Friday, March 11, 2011

Tsunami

A number of people emailed today about the tsunami, including their concerns about radioactivity from Japan reaching the Northwest.

It turns out that the leading national research center for tsunamis is here in Seattle (National Center for Tsunami Research). At the Center they have developed numerical simulation models for tsunami events.

Here is a simulation of the unfolding of this event (click on it to enlarge):


You see how complicated the structure is? Multiple waves, reverberating off obstacles in the basin and refracting around islands.

Here is the maximum tsunami amplitude map there produced:

The largest amplitudes were near Japan of course, but significant amplitude propagated thousands of miles away. This predictions suggested northern CA would get hit harder than us and it was correct.

At Crescent City the observed maximum tsunami amplitude reached nearly 7 ft, while the NW coast only saw .5 to 1.5 feet. Impressive prediction.

Tsunamis...known as "harbor waves" is Japan...are produced when earthquakes cause a displacement of a water volume in the ocean. This generates waves that can move at tremendous speeds over deep water.... as a jet aircraft! Amazingly, the passage of a tsunami wave over the deep ocean is nearly imperceptible.

But bad things happen when the wave approaches a coastal zone. The propagation speed of the wave decreases when the water becomes more shallow and the water converges and rises, producing huge waves that can reach 30 feet or more.

Often the water level falls prior to the arrival of the tsunami wave, luring the curious on to the beach. Bad idea. If you see a sudden retreat of the water, RUN as fast as you can to higher ground.

Not only do we have truly excellent simulation models of tsunamis, but we have much better data on water height as well. Specifically, there has been an increase in the number of DART tsunami buoys. The number of DART buoys (see graphic below for map) was greatly increased after the Indonesian tsunami, with some of our local legislators (particularly Congressman Jay Inslee) playing an important role.

Here is the data from the Dart buoy near Hawaii. You can see the regularly varying tidal variations during the previous days, and the major changes during the last day due to the tsunami.


Regarding radioactive release in Japan, nothing to worry about. Even if there was a MASSIVE release there, it would be utterly diluted by the time it reached us.

9 comments:

izzit said...

Um... I hope you're right...
I see reports that fallout from past nuclear tests in China and the Pacific reached the U.S., and sheep in Wales are still radioactive 23+ years after Chernobyl:
http://www.guardian.co.uk/environment/2009/may/12/farmers-restricted-chernobyl-disaster
Could you discuss it at length? (Right now CNN seems to think the jet stream could reverse and blow the smoke back over Japan-!)

Kenna Wickman said...

It depends upon your definition of dilution is. There are areas in Europe where the amount of iodine released by Chernobyl was a concern, and remains so to this day. Also, I recall once when Seattle looked like Los Angeles due to dust that had blown in from China. Hopefully dilution would happen.

This earthquake serves as a reminder of what we can and will someday experience here. We have large subduction like earthquakes here every 300 years or so. Last one was in 1700. A good read is the book "The Orphan Tsunami of 1700" by Brian Atwater and others, UW Press. describes how they discovered this, and dated it to Jan 26, 1700 at 9PM, based on Japanese records,

KW

Urbancowgrrl said...

If folks here in the Pacific NW are worried about radioactivity, they have A LOT more to worry about from our own nuclear waste reservation in Hanford. So much radiation has leaked from that storage site that it is found in the Columbia and in local wildlife and affects crops and wild fish.

FreeRangeMom said...

Did we see any evidence of the Tsunami in Seattle-area Puget Sound?

bonobo said...

Great post, thanks

Kevin Purcell said...

Iodine-131 isn't the problem today in Europe. Its beta emitter with a half life of 8 days so within months it's decayed to undetectability.

I-131 is a prompt problem as it's gaseous (on initial release) and so is inhaled and preferentially deposited in the thyroid. When it is deposited especially on grass where dairy cattle graze (as it did at the Windscale fire in the UK) then it gets into the milk supply and is a problem for kids.

The current detectable isotope from Chernobyl in some locations in Europe is Cesium 137 with a 30 year half life.

BTW, I was at the University of Manchester on the day of the Chernobyl disaster. The nuclear structure physicists could see the Cs 137 depositing on their very sensitive detectors. It's not something you can keep secrete (as the USSR found out).

I'd also point out that Settle is a lot further from Fukashima than most of Europe is from Chernobyl.

And to add some meteorology all of these releases are tropospheric. Remember rain precipitates particulates out of the troposphere and in this case they will mostly be precipitated into the ocean. There wasn't a lot of rain about when Chernobyl was leaking.

The other issue was Chernobyl had no containment. The building was the only thing keeping the containment in. It is the only 7 class incident so far. Fukashima still has containment.

The irony of it all is Fukashima reactor 1 was to be retired om March 27.

Until we get more technical data from Fukashima it's difficult to say what is going on there. People don't distinguish venting slightly radioactive steam (with 5 second half life nitrogen that won't make it to the boundary of the site) from seeing more radioactive Xe or Kr (noble gasses so not much of a hazard for uptake) to seeing Cs, I, St, Ba, U, Pu and others which might indicate damage to the fuel system.

They also don't distinguish the amount of radioactivity released.

The most I've heard is that this is a 4/7 accident.

http://en.wikipedia.org/wiki/International_Nuclear_Event_Scale

Will Parker said...

Cliff, please keep updating the trajectory maps periodically over the next week. I promise not to make a radiation suit out of tinfoil or lock myself in the basement, but I am interested.

Also, the tsunami maximum-amplitude map seems to indicate that amplitude falls off rapidly when the waves encounter deep ocean trenches like those north of Australia & northeast of New Zealand. Is that a correct interpretation, and if so, what causes the damping effect?

Thanks!

peter said...

In the summer of 1962 I was a high school student working at the UW Laboratory of Radiation Biology processing biological samples from the Pacific nuclear test sites. On a whim (I think it as August), I took a geiger counter and some sample bags on a hike to Cascade Pass. I was startled to find radiation levels at some places exceeding 50mR/hr. Some moss samples I brought back to the lab measured > 10^5 DPM/g dry weight (mostly Cs137 & Sr90)...MUCH higher than the samples from the Pacific test site. Although the snow itself had fairly low activity levels, the melting winter snow pack (with resident radioisotopes) was filtered through and concentrated by plants and soil during the spring melt.
If we are going to detect anything from the Japanese reactor accident, we might wait until summer and go to Cascade Pass. The radiation levels I measured in 1962 were probably from big Russian atmospheric tests on Novaya Zemlya &/or Kazakhstan in the fall of 1961...a very dirty period of testing & a few months before the atmospheric test ban treaty.

Scott said...

For all the great work NOAA has done on tsunami research here, and for all the talk about the dangers of and potential for a Cascadia subduction zone quake, I have actually been able to find very little information about the potential effects, or how to plan for, a tsunami generated off the Washington coast. To the extent that I can find anything, it's all about communities on the coast. Products that deal with the Seattle area or Puget Sound are all oriented toward a quake on the Seattle fault. From what I read, that's both less likely and will generate smaller waves.

Maybe there is stuff out there I just haven't found, or can't understand, but if you have a chance, Cliff, can you link to anything talking about wave height forecasts and transit times within Puget Sound for a Cascadia quake? Or, if it doesn't exist, could you talk about why that might be, or if you know if anyone is working on it? It seems like a gaping hole in our local preparedness efforts, or maybe it just isn't something to worry about... I'd like to know which, though, if you happen to know!

Thanks!