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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 Kôbe, Japan (magnitude 6.8), occur about 20 times a year.
In the last 500 years, earthquakes around the world have killed several million
people including over 240,000 in the 1976 T’ang-Shan, China, earthquake.
Worldwide, earthquakes have also caused severe property and structural damage.
Adequate precautions, such as education, emergency planning, and constructing
stronger, more flexible, safely designed structures, can limit the loss of life
and decrease the damage caused by earthquakes.
