An
earthquake is the result of a sudden release of energy in the Earth''s
crust that creates seismic waves. Earthquakes are recorded with a seismometer,
also known as a seismograph. The moment magnitude of an earthquake is
conventionally reported, or the related and mostly obsolete Richter magnitude,
with magnitude 3 or lower earthquakes being mostly imperceptible and magnitude
7 causing serious damage over large areas. Intensity of shaking is measured on
the modified Mercalli scale.
At the Earth''s surface, earthquakes manifest themselves by a shaking and
sometimes displacement of the ground. When a large earthquake epicenter is
located offshore, the seabed sometimes suffers sufficient displacement to cause
a tsunami. The shaking in earthquakes can also trigger landslides and
occasionally volcanic activity.
In its most generic sense, the word earthquake is used to describe
any seismic event—whether a natural phenomenon or an event caused by
humans—that generates seismic waves. Earthquakes are caused mostly by rupture
of geological faults, but also by volcanic activity, landslides, mine blasts,
and
nuclear experiments.
More abstracts about the earthquake