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Natural Disasters
Definition:
A natural disaster is an event of nature that takes human lives
or destroys property.
Types of natural disaster:
- Weather conditions: Blizzard, Cyclone, Hurricane, Tornado.
- Floods and their prevention.
- Earthquakes.
- Fires and fire prevention.
- Volcanic eruption.
- Outbreaks of disease: Plague, Epidemiology.
Earthquakes
An earthquake is the shaking of the earth's surface caused by
rapid movement of the earth's rocky outer layer. Earthquakes occur when
energy stored within the earth, usually in the form of strain in rocks,
suddenly releases. This energy is transmitted to the surface of the earth
by earthquake waves.
The destruction an earthquake causes depends on its magnitude
and duration, or the amount of shaking that occurs. The size varies from
small, imperceptible shaking to large shocks felt over thousands of
kilometres. Earthquakes can deform the ground, make buildings and other
structures collapse, and create tsunamis (large sea waves). Lives may be
lost in the resulting destruction.
Earthquakes, or seismic tremors, occur at a rate of several
hundred per day around the world. A worldwide network of seismographs
(machines that record movements of the earth) detects about one million
small earthquakes per year. Very large earthquakes, such as the 1964
Alaskan earthquake, which measured 9.2 on the Richter scale and caused
millions of dollars in damage, occur worldwide once every few years.
Moderate earthquakes, such as the 1989 tremor in Loma Prieta, California
(magnitude 7.0 on the Richter scale), and the 1995 tremor in K |