What Causes this

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					What Causes this?

     Faults
San Francisco 1906
San Francisco 1989
Chile
Before and after
             What is at fault?
• We’ve talked about the movement of tectonic
  plates.
• We have also mentioned the different types of
  boundaries:
              Convergent
              Divergent
              Transform
•Can anyone tell me what happens between the plates
at each of these boundaries?
• When these tectonics plates move, the rocks
  adjacent to these boundaries changes shape.
  – Deformation: is the bending, tilting and breaking
    of the Earth’s crust; the change in the shape of
    rock in response to stress.

  – Rock layers bend under stress, but enough stress
    can cause these layers to reach their elastic limit
    and break
• Folding: is the bending of rock layers due to
  stress.
Ever notice how some materials bend
 under pressure while others break?
                 There are two types of stress
                           that are
                   involved in the collision
                      of tectonic plates.




   Compression
       and
     Tension
• Compression- is the type of stress an object
  experiences when it is being squeezed.
• Tension- is the type of stress that occurs when
  forces act to stretch an object.
• We have established that some rock layers
  cannot withstand the pressure caused by the
  movement of tectonic plates.
   – Fault: a break in a body of rock along which one
     block slides relative to another.
•There are three types of faults:
  •Normal faults: occur when rocks are pulled apart because of
  tension.
  •Reverse faults: occur when rocks are pushed together by
  compression.
• The third type of fault is the strike-slip fault,
  which occurs when rocks are moved
  horizontally by opposing forces.
   – One example of this type is the San Andreas Fault.
• It is at these faults that most earthquakes
  occurs. Seismology or the study of
  earthquakes is a branch of science devoted
  strictly to the study of earthquakes.
        How many earthquakes do you
         think happen every year?
• Following a period of
  deformation, the
  Earth’s crust around
  a fault “bounces”
  back to its original
  shape. This sudden
  return of elasticity is
  called elastic
  rebound.
• Seismic waves: are waves of energy that travel
  through the Earth, away from an earthquake
  in all directions.
  – There are three types of seismic waves.
     • “P” or Primary wave
     • “S” or Secondary wave
     • “L” or Longitudinal wave (a.k.a. surface wave)
• P-wave or Primary Wave
  – Fastest
  – First to be felt
  – Least amount of damage


• S-wave of Secondary Wave
  •Second
  •Slow
  •Side to side motion
  •Limited damage
• L-wave/Longitudinal wave or Surface wave
  – Last
  – Strongest
  – Up and down motion
  – Most damage.

				
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posted:12/17/2011
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