L4 | STRESS AND STRAIN

• STRESS

  • force applied to an object.
  • force per unit area that is placed on a rock. 
• 4 TYPES OF STRESSES:

  1. CONFINING
  2. TENSION
  3. COMPRESSION
  4. SHEAR
• CONFINING

  • deeply buried rock is pushed down by the weight of all the material above it
• TENSION

  • Rocks are pulled apart
  • Force acting perpendicular to and away fro a surface
  • Major type of stress at divergent plate
• COMPRESSION

  • Pushed together
• SHEAR

  • Parallel but in opposite direction
  • Force acting parallel to a surface
  • Most common stress at transform plate boundary
• STRAIN

  • Deformation
  • Change in solid’s shape caused by the application of stress
• 2 KINDS OF DEFORMATION

  1. ELASTIC DEFORMATION
  2. PLASTIC DEFORMATION
• ELASTIC DEFORMATION

  • the rock returns to its original shape when the stress is removed.
• PLASTIC DEFORMATION

  • rock does not return to its original shape when the stress is removed.
• FRACTURE

  • Happens when rock breaks
• FOLDS

  • Bend in the rock in response to compressional forces
  • Noticeable in rocks with stratification
• 3 TYPES OF FOLD:

  1. MONOCLINE
  2. ANTICLINE
  3. SYNCLINE
• MONOCLINE

  • Bend in the rock layer so that they are no longer horizontal
• ANTICLINE

  • Folding of rock into arch-like shape
  • Oldest beds
• SYNCLINE

  • Fold that bends downward
• 3 TYPES OF FOLD

  A) MONOCLINE

  B) ANTICLINE

  C) SYNCLINE

  
• FAULT

  • Fracture or zone of fractures between 2 blocks of rock
  • Allows the block to move relative to each other
• 3 TYPES OF FAULT:

  1. NORMAL FAULTING
  2. REVERSE FAULTING
  3. STRIKE - SLIP FAULTING
• NORMAL FAULTING

  • Crust is being pulled apart in which the overlying block moves down with respect to the lower block.
• REVERSE FAULTING

  • Crust is being compressed in which the hanging wall block moves up and over the footwall block
• STRIKE-SLIP FAULT

  • Dip-slip fault in which the dip of the plane is vertical 
  • Result from shear stress
• 3 MAIN TYPES OF FAULT:

  A) NORMAL FAULT

  B) REVERSE FAULT

  C) STRIKE-SLIP FAULT

  
• 3 STAGES OF DEFORMATION:

  1. FRACTURE DEFORMATION
  2. ELASTIC DEFORMATION
  3. DUCTILE DEFORMATION
• FRACTURE DEFORMATION

  • irreversible strain, rock breaks because it is brittle
• DUCTILE DEFORMATION

  • strain is irreversible
  • changes in its shape are permanent, and the material is no longer able to revert to its original shape
• SLIP

  • distance that rocks move sideways a fault
  • can be up or down the fault plane
• DIP SLIP FAULT

  • fault's dip is inclined relative to the horizontal surface
• OBLIQUE SLIP FAULT

  • fault which has components of dip slip and strike slip
• TYPES OF STRESS

  A) CONFINING

  B) TENSION

  C) COMPRESSION

  D) SHEAR