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Tsunami

Coastal Tsunamis
A Tsunami is a large ocean wave caused by earthquakes and underwater landslides. These waves travel an average of 450 miles per hour in the open ocean. As they approach the coast, their speed decreases and their amplitude increases, reaching heights of over 100 feet. All tsunamis are potentially dangerous, even though they may not damage every coastline they strike. Damaging tsunamis are very rare.

Areas at greatest risk are generally 25 feet above sea level and within one mile of the shoreline. Most deaths are caused by drowning. Associated risks include flooding, contamination of drinking water, and fire from ruptured tanks and gas lines.

Inland Tsunami

Earthquakes or landslides can cause inland tsunamis. Land masses falling into the water can create a wave that would affect low-lying areas such as Dyes Inlet and Sinclair Inlet. Waves created by inland tsunamis can cause damage to ports, marinas and other structures or businesses on the waterfront.

Our coastlines are vulnerable but Westcoast tsunamis are infrequent. Understand the hazard and learn how to protect yourself. Be familiar with the tsunami warning signs.

Tsunami Warning Signs Are...
A strong earthquake lasting 20 seconds or more near the coast may generate a tsunami. A noticeable rise or fall in coastal waters could indicate a tsunami is approaching.

Warning Levels Are...


Advisory - an earthquake has occurred which might generate a tsunami
Watch - a tsunami was or may have been generated, but is at least two hours away
Warning - a tsunami was or may have been generated which could cause damage. People in the warned area are strongly advised to evacuate.

The West Coast/Alaska Tsunami Warning Center (WC/ATWC) is responsible for tsunami warnings for California, Oregon, Washington, British Columbia and Alaska.

The Pacific Tsunami Warning Center (PTWC) is responsible for providing warnings to international authorities, Hawaii and U. S. territories within the Pacific basin. The two Tsunami Warning Centers coordinate the information being disseminated.

For more information about the potential for a tsunami in the Puget Sound Area, please refer to the links provided in the Resource section to the right.