Earthquakes by CF2084S

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									Earthquakes
                    Objectives
Given information on Earthquakes, you will be able to
  describe, in writing:

  a) what an earthquake is;

  b) what the elastic rebound theory is;

  c) how earthquakes are measured;

  d) how earthquakes are related to plate tectonic theory;

  e) hazards associated with earthquakes; and

  f) the significance of studying earthquakes.
             Earthquakes
Definition:
An earthquake (also known as a tremor or
 temblor) is the result of a sudden release
 of energy in the Earth's crust that creates
 seismic waves.
                          Earthquakes
Elastic Rebound Theory
• explanation for how energy is spread during earthquakes

• plates/blocks of earth shift on opposite sides of a fault

• these are subjected to force (Time 1)

• they accumulate energy (Time 2)

• they slowly deform until their internal strength is exceeded

• a sudden movement occurs along the fault

• accumulated energy is released

• rocks snap back to their original undeformed shape (Time 3)
                  Earthquakes
Measurement

1. Magnitude scale
   a) measures energy released;
   b) an earthquake one number higher is approximately 30
   times more powerful (e.g. a 7.0 vs. a 6.0); (the scale is
   logarithmic)
   d) an earthquake one number higher produces
   approximately 10 times more ground shaking
   e) examples = Moment Magnitude, Richter
                  Earthquakes
Measurement (cont.)

2. Mercalli Intensity scale
   a) measures intensity or damage of an earthquake;
   b) quantifies the effects of an earthquake on the Earth's
   surface, humans, objects of nature, and man-made
   structures
   d) scale ranges from I through XII, with I denoting a
   weak earthquake and XII one that causes almost
   complete destruction
   e) based on the amount of resulting physical damage
   received
   f) data is gathered from individuals who have
   experienced the quake
              Earthquakes
Plate Tectonics
• Earthquakes are NOT randomly distributed
  across the globe
• They are concentrated along narrow zones
• Most earthquakes (~80% or more) occur along
  plate boundaries
• Interior of plates are mostly earthquake free
• Earthquakes define plate boundaries
• Some also occur at Hot Spots
            Earthquakes
Hazards
1. Ground motion
2. Liquefaction
3. Landslides & mass wasting
4. Tsunamis
          Ground Motion




Ground motion simulation map from the 1906 SF Earthquake
Liquefaction
Landslides & Mass Wasting
Tsunamis
             Earthquakes
Significance
• It is important to study earthquakes due to
  the loss of life and damage to property
  they can cause
• Human population continues to grow and
  many cities are cited along plate
  boundaries
• Education is the key to being prepared for
  earthquakes
                Summary
• Earthquakes occur due to the elastic rebound
  theory
• Earthquakes are measured using the magnitude
  scale
• Earthquakes occur along plate boundaries
• Earthquakes cause ground motion, tsunamis,
  mass wasting, and liquefaction
• Earthquake hazards may cause loss of life and
  damage to property

								
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