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Earthquakes

An earthquake is a sudden slipping or movement of a portion of
the Earths crust or plates, caused by a sudden release of stresses.  Earthquake
epicenters are usually less than 25 miles below the Earths surface
and are accompanied and followed by a series of vibrations.

The reason that earthquakes are
such a risk is because shaking ground can: 

Cause buildings to move off of their foundations
or collapse.


Damage utilities, structures, and roads.


Cause fires and explosions.



Cause structural instability, such as dam failures that can trigger
flash floods.

Earthquakes can also trigger
landslides and avalanches or tsunamis.  After an earthquake, it
is important to listen for emergency instructions.

Together, all of these
types of damage threaten lives, property, and the environment.

The greatest likelihood of a major earthquake is in:

The Western United States, particularly along the
San Andreas Fault in California and up the Alaskan coast.


The New Madrid Fault Zone in Missouri.


A few pockets on the east coast.

Some statistics about earthquakes
include:

Fifteen percent of the population lives in the zones of potential
major disaster.


Californias 17 million people face the highest risk,
followed by the residents of Washington State.


Four million people are within the destructive reaches
of the New Madrid Fault.


Residents of Massachusetts, North Carolina, and South
Carolina are also at risk.







Earthquakes
(Continued)

Hundreds of tremors are felt
each year, particularly in California.  Major earthquakes are rare,
however.  Five major earthquakes have occurred in the last century
in the United States.  They occurred in:

San Francisco, 1906 (2,000 lives lost).


Alaska, 1964 (131 lives lost).


San Fernando, California, 1971 (65 lives lost).


Loma Prieta (Northern California), 1989 (66 lives
lost).


Northridge (Southern California), 1994 (61 lives
lost).

There is no seasonal or yearly
cycle of earthquake occurrence; earthquakes can happen at any time. 
Major earthquakes appear to occur in cycles of between 50 and 275 years. 
It is likely that an earthquake will hit California and perhaps other
parts of the United States in the next decade or two.

An earthquake may last
for seconds or minutes, while aftershocks may occur for months after
the main earthquake.

Earthquakes are classified, based
on the Richter Scale, as:

Small:  5.0-5.9.


Moderate:  6.0-6.9.


Major:  7.0-7.9.


Great:  8.0 or greater.

The Richter Scale has a logarithmic
base, so each increment on the scale is multiplied by a factor of 10. 
For example, an earthquake of magnitude 8.6 would not be twice as violent
as one of 4.3, but rather would be 10,000 times worse.

Earthquakes
(Continued)
Earthquake Safety

It is recommended that you:

Develop a home earthquake plan so that you know what to do
during and after an earthquake.


Conduct earthquake drills with your family or coworkers. 
Locate safe spots (e.g., under a sturdy table), and identify danger
zones (e.g., near windows).


Develop a plan for reuniting all family members after an earthquake
occurs.


Identify an out-of-state contact for family members to phone.


Keep supplies on hand, including food and water for 3 days,
a flashlight with extra batteries, a portable radio, a fire extinguisher,
and tools.