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Tsunami FAQ PDF

Q: Is San Juan County at risk for a tsunami?

A: The short answer is yes. Tsunamis are rare, and there is little historical information as to their extent or severity. Recently scientists have begun using high-powered computers to model various seismic events and the resulting tsunamis. The current thinking is that in the event of a large earthquake (magnitude 9.0) on the subduction zone located off of the outer Washington coast, San Juan County could expect a tsunami anywhere from 90 to 180 minutes later. Tsunamis are drastically affected by bathymetry, topography, and geography- but a best guess says that the waters will reach a height of 10 feet above mean high tide in most places, and potentially a height of 20 - 30 feet at the head of long inlets. In most cases a tsunami is not so much a breaking wave, but rather a sudden and fast moving increase in the tidal level (hence the name tidal wave). Picture the tide coming in over the course of minutes not hours.

Q: How do I know if I’m living in a high-risk tsunami zone?

A: There are numerous high-risk tsunami areas within San Juan County. Click HERE for photographs of areas within the County that are potentially at risk; these pictures are meant as examples, not as a comprehensive inventory. The closer you are to the high tide line, the higher the risk. Areas at the head of narrow, deep inlets are more at risk than areas along the outer shore. Places where water is funneled will see an increase in both the height and force of the wave. For more help with understanding the risk in your neighborhood, feel free to contact DEM directly.

Q: How dangerous is a tsunami?

A: In the most likely scenario, San Juan County will have plenty of warning before a tsunami in the form of an extremely large earthquake. This gives us an hour or so to pack up families, pets, and valuables and head away from the shore. The danger from tsunamis comes from rapidly rising water, as well as fast moving debris entrapped in the flow (cars, boats, docks, driftwood logs, and other items become potentially devastating battering rams). It is important that once you leave, you stay high until you are sure that the threat has passed (after a large earthquake, repeated tsunamis are possible over the span of up to 24 hours). Tune in to your local media or your EAS radio for updates.

Q: What can I do to protect against tsunami damage?

A: The highest priority is to protect yourself and your family. After an earthquake large enough to knock you off of your feet, act as though a tsunami is coming and move to higher ground. Equip yourself with an EAS radio in order to hear tsunami warnings. To mitigate damage to your home, the first thing to do is to think twice before building right on the beach. Ensure that the pilings of any floating dock in front of your house extend 12 feet above mean high tide, enabling the piers to float up with the level of the tsunami and avoiding the release of boats and docks as debris. A tsunami is a relatively rare but massive event; the priority is always to protect lives over property.

Q: Is this info available in a flyer or handout?

A: Yes, click here to link to a short informational flyer on tsunamis in San Juan County.

Q: Where can I learn more?

A:Visit the web site of the West Coast & Alaska Tsunami Warning Center.