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Measuring Earthquake Magnitude

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The Magnitude of Magnitude
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The Magnitude of Magnitude


Credit: Unknown
Source: http://en.wikipedia.org/wiki/File:1755_Lisbon_earthquake.jpg
License: CC BY-NC 3.0

This engraving shows Lisbon, Portugal in flames and being inundated by tsunami after the November 1, 1755 earthquake. There were no seismographs around, so the magnitude is estimated to have been between 8.5 and 9.0.

Why It Matters

  • Earthquake magnitude measures the energy it releases.
  • Magnitude is measured on an exponential scale: a gain in one whole number is an increase of 33-times the amount of energy released.
  • The Richter Magnitude scale measures the amplitude of the largest wave (shaking amplitude). Each whole number increase in shaking amplitude is a factor of 10.
  • Credit: U.S. Department of the Interior | U.S. Geological Survey
    Source: http://earthquake.usgs.gov/learn/glossary/?termID=149
    License: CC BY-NC 3.0

    Richter magnitude scale developed in 1935 to estimate the size of earthquakes [Figure2]


  • As scientists refine numbers, a reported earthquake magnitude may change.
  • These days, earthquake magnitudes are reported on the Moment Magnitude Scale.

Can You Apply It?

With the links below, learn more about earthquake magnitude. Then answer the following questions.

  1. In the video, the difference from one magnitude to the next is 33-times. Which scale are they using?
  2. How much more energy is released by an earthquake that is three whole numbers bigger than another earthquake? Show the math.
  3. In the video, on the image with circles for earthquake magnitudes, a 9.5 in Chile is the largest quake. Where is the 5.8 in Virginia on that image? Why?
  4. The 1755 Lisbon earthquake is estimated to have been between magnitude 8.5 and 9.0. How many times more energy would be released if it were 9.0 than 3.5?

Image Attributions

  1. [1]^ Credit: Unknown; Source: http://en.wikipedia.org/wiki/File:1755_Lisbon_earthquake.jpg; License: CC BY-NC 3.0
  2. [2]^ Credit: U.S. Department of the Interior | U.S. Geological Survey; Source: http://earthquake.usgs.gov/learn/glossary/?termID=149; License: CC BY-NC 3.0


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