The Richter Scale: Measuring the Magnitude of Earthquakes

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Scientists measure earthquakes using the Richter scale. This scale, invented in 1934 by California scientist Charles Richter, measures the magnitude of an earthquake, and the result is a number from 0 to 10, as measured on a machine called a seismograph.

The scale is not a normal number scale, however; rather, it is a logarithmic scale. This means that an earthquake that measures 2 on the Richter scale is 10 times as powerful as an earthquake that measures 1. In addition, each whole number increase means 32 times more energy is released.

The Richter scale measures earthquakes in whole numbers and tenths numbers. Most earthquakes register 2.5 or less and are too small to be experienced by people. Seismographs register these quakes, though.

Scientists estimate that 900,000 of such "small" quakes occur every year. Up to 30,000 of quakes measuring 2.5 to 5.4 occur in a year as well, and these cause minor damage and are certainly noticed by people. The higher the number on the Richter scale, the fewer earthquakes occur every year. Quakes registering 8.0 or higher occur, on average, only once every 5 to 10 years.

The classes of earthquakes, according to the United States Geological Survey, are these:
Class Magnitude
Great 8 or more
Major 7 - 7.9
Strong 6 - 6.9
Moderate 5 - 5.9
Light 4 - 4.9
Minor 3 -3.9

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