The crust of the earth is made up of seven masses called tectonic
plates. They are in steady motion. Accumulated stress builds up
from the continental plates grinding, sliding or colliding
against or slipping under each other. Pressure is released in a
powerful explosion of energy that fractures the earth's surface,
shakes the ground, causes the ground to roll, liquefies some soil
and generates giant water waves.
When an earthquake will unleash its force remains unpredictable.
Preliminary cracks may send off foreshocks before a main
fracture. These foreshocks can occur months or minutes before
the rapid onset of the earthquake. An earthquake lasts for
seconds or minutes, while aftershocks may occur for months after
the main earthquake.
Powerful and widespread ruptures or shaking ground can cause
buildings to move off their foundations or collapse; damage
utility lines, other structures and roads; set off fires; and
threaten the lives of people and animals. It is the damage to
structures that presents the greatest risks to life and property.
Earthquakes create a trigger for other natural hazards such as
landslides, tsunamis, avalanches, fires and flash floods.
The greatest likelihood of major earthquakes is in the western
United States, particularly along the San Andreas Fault in
California and up the Alaskan Coast, in the New Madrid Fault Zone
in the Midwest, and in a few pockets on the East Coast,
particularly in South Carolina and New England. There is no
seasonal or yearly cycle of occurrence. Earthquakes can happen
at any time. Major earthquakes appear to occur in cycles of
between 50 and 275 years.
How Earthquakes are Measured
The Richter Scale provides a measure of the magnitude of the
earthquake in terms of energy released, measured in equivalent
tons of TNT. Each unit represents a 10-fold energy release.
An earthquake of Richter 2.5 or less is usually ignored. Dishes
rattling and china shaking occur at 3. The Modified Mercalli
Intensity Scale is a more subjective accounting or survey of
behavior and damage based on observation at the site. Depending
on the intensity of ground vibrations, the elasticity of
buildings and structures, and how well structures are connected
to their foundation, falling or collapsing objects and structures
accompany earthquakes. Structural instability, such as dam
failures, can trigger flash floods. Fires have been the greatest
cause of damage in the past. Offshore earthquakes may cause
Preparing for an Earthquake
In addition to precautions outlined in the sections on General
Family Preparedness, Residential Fires and Hazardous Material
Accidents, you need to take the following steps.
- Become familiar with earthquake terms.
- Aftershocks: Tremors that occur in the hours or days
after the initial earthquake shaking is over.
- Epicenter: The place on the surface of the earth
directly above an earthquake's first movement (focus).
- Fault: A fracture in the earth's crust along which
rocks have been displaced.
- Focus: The point beneath the surface of the earth where
the rocks first break and move, beginning the
- Intensity: An indication of an earthquake's apparent
severity at a specific location, based on its effects
on people and structures.
- Magnitude: Size of an earthquake determined from the
size of the seismic waves it generates as recorded by
- Mercalli Scale: The scale used to measure the strength
of an earthquake as determined by people's eyewitness
- Tidal wave: This is a misnomer for a tsunami. Tidal
waves occur from the interaction of the moon and large
bodies of water. Waves you see rolling into the ocean
shore every day are tidal waves.
- Tsunami: A seismic sea wave. An unusually large wave
(or series of them) produced by an undersea earthquake
or volcanic eruption.
- Safeguard your home by:
- Bolting bookshelves, water heaters and cabinets to wall
- Anchoring things so that they will not move or fall
during an earthquake is the most important thing you
can do to make yourself safe. Keeping things in place
also means they will not break.
- There are many ways to make the contents of your home and
workplace less hazardous.
- Move cabinets and tall furniture so that if they fall
they are not likely to hit people.
- Use steel angle brackets to anchor them to studs in the
- Put heavy or breakable things on bottom shelves. You
can even put "fences" or restraining wires to keep
items from falling off open shelves.
- Put child-proof or swing-hook latches on bathroom and
kitchen cabinets. At work, put strong latches on
cabinets where hazardous items are stored.
- Use screw-eyes or tongue-in-groove hangers to mount
mirrors or pictures instead of hanging them on nails.
- Be sure that ceiling fans and light fixtures are well
anchored or have earthquake safety wiring.
- Anchor typewriters, computers, televisions, stereos and
like items with heavy duty Velcro, at home and at work.
- Strap your water heater to anchor it to wall studs.
You can buy metal strapping, called plumber's tape or
strap iron, in hardware stores. Use it to strap the
heater at the top and bottom. This not only preserves
your best source of water but also significantly
reduces the fire hazard in your home by preventing a
broken gas line.
