Nov
18
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November 18, 2009 | Tagged Pacific | Leave a Comment
An earthquake is a sudden, rapid shaking of the Earth caused by the breaking
and shifting of rock beneath the Earth’s surface. For hundreds of millions of years,
the forces of plate tectonics have shaped the Earth as the huge plates that form the
Earth’s surface move slowly over, under, and past each other. Sometimes the
movement is gradual. At other times, the plates are locked together, unable to release
the accumulating energy. When the accumulated energy grows strong enough, the plates
break free causing the ground to shake. Most earthquakes occur at the boundaries where
the plates meet; however, some earthquakes occur in the middle of plates.
Earthquakes are caused by pressure generated by the movement of continental
plates on the mantle of the earth. There is constant pressure on continental plates
to move. When movement comes as a result of the continental pushin, we often
feel it, and we call it an earthquake. Some of the geological activities caused by
plate tetonics include volcanoes, mountain creation, island creation and a
phenomena known as subduction. Earthquakes rarely ever cause the earth
to crack open along a fault line. After the main earthquake aftershocks are
common. An earthquake a small earthquake or tremor that follows a
major earthquake. Aftershocks usually occur within a few days of the main
earthquake becoming less serious over time.
Earthquakes occurred as early as 1177 b.C in China. They have been part
of a myth since the dawn of man. In Greek Mythology, Posseidon was the " god
of the sea " . He controlled , from his sea-domain , the devasting force of the
earthquake. This abililty to summon earthquakes earned Poseidon the nickname
of " Earth Shaker " .
The most destructive earthquake in U.S history was in San Francisco, California.
It caused over 700 deaths. The great Alaskan earthquake in 1964 was twice as
powerful, but less destructive due to low population density of the area struck. It
came in at 9.5 on the Richter scale. In North America the great earthquakes in
1811-1812 occured near New Madrid, Missouri.
Earthquakes most occur on the boundaries between major tetonic plates. The
earth’s surface is broken into a dozen or so major plates and a number of smaller
plates and those plates are moving with respect to each other. In California there
is a major plate boundary between the pacific plate to the west and the North
American plate to the east. The fault that marks the boundary is the San Andreas
fault and that’s where we have some of the largest earthquakes in the continental
United States.
Earthquake damage depends on what area it hits. If an unpopulated region is
struck, there will be low loss of life or property. If it hits a large city, there may
be many injuries and destruction. Most global cities just about tripled their
populations in thelast hundred years, so a major earthquake could collapse
skyscrapers, factories, and power plants. Millions of people could feel the
shock waves, not only the initial tremor, but of the aftershocks, tsunamis,
landslides, floods, and social effects. Buildings with thick, heavy walls do not
resist shock waves very well. Violent earthquakes often cause structures to
collapse, burrying people underneath.Chimneys are often shaken off during
the tremors, and can crash into bystanders or passerbys. Fire and floods are
often the greatest damage occurs. When an earthquake destroys dams high
above a city or valley, it causes floods to sweep down and sweep away
everything in their path.