An earthquake is an event when 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 constant movement of the plates
of the earth's crust as a result of pressures building
up 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
resulting from movement in the earth's mantle below the
crust.
The two difficulties scientists have had are establishing
a method for measuring the magnitude and intensity of
the earthquake, and finding a way to predict where and
when a severe earthquake will occur so that the population
of that location can be prepared for it. The measurement
method most people are familiar with is the Richter scale,
devised by American seismologist Charles Richter (1900-85),
which measures the magnitude of the quake. It has
started at about 2.5 and goes to 8 or 9, based on earthquakes
measured by instruments and calculated by his formula
to date. The intensity of an earthquake as felt
by people in the area of the quake is measured by the
Modified Mercalli Intensity Scale.
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
Search the library's catalog for earthquakes, natural disasters, seismology.
See also: tsunami
Databases
Enter earthquake in these databases: