1. UNIT 7 The Earth’s dynamics Natural Science 2. Secondary Education HOW AN EARTHQUAKE’S STRENGTH IS MEASURED

2. UNIDAD 3 UNIT 7 How 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 scaleThe Richter scale Table summarising the scales and observed damage

3. UNIDAD 3 UNIT 7 How 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

4. UNIDAD 3 UNIT 7 How 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 magnitude of 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

5. UNIDAD 3 UNIT 7 How an earthquake’s strength is measured Natural Science 2. Secondary Education EARTHQUAKE CLASSIFICATION SCALES AND DAMAGE OBSERVED Richter Magnitude Mercalli Intensity Witness Observations < 3I-IIHard to detect. 3-4II-III Vibrations similar to the passing of a lorry are felt. >4-5IV-V Small objects are overturned. Some people who are sleeping wake up. >5-6VI-VII It is difficult to stand. There is damage to brick structures. >6-7VII-VIIIGeneral alarm. Some walls may fall. >7-8IX-XIMassive destruction. Large landslides. 8-9XI-XII Total destruction. The ground moves in waves. Go back to the start menu