Quake and Tsunami hit northern Japan

[oldman]

Currents are not insignificant, when local bathymetry comes into play.
http://www.youtube.com/watch?v=1CDbsxf170Y

Took a look at that 'boo. Seems to me to be a rivermouth emptying, isn't it? Not like a beachbreak average Oz surfers bread and butter.

And another perspective:

http://www.youtube.com/watch?v=C8y2gL58 ... r_embedded

I give you the antichrist, her and her ilk are the number of the beast.

You must see this

Tohoku? That was some former earthquake?

Doesn't look right, the back on it is as big as the front. I'm suggesting possible fake, probably as one of those freak open ocean waves (stories of them scare the bejesus out of me).

Any details on that one Damage to check its authenticity? In open ocean at deep water a tsunami moves at incredible speeds and is (supposedly) experienced as an abrupt change in sea height/depth, i.e. no back on it, the water behind it isn't below the level of the front. :?

[oldman]

Ok the footage isn't the best but I would like to see someone try and paddle into this .... http://www.youtube.com/watch?v=YJRE6I-p ... re=related

This has been shown a bit since the event, but I suspect it can't be the leading edge of the tsunami. The photo of the same wave posted by someone else on page 4 clearly shows the beach already breached and the inland inundated, and the film shows this wave doesn't get past the beach and recedes.

Any takers on this, because I'm thinking it must have been one of the much later equalisation waves following the main event, and probably a fair bit later given that the period was measured in 70-80 minutes.

Just wondering.

[alakaboo]

This has been shown a bit since the event, but I suspect it can't be the leading edge of the tsunami.
Any takers on this, because I'm thinking it must have been one of the much later equalisation waves following the main event, and probably a fair bit later given that the period was measured in 70-80 minutes.
Just wondering.

No, it wasn't the first, it was the second round of waves. Not sure how long after the first round of waves.
I have Japanese tide gauge records of the tsunami, but I don't know where the footage was shot. If anyone can find out, and is interested, I can upload an image of the relevant tide records.
The period was only 70-80 minutes in deep water in the other direction, and only off Chile and Micronesia. I don't know exactly where the film was shot but the period of the waves in the north east of Japan was in the region of 20-30 minutes.

Tohoku? That was some former earthquake?
Any details on that one Damage to check its authenticity?

Tohoku is Japanese for north east. The earthquake is being called a whole range of things, the Tohoku quake, the Sendai quake (nearest big city), the Honshu quake (main island in Japan), Sanriku Oki quake.

The footage is legit, it was shot by the coast guard patrol vesell Matsushima which was 3 miles offshore of Soma in 38m of water. So the tsunami would have been slowing down and acting more like a wind wave, albeit much faster.

[Damage]

In open ocean at deep water a tsunami moves at incredible speeds and is (supposedly) experienced as an abrupt change in sea height/depth, i.e. no back on it, the water behind it isn't below the level of the front. :?

Hmmm not so sure about that olds. Isn't it just like a bigger version of the old rock-in-a-pond trick?

IE the world's biggest ripple aka sine wave?

[oldman]

Thanks for the responses gents.

As tragic as it all is, it is also fascinating, can't keep your eyes off it stuff.

Hmmm not so sure about that olds. Isn't it just like a bigger version of the old rock-in-a-pond trick?

IE the world's biggest ripple aka sine wave?

Don't know Damage. As 'boo points out, they can't model it, I think because there are too many factors (chaos?). One of the factors being how it is caused.

A meteorite, for example, would probably be more like a rock in a pond, but an undersea landslip would probably create a different effect (at least it does in my head). For example, if you have a flat board in a bath, and push it down suddenly, the wave effect is not a ripple but a surge. My understand is this is how it reacts in deep, open ocean water, which also explains how it moves so quickly.

Sure, scale makes extrapolation ridiculous, but it's the only way I can get my head around it, and explains how it is that a tsunami has no back to it.

The footage is legit, it was shot by the coast guard patrol vesell Matsushima which was 3 miles offshore of Soma in 38m of water. So the tsunami would have been slowing down and acting more like a wind wave, albeit much faster.

Thanks again. Interesting that it seems to be more like a wave as it approaches shore (3 miles and 38 metres depth would be akin to shoreline for a tusnami), and yet when it hits land it isn't, as shown by all the footage, especially that footage of it clearing the concrete embankments.

I suppose that can be explained by the fact that it must break like a conventional wave somewhere miles out to sea still, (now that would a f$#@%en sight) , and like a conventional wave, once broken it doesn't really have a back on it any more, i.e. more like a surge at that point.

Any other theories, observations? Happy to hear them.

[alakaboo]

Don't know Damage. As 'boo points out, they can't model it, I think because there are too many factors (chaos?). One of the factors being how it is caused.

They can't model it in shallow water when it starts to break, there are some very good models of the deep water propogation.
Still bloody complicated stuff:
http://www.youtube.com/watch?v=Lo5uH1UJF4A

Dangerous tsunami are only generated when there is a large vertical component of the movement.

This event was caused by a megathrust earthquake, essentially the Pacific plate is moving northwest and being subducted under the extension of the North American plate (which Japan sits on). The margin of the NA plate 'sticks' to the Pacific plate and is sucked down, then snaps up suddenly releasing enormous energy. These tend to be tsunamigenic.

For the Sydney region, the most credible cause of a large tsunami is a landslide off the contintal shelf. Which is a problem, because it may not be accompanied by any earthquake at all and there may be no warning. Even with warning, I think it is less than 15 minutes from shelf to shore.

Sure, scale makes extrapolation ridiculous, but it's the only way I can get my head around it, and explains how it is that a tsunami has no back to it.

