Tsunami and Seiches

Tsunami are very rare events in Seattle, in fact there has not been a tsunami here in recorded history. Despite their infrequency, they have been included here for two reasons: our geology tells us they have occurred here and modeling predicts the consequences would be severe.

Seiches are the lesser known cousins of tsunami. They are another type of long period wave that gets created when enclosed bodies of water get pushed and pulled. The effect is very similar to creating waves in a children's pool by rocking the edge back and forth. Seiches have been more common here than tsunami, but have been far less destructive than a potential tsunami.

Major Incidents

Issues to Note

Tsunami are often triggered by a strong earthquake, but landslides can cause them, too. Such slide generated tsunami have occurred in the Tacoma Narrows after the 1965 earthquake and in the Columbia River.

Tsunami generated in the Pacific Ocean are a major threat to the Washington coast, but not to the inland waters. The waves would get reflected back to sea, diffused and lose speed as they entered Puget Sound.

A tsunami generated by the Seattle Fault would inundate major parts of Seattle ringing Elliott Bay. It would strike minutes after an earthquake that would be devastating in its own right. The best method of escape would be vertical evacuation - getting inside a building and getting to the highest floor possible.

On the Web

How to Prepare for Tsunami (pdf). Information from the City of Seattle, King County and Washington State.

Animation of Seattle Fault Tsunami. National Oceanic and Atmospheric Administration (18.6 MB, Quicktime).

NOAA Center for Tsunami Research.

Tsunami Hazard Map. Poster sized pdf from the Washington State Department of Natural Resources.

NOAA Time Seattle Tsunami Mapping Project. Technical report from the National Oceanic and Atmospheric Administration.

Tsunami Safety Facts from Windows to the Universe (University of Michigan).

Seiche Model from Earthguide (from Scripps Institution of Oceanography).

Audible Warning System Q & A. This system is deployed on the Seattle waterfront to warn of hazards like tsunami.