Geologic Structures: Deformation, Faults, and Strike and Dip

A set of vocabulary flashcards covering rock deformation types, stresses, faults, and strike and dip principles from geology lecture notes.

Brittle deformation

Deformation in which a material breaks or cracks to form fractures, typically occurring near the Earth's surface.

Ductile deformation

Deformation in which a material bends or flows within the plastic region, typically occurring at depth.

Elastic deformation

Temporary deformation from which a material rebounds after the deforming stress is removed.

Elastic limit

The point beyond which a rock undergoes irreversible plastic deformation.

Factors determining deformation type

The conditions that dictate whether a rock behaves in a brittle or ductile manner: temperature, confining pressure, rate of deformation, and rock composition.

Compression

A type of stress that causes shortening of the rock material ($\rightarrow \leftarrow$).

Tension

A type of stress that causes stretching of the rock material ($\leftarrow \rightarrow$).

Shear stress

A type of stress that distorts rock ($\downarrow \uparrow$).

Fracture

A planar separation formed in rock.

Joint

A fracture formed due to pressure release without any movement or displacement along the crack.

Fault

A fracture in rock along which displacement has occurred.

Normal fault

A fault formed under tensional stress where the hanging wall slips downward relative to the footwall; most common in regions experiencing crustal tension.

Reverse fault

A fault formed under compressional stress that pushes rock upwards, causing the hanging wall to move upward relative to the footwall.

Thrust fault

A special type of reverse fault characterized by a shallow dip angle of below $35^\circ$.

Strike-slip fault

A fault formed by shear stress with horizontal motion, classified as either right lateral or left lateral.

Strike

The compass direction of a planar rock surface relative to north.

Dip

The angle of inclination measured between a rock surface and a horizontal plane.

Dip direction

The compass direction toward which an inclined plane descends, which is always perpendicular to strike.

Strike and dip map symbol

A geologic map marking where the longer line aligns with the strike direction, the shorter perpendicular tick points toward the dip direction, and the number denotes inclination in degrees.