Earthquake Frequency

Earthquake Frequency. Part of the Exploring Earth Using Seismology poster. HOW OFTEN DO EARTHQUAKES OCCUR?
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Large earthquakes occur about once a year. Smaller earthquakes such as magnitude 2 earthquakes, occur several hundred times a day. To create a mountain system might take several million medium size earthquakes over tens of millions of years.
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We describe the size of an earthquake using the extended Richter Magnitude scale, shown on the left hand side of the figure. The larger the number, the bigger the earthquake. The scale on the right hand side of the figure represents the amount of high explosives required to produce the energy released by the earthquake.
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The 1994 earthquake in Northridge, California, for example, was about magnitude 6.7. Earthquakes this size occur about 20 times each year worldwide. Although the Northridge earthquake is considered moderate in size, it caused over $20 billion in damage. The earthquake released energy equivalent to almost 2 billion kilograms of explosives, about 100 times the amount of energy that was released by the atomic bomb that destroyed the city of Hiroshima during World War II.

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