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Intensity and magnitude

• An earthquakes intensity refers to the effects
  it causes. It is a subjective value measured by
  the Mercalli scale.

• The magnitude of an earthquake is a measurement
  of how much energy it releases. It is an
  objective value measured by the Richter scale.

The Mercalli scale
The Richter scale
Table summarising the scales and observed damage
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The Mercalli scale

• The Mercalli scale is used to measure the
  intensity of an earthquake.

• It has 12 degrees.

• The lower degrees of the scale deal with how the
  earthquake is felt by people, while the higher
  levels are related to observed structural damage
  (collapsed buildings, roads, etc.).

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The Richter scale

• This scale measures the magnitudeof an
  earthquake.

• It is a logarithmic scale (for each whole number
  increase on the scale, 32 times more energy is
  released). It has no upper limit.

• The Richter scale assigns a numeric value to the
  energy an earthquake releases.

• The most devastating earthquakes measure about 9
  on the Richter scale. The earthquake that hit
  Japan in 2011, for example, had a magnitude of
  8.8 on the Richter scale.

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EARTHQUAKE CLASSIFICATION SCALES AND DAMAGE OBSERVED EARTHQUAKE CLASSIFICATION SCALES AND DAMAGE OBSERVED EARTHQUAKE CLASSIFICATION SCALES AND DAMAGE OBSERVED
RichterMagnitude MercalliIntensity Witness Observations
lt 3 I-II Hard to detect.
3-4 II-III Vibrations similar to the passing of a lorry are felt.
gt4-5 IV-V Small objects are overturned. Some people who are sleeping wake up.
gt5-6 VI-VII It is difficult to stand. There is damage to brick structures.
gt6-7 VII-VIII General alarm. Some walls may fall.
gt7-8 IX-XI Massive destruction. Large landslides.
8-9 XI-XII Total destruction. The ground moves in waves.
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