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Old 15-03-2011, 21:24   #1
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A Cascadia Tsunami - What to Do

There is a lot of informed speculation that a next major quake could occur on the Cascadia Fault: Cascadia subduction zone - Wikipedia, the free encyclopedia. This would mean an epicenter off the coast of Oregon, Washington, or British Columbia. I have been wondering what boats cruising the Salish Sea would experience in such an event.

Would you be best off to be out in the Strait of Juan de Fuca, or the Georgia Strait where you would be in open water with medium depths? Or would it be best to be up some of the craggy passages to harbours such as Prideaux Haven, Garden Bay, La Conner, or other similar harbours with many twists and turns between a rupturing fault and your boat?
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Old 15-03-2011, 21:42   #2
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Re: A Cascadia Tsunami - What to Do

Anywhere there is a land passage is not going to be a good spot to be in when the tide starts to rip. Mine's on the hard up a river and I'd still stay away if there's a tsunami.

Unless I were in the Strait close to sea I wouldn't bother. It's bad enough trying to get around Ft. Worden Park (Pt. Townsend).
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Old 16-03-2011, 19:57   #3
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Re: A Cascadia Tsunami - What to Do

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Originally Posted by St. Elsewhere View Post
There is a lot of informed speculation that a next major quake could occur on the Cascadia Fault: Cascadia subduction zone - Wikipedia, the free encyclopedia. This would mean an epicenter off the coast of Oregon, Washington, or British Columbia. I have been wondering what boats cruising the Salish Sea would experience in such an event.
Interesting thoughts. Officially, it's not a matter of if, but when, I was a kid when the 1964 quake sent a tsunami all the way down the coast. Our town at the end of a 30 mile inlet was basically destroyed. This length of inlet did give us some warning however, about 20 minutes. There were two waves, one 6' the other 15'. Many of the fish boats left the dock but had little time to get very far. Boats that hit the 60' depth mark seemed to fair better than those that didn't, rolling violently with some damage. Some made it to 100+ foot water and were bounced about a bit but survived with little or no damage. Freighter tied to the shipping dock were ripped from their moorings and beached.

After seeing the carnage at Santa Cruz CA (our marina had about a 1.5' rise but a lot of rip) after the latest Japanese event (a 4-6' wave) sinking about 16 boats and damaging many others, I feel it's better to get going as soon as you can. In the PNW there won't be a lot of time unless you're in you're boat already. If a large subduction quake hits near to shore (within 100 miles) you'll have about 20 minutes to get to high ground before the wave hits.

Best practice, set yourself up with the automatic alerts. If your on your boat head to deep water ASAP, lots of 400 + fathom water in the PNW where there will be little effect on your boat; you may not even feel it when it comes.
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Old 16-03-2011, 20:16   #4
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Re: A Cascadia Tsunami - What to Do

Must admit I was thinking about the same thing. If I was under way, I'd head for the deepest, most wide open water I could find and keep the pointy ends toward Juan de Fuca, while buttoning up as tight as I could. If there was to be a discernible wall of water coming, I think I would center the main, bring in the genoa about half way, turn on the engines and try and go as fast as I could in reverse until the wall hit. Tethered, of course.

If at anchor or tied up, I'd haul my butt up to the highest point of land possible and let the boat take care of herself.

Not a pleasant thought, but at least it gets something in our heads, "just in case."

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Old 16-03-2011, 20:20   #5
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Re: A Cascadia Tsunami - What to Do

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Anywhere there is a land passage is not going to be a good spot to be in when the tide starts to rip. Mine's on the hard up a river and I'd still stay away if there's a tsunami.

Unless I were in the Strait close to sea I wouldn't bother. It's bad enough trying to get around Ft. Worden Park (Pt. Townsend).
No kidding. The Pt Wilson rip can be bad enough on a normal ebb. Can you imagine it with a tsunami?

