The Richter and Mercalli Scale

Refers to AQA A2 Geography

Plate Techtonics and Assosiated Hazards

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  • The Richter and Mercalli Scale
    • THE RICHTER SCALE
      • A LOGARITHMIC Scale
        • This means that an event measured a 7 on the scale is TEN TIMES GREATER than one measuring 6 on the scale.
      • Energy release is proportional to magnitude.
        • For eact unit increase on the scale, energy released increases approx. 30 times.
      • Past earthquakes on the scale
        • Largest ever measured on scale was Great Chilean Earthquake of 1960, which measured 9.5.
        • Largest ever recorded UK earthquake was 4.8 on the scale, large for the UK but small compared to Haiti Earthquake, for example, with a magnitude of 7.0.
    • THE MERCALLI SCALE
      • Considers both the intensity of an event AND its impact.
        • Level I would be equivelent to two on the the Richter Scale. Detected by seismometers but felt by very few, if any. No damage caused.
          • Comparisons to Richter scale would depend on the location of the earthquake, hence influencing its impacts.
        • The top level is Level XII. This represents total destruction with the ground seen to shake. This would be equivlent to approx 8.5 on the Richter Scale.
          • Comparisons to Richter scale would depend on the location of the earthquake, hence influencing its impacts.
    • WHICH IS BETTER?
      • Problems with the Mercalli Scale.
        • No use in an uninhabited area such as a desert where there is little human damage
        • Statements such as resembling heavy traffic only apply if a person has felt heavy traffic, or what they feel is heavy traffic, which may differ if they live in a rural area.
        • Impacts vary in different areas, so may be multiple values for the same earthquake.
        • Somewhat SPECULATIVE
      • Problems with the Richter Scale
        • Doesn't take into account amount of damage; an earthquake which may cause collosal damage in one place would cause little damage in an uninhabited area.
      • Judgement
        • The Richter Scale allows easy comparisons of earthquakes which are not speculative regardless of location, and is a mathematical calculation, not a rough category.

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