What does the West Coast & Alaska Tsunami Warning Center do?

¨     The main purpose of the WC/ATWC is to provide tsunami warnings for Alaska, Washington, Oregon, and California in the USA and British Columbia in Canada for any tsunami source in the Pacific region that could be dangerous to these areas.

¨     Community Preparedness: Staff provides information to people in coastal areas to educate against the threat of a tsunami.

¨     Applied R&D to improve the center. We are continually improving techniques, improving response times, and improving communications to people in affected areas.

¨     This service is provided by six people, 24/7/365. Two people are always on duty.

When is a warning issued?

¨     In our Area of Responsibility (AOR), a warning is issued to coastal areas for any coastal earthquake that has a magnitude of 7.1 or greater. The warning area surrounds the earthquake source. This means residents in warned areas must evacuate.

¨     The warning is issued within 15 minutes after an earthquake occurs.

If you feel a large earthquake, should you wait for a warning or evacuate?

¨     A general rule-of-thumb is, if hard shaking takes place for 15-20 seconds, you should evacuate.

¨     If you are in a coastal area and if you are frightened due to the intense shaking, you should evacuate.

¨     The closer you are to the tsunami source, the less time you have to get away!

How are tsunamis generated?

¨     Tsunamis are generated by vertical crustal movement of the sea floor. If the sea floor movement is horizontal, a tsunami would not be generated.

¨     Tsunamis are also caused by landslides into or under the water. These landslides are often triggered by earthquakes and the generated tsunami often occurs within minutes after the shaking stops.

¨     They can also be generated by volcanoes and large meteorites.

Do all large earthquakes, greater than magnitude 7.0 generate dangerous tsunamis?

¨     NO. Only those with large amounts of vertical sea floor displacement. We could have a large coastal earthquake with horizontal motion. However, exact seafloor displacement is not known at the time the warning is issued, and we cannot take a chance with peoples’ lives – therefore evacuation must take place.

What was the biggest earthquake ever recorded?

¨     The biggest earthquake occurred in Chile (9.5) in 1960.

¨     The second largest was the Alaskan earthquake (9.2) of 1964.

Does Alaska have a history as a dangerous tsunami source region?

¨     In the past 20 years, 10 tsunami warnings have been issued by the WCATWC.

¨     In the last century, three of the 10 largest earthquakes in the world occurred in Alaska (1957, 1964, and 1965).

¨     In recent history, four of Alaska’s earthquakes (1946, 1957, 1958 and 1964) generated tsunamis causing death and destruction throughout the Pacific.

¨     1946: over 100 feet on Unimak Island.

¨     1958: about 1700 feet at Lituya Bay.

¨     1964: over 200 feet at Shoup Bay, upper Prince William Sound.

After a warning is issued, who evacuates people and how can I prepare myself?

¨     We issue warnings to State Emergency Officials and they evacuate people.

¨     You should know where to evacuate. Most coastal communities have an evacuation plan and safe areas. This information can be obtained from your local emergency official.

¨     You should know what to do before an earthquake, during an earthquake and after an earthquake. This information can be obtained from State and local emergency officials, Red Cross, or the WCATWC.

How fast do the waves of a tsunami travel and can you see them in the open ocean?

¨     In the open ocean they can travel over 500 miles/hour (water depth > 17000ft). In shallow water, say 60ft, they travel about 30 miles/hour. You cannot outrun them with a boat.

¨     For example, a tsunami would travel from Sand Point, AK to Hawaii in about 4.5 hours and to California in about 6 hours.

¨     You cannot see the wave in open ocean where they will likely be less than 3 feet high.

Does the West Coast and Alaska Tsunami Warning Center have a web page?

¨     Yes! It is http://wcatwc.arh.noaa.gov.

¨     The URL contains our most recent released messages, plus other useful information.

Are you open to the public?

¨     We are open to the public every Friday from 1-3pm so that they can learn about tsunamis, earthquakes and how we do what we do.

Can you predict earthquakes and tsunamis?

¨     No, we cannot predict earthquakes.

¨     At this time we cannot predict whether a large coastal earthquake will generate a tsunami.

¨     Tsunami wave heights can not be accurately predicted near the earthquake source. Away from the source, tsunami wave heights can be estimated.

¨     Tsunami arrival times can be estimated.

Can Anchorage, AK have a tsunami?

¨     Not likely due to its location with the Cook Inlet, which is relatively shallow.

What does the word “tsunami” mean?

¨     Tsunami (soo-NAH-mee) is a Japanese word meaning wave in a harbor.

¨      It is a series of water waves of extremely long wave length and long period.

How does the WCATWC determine when an earthquake happens; if a tsunami is generated, and alert emergency officials and others?

¨     Seismic Data: We use seismometers which record earthquake shaking. These instruments are in Alaska, the lower 48, and throughout the Pacific basin. This data is transmitted to our computers in Palmer, AK.

¨     Water Level Data: We determine if a tsunami has been generated by checking tide gages and tsunami detectors which are located in coastal areas and throughout the Pacific basin. We can then see if a tsunami has been generated.

¨     The information is disseminated to emergency officials, media, and the public by special communications lines, satellite, internet and telephones.

Can a tsunami sink a ship?

¨     If that ship is near the shore, a large tsunami could destroy the ship or move it inland. This is why ships should to move to deep water.

¨     In the deep ocean water a tsunami could pass and a ship may not know it.

¨     A tsunami can become very large as it nears a coast line. This depends upon the initial tsunami generated at the source, and the impact region (shape of the harbor, its bathymetry (depth), topography, etc.).

Has the US West Coast experienced any damaging tsunamis?

¨     Yes! In 1812, 1927, 1960 and 1964. For more detail see the web link http://wcatwc.arh.noaa.gov/web_tsus/pastaor_tsunamis.htm