Since 1812, the California coast has had 14 tsunamis with wave heights higher
three feet; six of these were destructive. The Channel Islands were hit by a big tsunami
in the early 1800s. The worst tsunami resulted from the 1964 Alaskan earthquake and
caused 12 deaths and at least $17 million in damages in northern California.
The 1992 Cape Mendocino earthquake produced a one foot tsunami that reached
Humboldt Bay about 20 minutes after the shaking. Although not damaging, this tsunami
demonstrated that locally generated tsunamis can reach our coastline quickly. Had the
earthquake lasted longer, the wave heights would have been higher. Evidence
suggests that large earthquakes capable of producing local tsunamis recur every two or
three hundred years.
WHAT IS A TSUNAMI (SOONAHMEE)?
A tsunami is a series of sea waves most commonly caused by an earthquake beneath
the sea floor. In the open ocean, tsunami waves travel at speeds of up to 600 miles per
hour. As the waves enter shallow water, they may rise rapidly. The waves can kill and
injure people and cause great property damage where they come ashore. The first
wave is often not the largest; successive waves may be spaced many minutes apart
and continue arriving for a number of hours.
LOCALLY GENERATED TSUNAMI
If a large earthquake displaces the sea floor near the coast, the first waves
the shore minutes after the ground stops shaking. There is no time for authorities to
issue a warning.
DISTANT SOURCE TSUNAMI
Tsunami waves may also be generated by very large earthquakes in the Pacific
These waves reach the California coast many hours after the earthquake. The Tsunami
Warning Center alerts local officials, who may order evacuation. Those in isolated
areas may not hear official evacuation announcements. A sudden drop or rise in sea
level may be a warning of impending danger. Move inland or to higher ground
WHERE AND WHEN DO TSUNAMIS OCCUR?
Tsunamis can occur at any time of day or night, under any and all weather
and in all seasons. Beaches open to the ocean, bay mouths or tidal flats, and the
shores of large coastal rivers are especially vulnerable to tsunamis.
WHAT IS A LOW-LYING AREA AND
HOW HIGH IS HIGH GROUND?
Typical peak wave heights from large tsunamis in the Pacific Ocean over the
years have been between 21 and 45 feet at the shoreline. A few waves, however, have
been higher locally- as much as 100 feet in a few isolated locations.
The best general advice available today is to:
Go to an area 100 feet above sea level, if possible, or go up to 2 miles inland.
you can not get this high or far, go as high and far as you can. Every foot inland or
upwards may make a difference.
Go on foot if at all possible because of traffic, damage to roads, downed
lines, and other earthquake debris.
HOW DO I KNOW
WHEN TO EVACUATE?
A major tsunami-producing earthquake will likely shake the ground strongly
for at least
20 seconds. Get into the habit of counting how long the earthquake shaking lasts. If you
count 20 seconds of strong ground shaking, evacuate as soon as it is safe to do so.
If evacuation is impossible, the third floor or higher of a reinforced concrete
may offer protection, but such a building should be used only as a last resort.
WHAT CAN I DO AHEAD OF TIME?
1.Make disaster plans now. Talk to the people you live with about what may
during a strong earthquake. If you live or work in a low-lying coastal area, know
where to go to survive a tsunami. Hold earthquake/tsunami drills at home or at
2.Assemble a portable disaster supply kit. Have a kit available in your car,
and at work. Your kit should include a portable radio with fresh batteries, water,
first aid supplies, flashlight, and extra clothes or a blanket. Put your kit in a
backpack and leave it in a convenient place.
3.Contact local emergency officials. Find out what areas are most vulnerable
tsunami hazards, which areas are safe, and which routes are best for evacuation.
4.Take a first aid class. Learn survival skills, talk with your family, friends
neighbors. Knowledge is your greatest defense against any potential disaster.
5.Join a neighborhood emergency response team. Contact your local Office of
Emergency Services to learn whether there is such a program in your city or
county. Or start one in your own neighborhood.