Summary Deformation

Deformation
Deformation of Rock: Stress-Strain Recap
Stress – forces applied to a rock by Earth movements or the mass of overlying rock

Strain – a change in the shape or volume of a body as a result of applied stress

Factors that Affect a Rocks Behaviour

• Temperature – higher temperature makes the rock more plastic
• Time – slow = fold, fast = fracture
• Pressure – confining pressure – depth into crust
• Strength – composition determines whether it is competent or incompetent


Faults
Principal Stress Orientations Heave
Throw
Maximum Stress Pmax σ1
Intermediate Stress Pmin σ2
Minimum Stress Pint σ3


Normal Fault (Tensional Stress)


Pmax

Footwall Hanging Wall

Pmin →  Pmin Thrust Fault (Compressional Stress)

Pmin
  
Pint Pmax

 Pmax
Reverse Fault (Compressional Stress)
Pmax →

Pmin  
 Pint Pmin


Pmax →  Pmax Strike Slip Fault (Shear Stress)

Pmax Pmin
  

Pint
Pmin


SWAN – Synclines are Wider on the downthrown side
and Anticlines are Narrower 
Pmin 
 Pmax
Pint