Earthquakes – Chapter 6

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					Earthquakes – Chapter 6
      Elastic Rebound Theory
• Rocks on either side
  of a fault move slowly
• When locked, stress
  builds…until fault
• Rocks fracture and
  slip to new position
  releasing vibrations -
  create seismic waves
Relaxed   Stressed   Released
            What are faults
• A fault is a crack in the Earth's crust along
  which movement has occurred.
• Occur at plate boundaries or within a plate
• Consists of a
   hanging wall (HW)
  and a
  foot wall (FW)
          3 types of faults
• Normal:
  – at divergent boundaries, HW moves
    down, FW moves up
• Reverse (or thrust fault):
  – at convergent boundaries: HW moves
    up, FW moves down
• Strike-slip faults:
  – At transform boundaries; movement is
     San Andreas Fault

Strike-slip fault
     From shuttle (above)
     From air (at right)
More San Andreas
         Earthquake Vocab
• Focus: area along
  fault where
  slippage 1st occurs

• Epicenter: point on
  surface directly
  above the focus
Major EQ Zones – 1. Ring of Fire
2. Mid-Ocean Ridges
3. Eurasian-Melanesian Mts

  Boundary of Eurasian-Indian-African plates
              4. Fault Zones
• Faults along plate
  boundaries – San
  Andreas strike-slip
• Faults within plates –
  in middle of US -
  1812 New Madrid,
  Missouri EQ
• New England, too?
• Nov. 2006 NH – 1.2
           Recording EQs
• Seismograph:
  instrument used
  to record EQs

• Seismogram:
  printout from a
              Types of Seismic Waves
• Primary “P”
• Secondary “S”
• Surface Waves
  – Rayleigh “R”
  – Love “L”
         Primary “P” waves
• “push-pull” waves
• Fastest seismic waves; 1st to be recorded
• Compression waves (like sound)
• Cause movement in the same direction as
  the wave motion
• Rocks vibrate backwards and forwards,
• P waves can travel through liquids and
       Secondary “S” waves
• Shake or shear waves
• Second to be recorded
• Slower and more destructive than P waves
• Rocks are moved from side to side as the
  wave passes, moving at right angles to the
  direction of wave motion
• Transverse waves, like water waves
• Move through solid only
             Surface, “L” waves
• L for “Love” waves
• Slowest of the three EQ wave types
• L waves take the longer surface route around the
• Have a rolling motion, side to side
• Cause great damage
• Behaves most like waves in a pond or on the sea
                    Other surface waves
• Rayleigh waves
• Rolls along the ground, moving ground up
  and down
•   Animation:
Power and ground type

•The type of rock will determine how fast
the wave travels, and will thus affect
amplitude of the waves
   Using Seismic Waves to determine
            Earth’s Interior
• P waves travel
  through solids,
  liquids and
• S waves travel
  through solids
• Outer core
  must be liquid
  (no S waves
         Earthquakes, Tsunami and
• Read and take notes – pp 104-105
• Answer questions #1-4, pg 102 and
  #3-5, pg 105

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