OUR ACTIVE EARTH
Earth is an ever-changing planet. Some changes happen in a matter of seconds or minutes. Other changes occur over months or years. Some changes that take place over hundreds, thousands, and millions of years are erosion and mountain building. On the other hand, changes due to an earthquake happen suddenly and violently.
As you learned before, California is one area where earthquakes are likely to occur. During the past 30,000,000 years, many thousands of earthquakes have occurred along the San Andreas Fault. This fault line is 720 miles long!
Sometimes, the aftershock of the earthquake is just as violent or even more violent than the principal or main shock.
If you’ve ever heard news about an earthquake, you’ve probably heard about the Richter scale. The Richter scale uses numbers ranging from 1 to 10. These numbers measure the magnitude of an earthquake. The magnitude is the strength of the earthquake or the amount of energy that is released.
Richter Magnitudes Earthquake Effects
Less than 3.5
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Generally not felt, but recorded.
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3.5-5.4
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Often felt, but rarely causes damage
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Under 6.0
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Can cause major damage to poorly constructed
buildings over small regions.
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6.1-6.9
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Can be destructive in areas up to about 100
kilometers across where people live
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7.0-7.9
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Major earthquake. Can cause serious damage over larger areas.
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8 or greater
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Great earthquake. Can cause serious damage in areas several hundred kilometers across.
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