Is a Tsunami Possible in South Puget Sound?

E

El and Bill

New member
Jim States asked me awhile ago, in the pub, about tsunami hazard in the South Puget Sound area. Yes, there is a significant hazard and there have been tsunamis there - significant ones in the past.

This is not an area where I have done geological research or earthquake hazard assessment, so I suggest the best information I could find is in the following document:

http://www.pmel.noaa.gov/pubs/PDF/gonz2526/gonz2526.pdf

In answer to a specific question Jim asked - there certainly are areas where landslides (submarine, terrestrial, or shoreline) have occurred in the South Puget Sound area, and there is evidence of land subsidence related to these liquefaction or slippage zones. Six to eight feet of vertical subsidence is easily possible. If a large quake occurred, particularly after long periods of rainfall and soil saturation, slippage along sloping areas would undoubtedly occur and much damage to structures built on these slip zones would result.

A geologist friend mapped the shallow geology of San Francisco, and it is his belief that the greatest structural damage in San Francisco when a big quake occurs will be to any structures built on these landslide areas. He mapped them carefully, and I hope that the planning commission there has used the USGS maps when considering construction of homes, other buildings, and highways.

I hope this helps answer your question, Jim.
 
I have a question. When boating how do you become aware that a tsunami warning has been issued?

What if you are at anchor - do you leave the radio on at all times? Are warnings broadcast on the weather channels? What about at night on the hook?

I know that when I am anchored or tied up to some tules in the delta, a lot of the time I have the radio off. When I sleep I always turn it off.

What do others do?

Steve
 
I dont worry about it that much. I listen to the radio a lot but you just cant do it all the time. besides if you are at anchor at night in a shallow ,50ft or less, bay and a tsunami hits chances are you are not going to live thru it any how so you might as well get some sleep. :moon
 
I am not so sure I agree with Tom on not living thru a tsunami if you are in 50 foot deep bay. A lot of the boats in Thiland survived the tsunami there. I suspect that the wave going out will wake you up--and with some luck you can fire up the engine, slip the anchor (leaving a fender on the end of the rode) and get out of the inlet. If you are in a normal fairly open bay, the tsunami may not be has high or cause as much damage. We were not far from a narrow inlet nearby had extensive damage--the area we were in had some strong surge, but no damage during a Sieche in the Med. A lot would depend on the depth of the water, the shape of the inlet and your reaction. I was amazed at how intact many of the boats in Japan were.

I would not leave my radio on--the chance of a tsunami is remote--probably less likely than being struck by lightning. An earthquake at sea feels like something just struck your boat--and was shaking it--so if that happens, get up, investigate and certainly at that point turn the radio on. Another option is one of the "weather radios" which only comes on if there is an alert. Hopefully you will have NOAA reception--but cruising the PNW there are lots of places where there is no reception.
 
I worked next to the analyst who ran the tsunami models for the west coast including Puget Sound (for 3 years) and threats to the south sound were minor. Landslides could have the most effect but think about the lack of deep water in the south sound and it makes sense. If you were at anchor, you would be relatively safe down here. It would be more dangerous at a dock because the effects are more pronounced at the shoreline and you have lots of objects to collide with. In the deeper waters of the north sound, the effects would be worse but nothing like they saw over in Japan with a direct coastal hit. Think about the presence of local faults, adjacent slopes with landslide potential, resulting wave angles, and depth of water to imagine your risk in protected waters. The open coast still involves angles and water depth but your source is far out of sight.
 
Bill
Thanks for the link and analysis of S Sound. Interesting reading. A few days a go I posted a link under earthquake prediction http://www.adn.com/2010/01/22/1107324/h ... -some.html - not a scholarly article. They implied that increased IR and perhaps other forms of electromagnetic currents could be detected by satellite a few days before. Their point was that seismology will only give us hx and location from which we can build statistical models. However the increased IR radiation or other forms of energy that might be detected from space may be another way of looking at that.

I am curious re: your opinion about the concept of great forces crushing rock, liberating detectable EMR. I wonder if that is similar to the thermocouple principle in our stove top fans, [two wires of different metals each end at different temperatures induces flow of current.

I know that before huge avalanches would occur in the Himalaya i could often feel a "snap" that was not really a noise but a sensation, sometimes many seconds or minutes before the avalanche would go down the face, just past our more protected ridge camp. Avalanche probably has some similarities to earthquake in that tremendous unreleased forces [potential energy] build up and then eventually release. During one white out, in the Canadian Selkirks in the Spring there were several wet slow moving concrete like avalanches all around us as we left a glacial cirque. I remember we could feel it coming before we heard it and then before we could see it.

Last point: I watched YouTube video few weeks ago about earthquake in alaska and that one of the three fishing boats in the area, actually survived almost a ground zero quake in a relatively narrow fiord. The wave carried them out over the land and back into the water. The moral - "it ain't over till you quit trying." so I agree w Bob - that quick action is better than doing nothing.

Jim

Thanks.
 
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