What is an earthquake?
Ground shaking from
earthquakes can collapse buildings and bridges; disrupt gas, electric,
and phone service; and sometimes trigger landslides, avalanches, flash
floods, fires, and huge, destructive ocean waves (tsunamis). Buildings
with foundations resting on unconsolidated landfill and other unstable
soil, and trailers and homes not tied to their foundations are at risk
because they can be shaken off their mountings during an earthquake.
When an earthquake occurs in a populated area, it may cause deaths and
injuries and extensive property damage.
The Northridge, California,
earthquake of January 17, 1994, struck a modern urban environment
generally designed to withstand the forces of earthquakes. Its economic
cost, nevertheless, has been estimated at $20 billion. Fortunately,
relatively few lives were lost. Exactly one year later, Kobe, Japan, a
densely populated community less prepared for earthquakes than
Northridge, was devastated by the most costly earthquake ever to occur.
Property losses were projected at $96 billion, and at least 5,378
people were killed. These two earthquakes tested building codes and
construction practices, as well as emergency preparedness and response
procedures.
Where earthquakes have
occurred in the past, they will happen again. Learn whether earthquakes
are a risk in your area by contacting your local emergency management
office, American Red Cross chapter, state geological survey, or
department of natural resources. For information on how to protect your
property from earthquakes, please read the "How-To Series"
Earthquakes strike
suddenly, without warning. Earthquakes can occur at any time of the
year and at any time of the day or night. On a yearly basis, 70 to 75
damaging earthquakes occur throughout the world. Estimates of losses
from a future earthquake in the United States approach $200 billion.
There are 45 states and territories in the United States at moderate to
very high risk from earthquakes, and they are located in every region
of the country. California experiences the most frequent damaging
earthquakes; however, Alaska experiences the greatest number of large
earthquakesmost located in uninhabited areas. The largest earthquakes
felt in the United States were along the New Madrid Fault in Missouri,
where a three-month long series of quakes from 1811 to 1812 included
three quakes larger than a magnitude of 8 on the Richter Scale. These
earthquakes were felt over the entire Eastern United States, with
Missouri, Tennessee, Kentucky, Indiana, Illinois, Ohio, Alabama,
Arkansas, and Mississippi experiencing the strongest ground shaking.
Awareness information
Expect aftershocks.
Aftershocks are smaller earthquakes that follow the main shock and can
cause further damage to weakened buildings. After-shocks can occur in
the first hours, days, weeks, or even months after the quake. Be aware
that some earthquakes are actually foreshocks, and a larger earthquake
might occur.
Ground movement during an
earthquake is seldom the direct cause of death or injury. Most
earthquake-related injuries result from collapsing walls, flying glass,
and falling objects as a result of the ground shaking, or people trying
to move more than a few feet during the shaking. Much of the damage in
earthquakes is predictable and preventable. We must all work together
in our communities to apply our knowledge to building codes,
retrofitting programs, hazard hunts, and neighborhood and family
emergency plans.
Emergency Information
The best protection during an earthquake is to get under heavy furniture such as a desk, table, or bench
The greatest danger exists
directly outside buildings, at exits, and alongside exterior walls.
Many of the 120 fatalities from the 1933 Long Beach earthquake occurred
when people ran outside of buildings only to be killed by falling
debris from collapsing walls.
Ground movement during an
earthquake is seldom the direct cause of death or injury. Most
earthquake-related casualties result from collapsing walls, flying
glass, and falling objects.
Danger Zones
Earthquakes occur most
frequently west of the Rocky Mountains, although historically the most
violent earthquakes have occurred in the central United States. All 50
states and all U.S. territories are vulnerable to earthquakes.
Forty-one states or territories are at moderate to high risk.
Help Your Community Get Ready
The media can raise awareness about earthquakes by providing important information to the community. Here are some suggestions:
Publish a special section
in your local newspaper with emergency information on earthquakes.
Localize the information by printing the phone numbers of local
emergency services offices, the American Red Cross, and hospitals.
Conduct a week-long series on locating hazards in the home.
Work with local emergency
services and American Red Cross officials to prepare special reports
for people with mobility impairments on what to do during an
earthquake.
Provide tips on conducting earthquake drills in the home.
Interview representatives of the gas, electric, and water companies about shutting off utilities.
Did You Know
Many people think of
California as "Earthquake Country," but the state with the most major
earthquakes is Alaska. The granddaddy of earthquakes was along the New
Madrid Fault in Missouri where a 3-month long series of quakes in
1811-1812 included three quakes larger than a magnitude of 8. These
quakes were felt over 2 million square miles.
The Richter Scale was
developed by Charles F. Richter in 1935. It is a logarithmic
measurement of the amount of energy released by an earthquake.
Earthquakes with a magnitude of at least 4.5 are strong enough to be
recorded by sensitive seismographs all over the world. In the United
States several thousand shocks of varying sizes occur annually.
The effects of earthquakes
are also measured by the Modified Mercalli Intensity scale. The
intensity of a quake is evaluated according to the observed severity of
the quake at specific locations. The Mercalli scale rates the intensity
on a Roman numeral scale that ranges from I to XII.
The Loma Prieta (northern
California) earthquake of October 1989 registered 7.1 on the Richter
scale and as high as XI on the Mercalli scale.
Courtesy of FEMA
