An earthquake is a sudden movement of the earth. The ground shakes as a result of the breaking and shifting of rock under great pressure. The vibrations caused by this shaking can cause deaths and severe property damage. An earthquake can trigger a tsunami (tidal wave).
The cause of earthquakes is the movement of the plates of the earth's crust as a result of increased pressure in the mantle beneath the crust. Scientists used to believe that earthquakes were caused by faults, but they now believe that faults in the crust are the damage which results from previous movement in the earth's mantle below the crust. Scientists who study earthquakes are called seismologists.
Seismologists have developed methods for measuring the magnitude (size) and intensity (amount of shaking and damage) of an earthquake. The most familiar earthquake measurement technique is the Richter scale, devised by American seismologist Charles Richter (1900-1985), which measures the force of the earthquake. The scale begins at about 2.5 and ranges to 8 or 9, based on earthquakes measured by instruments and calculated by his formula. The intensity of an earthquake as felt by the people living in the quake area is measured by the Modified Mercalli Intensity Scale.
Seismologists also try to anticipate and predict where an earthquake will strike. They use instruments set into the earth called seismographs, which measure vibrations in the earth. As the vibrations increase, seimologists can issue warnings.
Web Sites
- National Oceanic and Atmospheric Administration (NOAA)
- National Geophysical Data Center (NOAA)
- Plate Tectonics (University of Nevada Seismology Department)
Web Sites For Kids
Catalog
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See also: tsunami
Databases
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