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Earthquakes Definition: Earthquakes occur when the Earth's plates rub beside one another. When this occurs, vibrations are caused and sometimes releases stress, such as eruptions from volcanoes (For information about volcanoes, go to the volcanoes page.)
Richter Scale: The Richter scale measures the magnitude of earthquakes. American geologist, Charles W. Richter, created the Richter Scale.
Mercalli Scale: The modified Mercalli Scale measures the intensity of an earthquake. This is just the opposite of the Richter Scale. This Mercalli Scale uses the effects on people and buildings to determine the intensity.
Fun Fact: The magnitude of San Francisco's 1906 earthquake according to the Richter Scale was 8.3. This earthquake lasted only 75 seconds. In October 1989, the earthquake that hit San Francisco had a magnitude of 7.1 on the Richter Scale.
The Richter Scale
| Magnitude |
Possible effects |
| 1 |
only noticed by devices |
| 2 |
barely noticable |
| 3 |
Felt indoors |
| 4 |
noticed by most peoples;slight damage |
| 5 |
everyone notices; little damage to moderate damage |
| 6 |
Moderately destructive |
| 7 |
Lots of damage |
| 8 |
Extreme damage |
The Modified Mercalli Scale
| Intensity |
Effects |
| I |
felt by few |
| II |
few sleeping people notice; suspended objects may sway |
| III |
Felt indoors; might not be reconized as eathquake; cars may rock slightly |
| IV |
many feel indoors; few feel outdoors; household items may be disturbed; walls creak; cars rock noticiably |
| V |
practially everyone feels; household utensils could be broken; tall objects (trees, poles, etc.) may be disturbed |
| VI |
all notice; heavy furniture might move; slight damage |
| VII |
everyone runs outdoors; damage might be noticialbe; chimneys broken; moving vehicles might notice |
| VIII |
slight damage; buildings might partically collaspe; furniture overturned; moving cars disturbed |
| IX |
Buildings shift off foundation; ground cracks; pipes break |
| X |
Well-built wooden buildings collaspe; rails bent; landslides |
| XI |
few buildings stay standing; bridges in ruin; pipelines out of service; rails bend lots |
| XII |
Great toll; objects in air |
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