- Do not assume that anything is too heavy to move in an
earthquake. When the ground is going up and down in
waves, it bounces even the heaviest equipment into the
During an Earthquake
- Get under a heavy table or desk and hold on, or sit or stand
against an inside wall.
- Keep away from windows.
- If indoors, stay indoors.
- If outdoors, stay outdoors away from falling debris, trees
and power lines.
- If in a car, stay in the car.
- Many injuries occur when people act on their impulse to run.
Train yourself to take cover where you are.
Responses Inside Buildings During an Earthquake
For most of us the biggest danger in an earthquake is not from a
building collapsing, but from things inside the building falling
or flying around while the building is shaking.
Hazards found inside buildings include overhead lights, ceiling
tiles, cabinets, windows, furniture and equipment.
If an earthquake happens, the best thing to do is:
- Drop, cover, and hold on.
- Get under a table.
- If there are no tables, get under or down between rows
of chairs or against inner walls.
- Do not stand in a doorway. Buildings today have so much
partitioning, much of which is temporary, that many doorways
are actually weak points. Doorways are not a good solution
in a group situation either.
- If you have nothing to get under, sit down against an
interior wall or next to a chair, holding on if possible.
- If you are in bed, it's best to stay there, hold on, and
pull the pillows over your head for protection.
- If children are in another room, take cover in the closest
safe place and call to them to do the same.
Children will need you alive and unhurt after the
earthquake. Avoid the urge to run to protect your children,
as that puts you in more danger of being hurt or injured.
Responses if You are Outside During an Earthquake
- Outside, get away from buildings, walls, trees and power
- If you cannot get clear of hazards, getting back inside
a building is better than staying on the sidewalk.
- Sidewalks next to buildings are among the worst places
- In a car, ease off the accelerator and slow down carefully.
Do not stop on or under overpasses and bridges if you can
avoid them. Be aware of what traffic around you is doing
and act accordingly.
- If you live in coastal areas, be aware of possible tsunamis.
After an Earthquake
- Take basic precautions immediately after an earthquake. In
addition to those outlined in the General Family
Preparedness, Residential Fires and Hazardous Materials
Accidents sections you should:
- Expect aftershocks.
- Avoid using vehicles except in emergencies.
- Check yourself for injuries and protect yourself by putting
on shoes, work gloves and any other protective gear at hand.
- If the electricity is off, turn on a flashlight.
- Once you are sure that you're all right, check the people
around you for injuries.
- You might ask loudly, "Is everyone okay?" This will
also help calm people.
- The types of injuries that happen most often in an
earthquake include cuts, bruises, fractures and
- Check the entire building for structural damage and chemical
spills. Refer to the section on Hazardous Materials
Accidents for further response information.
Check chimneys for cracks and damage. The initial check
should be made from a distance. Have a professional inspect
the chimney for internal damage that could lead to fire.
- Right after an earthquake, hang up your phone. If the
receivers are shaken off the hooks, these lines register as
"open" in the system and it overloads. You can help restore
telephone service by hanging up your phone.
Special Considerations for Agricultural Producers
In addition to the precautions and responses covered in the
previous pages, the agricultural producer should consider the
- Immediately after an earthquake, animals will react with
great fear. Animals, including cats and dogs, that are
usually docile and accustomed to humans, may react
violently. They may bite, scratch or run at you.
- Earthquake aftershocks compound the problem of caring for
animals right after an earthquake. Aftershocks are quite
frequent after large earthquakes, and further increase the
fear and skittish reactions of animals.
- The best thing to do for animals after an earthquake is to
get them out in the open, to open pasture or rangeland. Let
the animals run free. Do not attempt to rope or chain large
animals such as cows and horses because they may injure or
kill themselves if an aftershock occurs and they try to run.
- Get animals out of barns or buildings that may have been
damaged in an earthquake. Barns are especially susceptible
to earthquake damage. Large beams and rafters may not be
well secured, thus making the barn subject to collapse
- Hay bales and large equipment may be tossed around and
come tumbling down on animals and people inside barns.
- Immediately open the doors and let the animals out.
It's easier to recover a live animal than replace a
- Ensure that mechanical equipment has not been turned over or
damaged. If there is danger of electrical shock, turn off
the main electrical circuit breaker or fuse. If you smell
gas or suspect a gas leak, turn off the main valve.
- Check fence lines and posts. You may need to build a make-shift
yard from temporary posts and fencing. Then
repair/rebuild the regular fencing, and open the temporary
yard when completed.
- If animal carcasses need to be disposed of refer to the
General Family Preparedness, Special Post-Disaster
Considerations section for appropriate handling.