Earthquakes

1
Earthquakes

• Earths Crust in Motion

2
Stress in the Crust

• Earthquake shaking and trembling that results
  from the movement of rock beneath Earths
  surface.
• Stress a force that acts on rock to change its
  shape or volume (squeeze or pull rock in the
  crust)

3
Types of Stress

• Shearing, tension, and compression work over
  millions of years to change the shape and volume
  of rock.

4
Shearing

• Stress that pushes a mass of rock in two opposite
  directions
• Can cause rock to break and slip apart or to
  change its shape

5
Tension

• Stress force that pulls on the crust, stretching
  rock so that it becomes thinner in the middle
• Occurs where two plates are moving apart

6
Compression

• Stress force that squeezes rock until it folds or
  breaks
• One plate pushing against another can compress
  rock like a giant trash compactor

7
Deformation

• Any change in the volume or shape of Earths
  crust
• Most changes occur slowly
• Caused by the slow shift of the Earths plates

8
Kinds of Faults

• Fault break in Earths crust where slabs of
  crust slip past each other
• Faults usually occur along plate boundaries,
  where the forces of plate motion compress, pull,
  or shear the crust so much that the crust breaks

9
Strike-Slip Faults

• Caused by shearing
• Rocks on either side of the fault slip past each
  other sideways with little up-or-down motion
• Transform boundary
• Example San Andreas fault in California

10
Normal Faults

• Caused by tension forces
• At an angle, so one block of rock lies above the
  fault (hanging wall) and the other lies below the
  fault (footwall)
• Divergent boundary
• Example Rio Grande rift valley in New Mexico

11
Reverse Faults

• Caused by compression forces
• Same structure as normal faults, but blocks move
  in different directions
• Hanging wall slides up over the footwall
• Example Appalachian Mountains, Glacier National
  Park in Montana

12
Friction Along Faults

• How rocks move along the faults depend on how
  much friction there is between the opposite sides
  of the fault.