Earthquakes


Earthquakes

 

 

 

Elastic Rebound Theory

 

 

 

 

Focus: where the rocks break

Epicenter: on the Earth's surface directly above the focus

 

 

Types of Waves

 

 

 

 

  • Primary Waves
  • Fastest
  • push/pull or compress waves
  • travel through solids and liquids
    • S Waves
        • Secondary Wave
        • Slower than P Waves
        • Transverse or travel side to side
        • Travel through only solids
    •  L Waves
        • Last Waves
        • Travels on the surface
        • Slowest type of wave
        • Travels up/down or side to side

     

    Measuring Earthquakes

     

    • Mercalli Scale
      • Based on intensity
      • Qualitative and subjective
      • Scale from 1 to 12
      • Measures amount of damage

     

    • Richter Scale
      • Measures magnitude
      • Quantitative
      • Logarithmic

     

     

     

    Effects of Earthquakes

     

    • Damage is dependent on  population density, construction, soil types and rocks
    •  It isn't the earthquake that kills, it is the effects:
        • Buildings collapsing
        • Fires
        • Landslides
        • Tsunamis
        • Liquid faction (when soil and other soft sediment turns to liquid while the Earth is vibrating)

    Predicting Earthquakes

     

     

    • Long-term prediction
        • Based on historical dates of previous earthquakes
        • Measurements of plate movement
        • Can only give vague estimates
        • Distinguish high potential areas from low potential areas

     

     

    • Short-term prediction
        • To pinpoint time and location
        • Almost impossible
        • Seismologists look for signals:
        • Foreshocks
          • Odd Animal Behaviour
          • Changes in land
          • Changes in water table
          • Radon gas detected

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

    One of the most significant earthquakes of all time was The Great 1906 San Francisco earthquake. It was estimated to have a magnitude of 7.8 on the Richter scale.

    Image:Sfearthquake2.jpgThe streets of San Francisco after the devestating earthquake. Enechalon fractures from The Great 1906 San Francisco earthquake.

     

    Types of Earthquakes

    There are two types of Earthquake : Earthquakes take place within the interior of a plate

     

    1.  

      Interplate Earthquakes - Earthquakes that occur in the fault zones at plate boundaries

       

    2. Intraplate Earthquakes - Earthquakes take place within the interior of a plate

     

    InterPlate Earthquake :

    Interplate earthquakes occur along the three types of plate boundaries :

                                                                                                                                    * Ocean spreading ridges 

     

                                                                                                                                    * Subduction zones

     

                                                                                                                                    * Transform faults

     

     

  • Transform faults are places where plates slide past each other horizontally. Strike-slip faults occur there. Earthquakes along transform faults may be large, but not as large or deep as those in subduction zones. One of the most famous transform faults is the San Andreas Fault. The slippage there is caused by the Pacific Plate moving past the North American Plate. The San Andreas Fault and its associated faults account for most of California's earthquakes.

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    Intraplate Earthquake :

    Intraplate earthquakes are not as frequent or as large as those along plate boundaries. The largest intraplate earthquakes are about 100 times smaller than the largest interplate earthquakes. Intraplate earthquakes tend to occur in soft, weak areas of plate interiors. Scientists believe intraplate quakes may be caused by strains put on plate interiors by changes of temperature or pressure in the rock. Or the source of the strain may be a long distance away, at a plate boundary. These strains may produce quakes along normal, reverse or strike-slip faults.

    Earthquakes can be further broken down and classified as: tecotonic, volcanic, and explostion. 
    Tectonic earthquakes - These occur when rocks in  the earth's crust break due to geological forces created by movement .
    Volcanic earthquakes -  Earthquakes that result from tectonic forces which occur in conjunction with volcanic activity.
    Collapse earthquakes - Are small earthquakes in underground caverns and mines.
    Explosion earthquakes - Result from the explosion of nuclear and chemical devices.