Earthquakes I: Stress and Strain

Earthquakes May Result From…

• rupture of a fault
• movement of magma
• landslides
• any other rapid release of energy that shakes the ground
• stresses

Stresses

1. compressional stress

   
   1. forces opposite
   2. acts toward each other

2. tensional stress

   
   1. forces opposite
   2. act away from each other

3. shear stress

   
   1. forces opposite
   2. act parallel but across a plane

Strain

• strain: when a solid material is put under stress, it will respond by deforming (change in shape or size)
• what type of change occurs depends:
    * temperature and pressure
    * properties of the material being subjected to stress
    * speed of deformation
    * duration of deformation
• 3 different types of deformation:

  
  1. elastic deformation: temperature change in shape or size

     
     1. recovers when stress is removed
  2. plastic (ductile) deformation: permanent change in shape or size

     
     1. not recovered when stress is removed
     2. ex: fold in limestone
  3. brittle deformation: loss of cohesion due to stress

     
     1. sub-planar surfaces separating coherent zones
     2. ex: fault