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Old 16-03-2011, 20:30   #6
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Re: A Cascadia Tsunami - What to Do

When a Cascadia earthquake causes a tsunami, I think there is time to only do one thing if you are anywhere near the danger zone:

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Old 16-03-2011, 21:02   #7
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Re: A Cascadia Tsunami - What to Do

When we were in the global tsunami in Phuket Thailand, the yachts that were anchored in more than fifty feet of water did fine. Yachts in shallow water did not fare as well, although the results were not predictable in all bays. Some bays did better than other presumably due to local bottom contours. The anchored yachts noted currents flowing past their yachts at a high rate of speed. We were outside Niharn bay at the time, and there was not a visible tsunami wave offshore, but the currents were amazing.

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Old 16-03-2011, 21:30   #8
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Re: A Cascadia Tsunami - What to Do

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Interesting thoughts. Officially, it's not a matter of if, but when, I was a kid when the 1964 quake sent a tsunami all the way down the coast. Our town at the end of a 30 mile inlet was basically destroyed. This length of inlet did give us some warning however, about 20 minutes. There were two waves, one 6' the other 15'. Many of the fish boats left the dock but had little time to get very far. Boats that hit the 60' depth mark seemed to fair better than those that didn't, rolling violently with some damage. Some made it to 100+ foot water and were bounced about a bit but survived with little or no damage. Freighter tied to the shipping dock were ripped from their moorings and beached..
Seahunter,

Thanks for the recollection of the great Alaskan quake. For those who were not here:
"The 1964 Alaska earthquake, also known as the Great Alaskan Earthquake, the Portage Earthquake and the Good Friday Earthquake, was a megathrust earthquake that began at 5:36 P.M. AST on Good Friday, March 27, 1964.[2] Across south-central Alaska, ground fissures, collapsing buildings, and tsunamis resulting from the temblor caused about 131 deaths.
Lasting nearly four minutes, it was the most powerful recorded earthquake in U.S. and North American history, and the second most powerful ever measured by seismograph.[3] It had a magnitude of 9.2, at the time making it the second largest earthquake in the recorded history of the world.[2][4]"
There was also the April 4, 1965, 6.5 quake that shook the lowlands of the Duamish Delta severly, but did not cause any tsunami.

Seahunter, can you please identify the harbor you are describing? It is interesting to know that a 9.2 quake at a great distance (maybe 1000 miles) has such significance compared to a closer medium sized quake. Much of it seems to relate to geology, as well as, magnitude.

The recent Japanese event only caused minimal results in the Salish Sea, minimal results at Kauai, but significant impacts at Hilo, Cresent City, and Santa Cruze. The shape of the bottom seems to play a large role in focussing the energy in certain areas.

I hope to gather information on the relative sensitivity of PNW locations to the megathrust events so that I can anchor or tie up elsewhere.

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Old 16-03-2011, 22:13   #9
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Re: A Cascadia Tsunami - What to Do

Growing up on the west coast of Vancouver Island was a blast in many ways. You didn't really have to go out in a boat to figure out how overpowering the ocean can really be. But once you get your feet wet, you never want to go back to land. In Canada, the Good Friday Earthquake (how it's known there) came at a time when there was little or no warning system available. Basically it was done by fishermen and tug boaters on radiophones.
Here's an interesting link:
On This Day - March 27, 1964 - CBC Archives

I'm not sure if anybody here has seen "Krakatoa East of Java" made in the late 60's (a mere few short years after the big quake in Alaska). There's a scene where the ship survives the tsunami after Krakatoa's dome collapses. I actually looked it up at the time and this part of the story was true. The captain tried to save his ship by throwing as much ground tackle off the front of his ship as he could. This kept the bow down and straight into the wave as they were overcome. He saved his ship and the passengers.
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Old 16-03-2011, 22:46   #10
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Re: A Cascadia Tsunami - What to Do

St. Elsewhere,
We in Hilo were not hit hard but Kona on the same island on the west side was. Homes were damage and boats were sunk. The Keehi Lagoon on Oahu got a lot of wave action which broke away piers and set many boats adrift.
There is another thread and you might search tsnami using the search engine after my signature.
kind regards,
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Old 16-03-2011, 22:47   #11
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Re: A Cascadia Tsunami - What to Do

Giant Megathrust Earthquakes
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