Lecture 12// Crustal Deformation, Faults Flashcards
Stress
A force applied:
• tension
• compression
• shear
Strain
Deformation that results from stress: • fractures, joints • regional tilt • faults • folds • crustal thinning
Brittle deformation
Stress applied relatively quickly and/or near the surface results in fractures/joints, and faults.
Ductile deformation
Stress at depth and over long periods of time results in folding (via compression) or crustal thinning (via tension).
Fault
Brittle deformation involving sudden displacement along a fault plane.
Fault plane
The surface of rupture.
Footwall block
The block that sits below the fault plane.
Hanging wall block
The block that sits above the fault plane.
Strike
The intersection between a dipping bed/ planar feature, and a horizontal surface.
Dip
The direction and angle of incline of a bed or planar feature (such as a fracture or fault).
Normal Faults
If the hanging wall goes down with respect to the footwall then it is called a normal fault.
Normal faults are caused by tension.
Reverse / Thrust fault
If the hanging wall goes up with respect to the footwall then it is either a reverse fault or a thrust fault. These faults are caused by compression.
• Thrust fault if dip angle is
less than 20°.
dip-slip faults
Types of Normal & reverse/thrust faults.
• Displacement has occurred in a vertical sense along the dip of the fault plane.
Strike-Slip Faults
- left-lateral
- right-lateral
If neither the hanging wall nor the footwall moves relative to each other, and instead the motion is lateral, then it is called a strike-slip fault. These are caused by
shear stress.
Orogenesis
The building of mountain belts. • Three types of mountain belts: 1. Volcanic Mountains 2. Fault-Block Mountains 3. Fold-and-Thrust Mountains
