Seismicity: The Causes of Earthquakes

Refers to AQA A2 Geography

Plate Tectonics and Assosiated Hazards Option

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  • Created by: Bethany
  • Created on: 29-04-14 17:58
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  • The Causes of Earthquakes
    • The Process
      • The crust if the earth us mobile so there is a build-up of stress within the rocks
        • Pressure is suddenly released
          • Causes parts of the earth's surface to experience intense shaking motion which lasts for a few seconds.
    • The Focus and Epicentre
      • The point at which the pressure release occurs within the crust is known as the FOCUS
        • The point on the earth's surface immediately above the focus is known as the EPICENTRE (where the earthquake is felt)
        • The depth of the FOCUS is significant...
          • SHALLOW FOCUS (0-70km deep)
            • Tend to cause the greatest damage and account for 75% of all earthquake energy released
          • INTERMEDIATE FOCUS (70-300km deep)
          • DEEP FOCUS (300-700km deep)
        • Pressure is suddenly released
          • Causes parts of the earth's surface to experience intense shaking motion which lasts for a few seconds.
    • Seismic Waves
      • Radiate from the focus like ripples in water when a stone is thrown into a pond
        • There are three types of seismic waves...
          • PRIMARY (P) WAVES
            • Travel fastest and are compressional, vibrating in the direction of travel
          • SURFACE (L) WAVES
            • Travel slowest and near to the ground surface.
            • Some surface waves shake the ground at right angles to the direction of wave movement and sometimes have a rolling motion producing vertical ground movement.
          • SECONDARY (S) WAVES
            • Travel at half the speed of P Waves and shear rock by vibrating the direction of travel,

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