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Extra!: Earthquakes

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(CNN Student News) -- Earthquake magnitude, determined by seismograph, is the measure of the energy that an earthquake releases at its source. An earthquake's intensity level is a measurement of how much it shakes and the damage it inflicts. Here is a breakdown of descriptions and the annual frequency of earthquakes by magnitude, based on observations made since 1900.

Intensity: 8 +

Damage levels can be slight in earthquake-proofed buildings, considerable in ordinary substantial buildings and devastating in poorly built structures. At this category's most intense level, no masonry or wooden structures remain standing and bridges might collapse. Lines of sight can be distorted.

  • Description: Great
  • Frequency: 1
  • Intensity: 7 - 7.9

    Depending on the design and construction of a building, damage can range from slight to devastating. At this category's most intense level, no masonry or wooden structures remain standing. Bridges can be destroyed. Lines of sight can be distorted and objects can be thrown into the air.

  • Description: Major
  • Frequency: 18
  • Intensity: 6 - 6.9

    Depending on the design and construction of a building, damage can range from negligible to considerable with a structure's partial collapse. Buildings might shift off their foundations. Monuments, walls and chimneys can fall, and heavy furniture may overturn.

  • Description: Strong
  • Frequency: 20
  • Intensity: 5 - 5.9

    Heavy furniture can move and plaster can fall. Depending on the design and construction of a building, damage ranges from negligible to considerable. Chimneys might break.

  • Description: Moderate
  • Frequency: 800
  • Intensity: 4 - 4.9

    Most people can feel this level indoors as a sensation as strong as a heavy truck hitting the building. People who are asleep may wake up. Dishes and windows can be disturbed or broken. Walls may make cracking sounds. Parked cars may rock. Some unstable objects may overturn.

  • Description: Light
  • Frequency: 6,200
  • Intensity: 3 - 3.9

    Parked cars might rock slightly. The quake's vibrations feel like a passing truck.

  • Description: Minor
  • Frequency: 49,000
  • Intensity: 2 - 2.9

    Only a few people at rest, especially in the upper floors of buildings, will feel this level of a quake.

  • Description: Very Minor
  • Frequency: 52,000
  • Intensity: 1 - 1.9

    This level of earthquake is usually not felt, except by very few people.

  • Description: Very minor
  • Frequency: 416,000
  • (Sources: CNN.com, U.S. Geological Survey)


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