips to the observer's right.