unit 7 the earth’s dynamics natural science 2. secondary education how an earthquake’s strength...
TRANSCRIPT
UNIT
7The Earth’s dynamics
Natural Science 2. Secondary Education
HOW AN EARTHQUAKE’SSTRENGTH IS MEASURED
UNIDAD
3UNIT
7How an earthquake’s strength is measured
Natural Science 2. Secondary Education
Intensity and magnitude
• An earthquake’s 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.
Click on each box to find out more.
The Mercalli scale The Richter scale
Table summarising the scales and observed
damage
UNIDAD
3UNIT
7How an earthquake’s strength is measured
Natural Science 2. Secondary Education
• It has 12 degrees.
The Mercalli scale
• 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.).
• The Mercalli scale is used to measure the intensity of an earthquake.
Go back to the start menu
UNIDAD
3UNIT
7How an earthquake’s strength is measured
Natural Science 2. Secondary Education
• The Richter scale assigns a numeric value to the energy an earthquake releases.
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 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.
Go back to the start menu
UNIDAD
3UNIT
7How an earthquake’s strength is measured
Natural Science 2. Secondary Education
EARTHQUAKE CLASSIFICATION SCALES AND DAMAGE OBSERVED
RichterMagnitude
MercalliIntensity
Witness Observations
< 3 I-II Hard to detect.
3-4 II-IIIVibrations similar to the passing
of a lorry are felt.
>4-5 IV-VSmall objects are overturned. Some people
who are sleeping wake up.
>5-6 VI-VIIIt is difficult to stand. There is damage to brick
structures.
>6-7 VII-VIII General alarm. Some walls may fall.
>7-8 IX-XI Massive destruction. Large landslides.
8-9 XI-XIITotal destruction. The ground
moves in waves.
Go back to the start menu