Strike and dip

Strike is the compass direction of a horizontal line on a planar geological feature; dip is the feature’s angle and direction of inclination from horizontal.

Dip direction: The compass direction toward which a geological plane slopes downward most steeply. Together with dip angle, it specifies the direction of inclination.
Geologic cross-section: A vertical slice through geological units showing their structure beneath the ground surface. Strike and dip measurements constrain the geometry drawn between map observations.
Plane (geometry): A flat, two-dimensional surface extending without bound in three-dimensional space. Strike and dip describe the orientation of a geological plane.
Lineation (geology): A linear fabric or feature in rock defined by aligned minerals, elongate grains, or structural elements. Strike and dip describe planes, whereas lineation records a line’s orientation.
Apparent dip: The inclination of a plane measured in a vertical section that is not perpendicular to its strike. It differs from true dip, which is measured perpendicular to strike.
Fold (geology): A bend in originally planar rock layers produced by deformation. Changing strike and dip across an area reveal folded strata.
Azimuth: A horizontal angle measured clockwise from a reference direction, usually north. Strike is commonly recorded as an azimuth.
Trend and plunge: The compass direction and downward angle of a line in three-dimensional space. These describe linear features rather than planar surfaces.
Right-hand rule: A convention that assigns a plane’s dip direction as 90 degrees clockwise from its strike azimuth. It removes ambiguity when recording strike and dip.
Fault (geology): A fracture or zone of fractures along which rocks have moved relative to one another. Fault-plane orientation is described by its strike and dip.

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