Monster tsunami could devastate California: study (hypothetical 9.1 magnitude quake off Alaska)

A tsunami generated by a massive earthquake off Alaska could cause major damage to California's economy and force 750,000 people to evacuate, a report published Wednesday warned.

One third of all boats in California's marinas could be damaged or sunk, costing some $700 million in losses, while major ports would struggle to get huge cargo vessels out to sea in time to avoid being buffeted by tsunamis.

Experts from the US Geological Survey (USGS) based their damage assessment on the scenario of a 9.1 magnitude quake off Alaska's Pacific Coast, which it said was "hypothetical but plausible."

"In this scenario approximately 750,000 people would need to be evacuated, with 90,000 of those being tourists and visitors," said the report, co-published by the USGS and the California Geological Survey.

The number of tourists -- who would be more at risk because they may be less prepared for what to do -- would increase to millions in the event of a tsunami in summer months, when visitors flock to California's beaches.

"The good news is that three-quarters of California's coastline is cliffs, and thus immune to the harsher and more devastating impacts tsunamis could pose," said Lucy Jones, who led the study.

She also welcomed findings that neither of California's two nuclear power plants, both near the coast, would be risk under the scenario studied.

"The bad news is that the one-quarter at risk is some of the most economically valuable property in California," she added.

They are monitoring Mt. Rainier more and more, but still pretty limited. The towns and schools nearby it have lahar drills every so often, where the alarm goes off and they literally “run to the hills”. The closest school has 15 minutes IIRC to get to safety!

And the thing about these lahars, massive earthquakes, tsunamis, etc. - they WILL happen. And when they do, it will be a huge mess. A large quake on the Seattle fault (discovered 30 years ago?) would devastate Seattle (including a tsunami in Puget Sound and/or Lake Washington!), and would turn it into an island full of rubble. (With the lakes and rivers - it is only accessible by bridge, which most would be knocked down if a huge one occurred).

I was talking with one emergency responder, and he said that for a large Cascadia quake (subduction zone fault out in the ocean), the plan is to fly supplies into Moses Lake (large runway for airplane testing), truck two hours to Cle Elum (just east of the mountains), then chopper it into Seattle and suburbs. (The bridges on the west side of the mountains would be destroyed.)

The 3-day emergency plan is a joke, but they are stressing a 7-day plan. I’m guessing that it will be weeks and weeks of REAL hardship WHEN “the big one” happens.

The large Cascadia fault off the coast of Washington last went in 1700 AD, the huge tsunami hit the coast in 15-20 minutes, and has ruptured at 200 to 1000 year intervals, with an average period of events of about 500 years.

Ok. I did my final paper for my BS on Alviso - just saying.

I lived on the water in the Bay for ten years. The Bay is not "flat;" the water slopes as the tide moves in and out. I knew the tides and how much comes in the Gate, and what the differences are in the tides as a function of time. Alviso would be at minor risk to a "tsunami" during a rainstorm at high tide. There is little to no way it would be at risk from a tsunami at low tide below "mean lower low water" (the definition of "sea level" for purposes of charting). The tides in the South Bay can be two and a half hours later than at the Gate and about 6" different in height at that point. Needless to say, the peaks are less of a difference than at maximum flow when those differences exceed a foot. If a tsunami hits when the gravitational tide is outgoing, it would take almost three hours for it to disperse over the San Francisco Bay as far as Alviso. The reason is that the height of a tidal wave at sea is almost unnoticeable. The only reason it gathers in height is when the wave base strikes land, just like a regular beach wave. The pulse of water in a tidal wave is too short in duration to supply sufficient water to raise the Bay level by more than a foot by the time you get that far from the Gate. Therefore, chances are Alviso would be unharmed - just saying.

As to Alviso as a port, the reason it was uneconomic even for bulk goods was the cost of labor. One had to load and unload the boat and then load and unload another mode of transportation to get the goods to or from another location. Rail put those goods closer to town centers and they were dominant for that reason. By 1879 there was even a train to Los Gatos. Needless to say, the water coming into Alviso is also very shallow, making it a challenge for the few specialized barge-tug systems to navigate without running aground. When the tide went out, they had to wait. That put a limit on traffic. There were losses from loads running aground and costs of maintenance for barges that twist and bow under load if they have to sit on the bottom. The reason I know that is because I restored antique boats during that ten years of living on the Bay (including George Shima, the wheelhouse of which is now in the San Francisco Maritime Museum, which was a tug named after the owner that ran potato barges up to the Delta, also shallow water).

BTW, the reason I put "tsunami" in quotes is that our wondrous academics decided for us the unwashed that the term "tidal wave" was inaccurate in describing a seismic wave and therefore adopted the Japanese term for a seismically induced wave. Little did they know that the term "tsunami" translates directly to "tidal wave."

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