Earthquakes and Earthquake Hazards by tiw14488

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									 Earthquakes and
Earthquake Hazards
   Describing Broken Rocks
Joint – a crack along which little motion
 has occurred.
  • common feature of all rocks
  • result of tectonics and burial/erosion




    Fig. 11.6
  Describing Broken Rocks
Fault – crack along which movement has
 occurred.
  • far less common than joints
  • result mainly from tectonics




                   Fig. 11.8
     Describing Fault Motion

Direction of motion
  along a fault
  related to stress
  type (comp.,
  tension, shear).
Identify “footwall”
  and “hanging wall”
                       Fig. 11.7
  sides of fault.
     Describing Fault Motion
Normal faults – footwall moves up with
 respect to hanging wall.
Formed by tensional stresses.




                            Fig. 11.8
     Describing Fault Motion
Reverse and thrust faults – footwall moves
 down with respect to hanging wall.
Formed by compressional stresses.




          Fig. 11.8                  Fig. 11.8
     Describing Fault Motion
Strike-slip faults – horizontal movement,
  little or no vertical movement.
Formed by shear stresses.




                                      Fig. 11.8
               Fig. 11.8
What type of fault is this?



    Hanging wall



                   Footwall
     Elastic Rebound Theory

1. No stress, undeformed.

2. Shear stress applied, elastic
  deformation, energy stored.

3. Stress exceeds strength,
  brittle failure, stored energy
  released as seismic waves.

4. Stress released, undeformed.
                                   Fig. 11.31
     Earthquake Frequency
Yearly - many small earthquakes, few
 large ones




                                Fig. 11.34
     Measuring Earthquakes
Richter Scale
  • based on measurement
    of energy released
    during quake
  • calculated based on
    distance from
    earthquake to recording
    station, and height of
    surface wave
                              Fig. 11.34
     Measuring Earthquakes
Most earthquakes occur below the surface.
Fault scarp created when rupture extends
 to the surface (a rare event).


                                    Fault scarp




                       Fig. 11.28
          Fig. 11.29
    Measuring Earthquakes
Modified Mercalli Intensity Scale
 • based on extent felt by people,
   damage to structures, secondary
   effects (landslides, tsunamis)
      Earthquake Hazards
Damage to structures is dependent upon:
  • earthquake magnitude.
  • geologic materials.




                       Fig. 11.37
      Earthquake Hazards
Damage due movement of surface
 waves.
Surface waves higher in wet mud than
 solid rock.




                             Fig. 11.38
      Earthquake Hazards
Liquefaction – when sediments behave
  like a liquid during an earthquake.
   • causes foundation failures
  Assessing Seismic Hazards
Earthquakes currently can’t be predicted.
Hazard maps predict where greatest ground
 shaking will occur.
  • modify building codes to resist shaking




      Fig. 11.38
             Tsunamis
Generated primarily by submarine
   earthquakes.
If the sea floor is displaced, waves may
   be generated.
Waves can travel at 100s km/hr, and
   travel for 1000s of km.
Destruction occurs by flooding of coastal
   lowlands.
Generation and Movement of a
          Tsunami
2004 Indian Ocean Tsunami




   Animation

								
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