Olds, where have you heard/read that a tsunami has no back to it?
This makes sense in shallow water (as the wave is spilling) but not in deep water where it is unbroken.

I guess you mean that because the wavelength could be up to 300kms, you don't see a peak and trough? In that case you'd be unlikely to notice the leading edge of the wave either.
In deep water (400m+), tsunamis are rarely more than 1.5-2m and wouldn't really do a lot to a ship. Due to the wavelength it would probably be imperceptible, unless you were very close to the origin.

Interesting that it seems to be more like a wave as it approaches shore (3 miles and 38 metres depth would be akin to shoreline for a tusnami), and yet when it hits land it isn't, as shown by all the footage, especially that footage of it clearing the concrete embankments.

I suppose that can be explained by the fact that it must break like a conventional wave somewhere miles out to sea still, (now that would a f$#@%en sight) , and like a conventional wave, once broken it doesn't really have a back on it any more, i.e. more like a surge at that point.

I meant more that it is starting to pile up on itself, rather than travelling as an unbroken ocean wave.
By the time it reaches shore it will have already broken and be spilling.
At that point you can think of them more like a very fast tidal surge, as you said.

[oldman]

Olds, where have you heard/read that a tsunami has no back to it?
This makes sense in shallow water (as the wave is spilling) but not in deep water where it is unbroken.

I guess you mean that because the wavelength could be up to 300kms

Yep, a 150km back is equivalent to none at all in appearance. I am talking about deep water. This also applies as it inundates the land, it is a tidal surge more than a wave at that point.

In deep water (400m+), tsunamis are rarely more than 1.5-2m and wouldn't really do a lot to a ship.

Usually measured in inches/centimetres or at biggest feet/10s of cms in open ocean, from what I have read, and usually not noticed in open ocean without sophisticated equipment. A 10cm pulse in open ocean with a 300km wavelength adds up to a very large wave when it hits shallows.

Tsunami very rarely break like normal waves, the change in water depth is just too dramatic for a wave of that wavelength.

Which is why that footage looked a bit suss. That looks very much like a normal, but abnormally large, wave. It would have been interesting to see it 'break', for want of a better term, but 'break' it must, at some point.

From what I have read, rapid change in water depth is what generates the Teahupo type wave. Longinus has explained in other threads that Teahupo is about at the limits of the physics for a wave to break like that, creating the inordinately thick lip and very shallow back.

Again, extrapolation is a limited tool to use in these sorts of dynamics.

Thanks for your attempts at my edumacation. I think we are saying the same thing.

But that footage!

[Damage]

Again, extrapolation is a limited tool to use in these sorts of dynamics.

Similitude > great word.

[oldman]

Similitude > great word.

Ha. Wikipedia'd it. Fantastic.

Loved this line.

"The design of marine vessels remains more of an art than a science in large part because dynamic similitude is especially difficult to attain for a vessel that is partially submerged: a ship is affected by wind forces in the air above it, by hydrodynamic forces within the water under it, and especially by wave motions at the interface between the water and the air. The scaling requirements for each of these phenomena differ, so models cannot replicate what happens to a full sized vessel nearly so well as can be done for an aircraft or submarine—each of which operates entirely within one medium."

Sounds like surfboard design!

[Damage]

Yep the principle of similitude allows you to study ocean liners et al in a laboratory wave pool. Or planes in an wind tunnel etc.

[mustkillmulloway]

Shallow feeble minded miserable sort of person aren't you mate .
only the lowest arsehole would attempt humor in the face of such a catastrophe.

farmers are always whinging how hard done by they are...for example i just saw a japenese farmer with three huge boats in his front yard and 25 cars in his back yard crying on tv his ruin

[Damage]

Ok Olds, allow me to take it one step further.

[oldman]

Ok Olds, allow me to take it one step further.

I'm more comfortable with philosophy and the search for truth than I am with engineering principles, but that stuff just leaves me tired and bored.

Philosophy, which used to be about the big questions, seems much more occupied with the very little questions that are the sub-sub-subsets of the few very big questions.

And consequently looks a lot like onanism.

[Damage]

Hey just sayin it's a great word. That's all.

[mustkillmulloway]

Shallow feeble minded miserable sort of person aren't you mate .
only the lowest arsehole would attempt humor in the face of such a catastrophe.

how about that poor nip who opened his cafe day the quake

got off too a shakey start

but the customers started floodin

got "glowing" reviews from workers at the nuke factory

[Roy_Stewart]

Ok Olds, allow me to take it one step further.

I'm more comfortable with philosophy and the search for truth than I am with engineering principles, but that stuff just leaves me tired and bored.

Philosophy, which used to be about the big questions, seems much more occupied with the very little questions that are the sub-sub-subsets of the few very big questions.

And consequently looks a lot like onanism.

I think that Popper's work is very important.

[Skipper]

I think that Popper's work is very important.

Come to think of it Roy, you strike more as a devote of his maverick student Feyerabend, who taught in NZ during the 70's.

[baddy]

Shallow feeble minded miserable sort of person aren't you mate .
only the lowest arsehole would attempt humor in the face of such a catastrophe.

farmers are always whinging how hard done by they are...for example i just saw a japenese farmer with three huge boats in his front yard and 25 cars in his back yard crying on tv his ruin

Shallow feeble minded miserable sort of person aren't you mate .
only the lowest arsehole would attempt humor in the face of such a catastrophe.

how about that poor nip who opened his cafe day the quake

got off too a shakey start

but the customers started floodin

got "glowing" reviews from workers at the nuke factory

spotted your bait poddy mullet fcuker
just proved my point
dipstick
at you fool