Faults and Folds

Normal Fault In normal faulting, the hanging wall block moves down relative to the footwall block. The fault plane usually makes a high angle with the surface (> 45 degrees). Normal faults are associated with crustal tension.

Reverse Fault In reverse faulting, the hanging wall block moves up relative to the footwall block. The fault plane usually makes a low angle with the surface (< 45 degrees). Reverse faults are associated with crustal compression and are also known as thrust faults.

Strike-slip Fault In strike-slip faulting, the two blocks move either to the left or to the right relative to one another.

Joints have many important properties as planes of weakness in rock masses:

Joints and other discontinuities such as faults, cleavage, metamorphic foliation, and bedding planes control many important properties of rock masses including: Strength Compressibility Permeability

GEOLOGIC STRUCTURES Importance of geologic structures –Oil and natural gas are formed and found trapped in subsurface folds –Faults, joints, and fractures can act as a passageway for groundwater and host for valuable mineral deposits as ores of gold, silver and copper, etc. –Unconformities can be used to mark geologic time boundaries