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Earthquakes
Factfile |
 Earthquakes |
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How Earthquakes Are Measured
There are a number of ways Seismologists (scientists who study earthquakes) measure an earthquake. Probably, the most famous is the Richter Scale - named after Charles F. Richter (1900-1985), an American Seismologist. Charles Richter devised a way of measuring how big an earthquake was by measuring the strength of its shock waves. The bigger the earthquake, the higher the number on the Richter Scale - which he devised to be an open-ended scale.
Part of the Richter Scale is shown below:
| Richter Scale | Effects of shocks | Average no. of quakes per year |
| Under 3.4 | Recorded, but not felt | over 10 million |
| 4.9 - 5.4 | Felt by everyone | 1500 |
| 7.0 - 7.3 | Serious damage | 15 |
| Over 8 | Nearly total damage | 0.1 - 0.2 |
The most serious earthquakes are in the range of 5 to 9. The earthquake in San Francisco in 1906 was valued at 8.6. When it comes to understanding about the power of earthquakes and the damage they can cause, it is important not to just consider the Richter Scale reading - it is about where it hits and how weak or strong the buildings are.
The biggest earthquake ever, was probably the quake in New Madrid, Missouri, USA in 1812. The first quake happened on 16th December 1811 and then carried on shock after shock, until February 1812. Not only did the shock waves of these quakes travel as far as Washington DC, a 1000 km away, the Mississippi River was changed in several places as a new landscape was produced.
China on the other hand, has had some of the world's worst earthquakes. In 1920, about 180,000 people were killed in Gansu, China. Then in 1976, the city of T'ang-shan (population 1.6 million) was virtually wiped out.
The largest ever-recorded earthquake on the Richter Scale was in 1960 in Lebu, Chile and measured 9.5. The probable death toll from this earthquake is unknown.
Probably the earthquake that most people have heard of, is the severe earthquake that struck San Francisco, USA on the 18th April 1906. The quake lasted less than a minute and reduced the city to ruins. It also killed 700 people and caused over $1,000 million of damage.
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