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Measuring the size of Earthquakes

Earthquakes happen all over the world. In the UK they are rarely felt and even then many only perhaps rattle cups in the cupboard but not much more. They may be caused by subsidence when old mine-workings are nearby.

Some parts of the world get earthquakes quite regularly, especially around the rim of the Pacific ocean in places such as the west coasts of North and South America, the east coast of China, Japan and New Zealand, where they can often be very severe, toppling buildings and bringing down bridges.

They are measured on the Richter Scale, invented by Charles Richter in 1935. He was an American seismologist (a scientist who studies earthquakes). Each number represents a ten-fold increase in the energy released in the earthquake. So a magnitude 2 earthquake was 10 times as powerful as a magnitude 1; a magnitude 3 was 100 times as powerful as a magnitude 1 earthquake and so on. Such scales are called logarithmic.

    The Richter Scale
  1. Too small to feel and measured by instruments only.
  2. Felt by sensitive people and some animals.
  3. Feels like a truck passing by.
  4. Felt by everyone; pictures fall off the wall.
  5. Damage - may cause weak walls to crack and fall.
  6. A destructive earthquake in populated areas; chimneys fall off rooves, etc.
  7. A major earthquake causing serious damage.
  8. A disaster. A great earthquake that produces total destruction to nearby communities, for example, the San Francisco earthquake in 1906 measured 8.3 on the richter scale.
  9. Lisbon, Portugal had the highest ever in 1775 at 8.9.