Sumatra earthquake.

[Soapy Sam]

I'm surprised there's been no comment on the Sumatra earthquake. Or have I missed it?

 

[Rolfe]

I'm surprised there's been no comment on the Sumatra earthquake. Or have I missed it?

I've seen nothing, though maybe I should look again in the General Scepticism forum for the obligatory "where were the psychics when they could have made a real difference?" thread. Edited to add, I see the thread has actually been started.

Also, I suppose where was the organised warning system which with hindsight would have been a real smart wheeze.

Finally, what happened 40 years ago? They say this is the worst earthquake for 40 years, but nobody's saying what happened then.

Soapy - you weren't near the trouble zone, were you?

Rolfe.

 

[fishbob]

40 years ago was the 1964 earthquake in Prince William Sound, Alaska. 9.2 or 9.3. There were large tsunami waves in the Sound and in Resurrection Bay, but I don't recall if any made it out across the Pacific.

 

[fishbob]

USGS Earthquake Activity site

 

[Soapy Sam]

Rolfe- Do I detect a trace of concern?

Nowhere remotely near.

A retired couple I know from Wishaw were in Thailand. My mother has heard nothing of them. A couple of guys here are from various parts of the pacific rim. They report a lot of unanswered telephone lines. We can't get them off the rig because freezing fog has our choppers grounded.

Hell of a thing.

 

[patnray]

Re: Re: Sumatra earthquake.

Also, I suppose where was the organised warning system which with hindsight would have been a real smart wheeze

Rolfe.

There was an article about tsunami warning systems some time ago in Scientific American. The basic problem is they are long wavelength low amplitude waves as they travel across the open ocean and are thus hard to detect. Only when they approach a coast and the water depth is less than some fraction of the wavelength do they pile up into tall destructive waves. Nevertheless there are bouy systems which can detect them amongst all the other waves and noise on the ocean surface and provide some warning for parts of the US (and Japan IIRC) that are deemed at risk based on past events. Unfortunately there were none in this part of the world...

 

[AK-Dave]

The big problem with a warning system is who pays for it in the local communities. The detection and prediction of tsunamis is relatively easy. Both the Alaska and Pacific Tsunami Warning Centers determined a tsunami was going to be generated, but they had no one to call and warn. Even if they could have gotten the warning out to local governments, those governments did not have a warning infrastructure in place to disseminate the warning. Without organized evacuation plans and routes, even with a warning system there still would have been great loss of life. In my line of work, tsunamis are the threat we take most seriously, since it is pretty much the only disaster where you can save lives after it happens by getting people evacuated before the wave gets to them. One downside to tsunami detection and warning is that they can tell based on location, magnitude and depth if a tsunami will probably occur, but they can't predict how big it will be until it starts impacting the shoreline somewhere. This leads to tsunami warnings being issued and cancelled on a regular basis and the possibility of people ignoring them.

See this article on the Alaska Tsunami Warning Center regarding this earthquake.

 

[AK-Dave]

Here is an animation of the tsunami propagation:

 

[Rolfe]

Regarding early warnings, BBC News 24 reported that the Pacific system in Hawaii picked up the Indian Ocean quake about an hour after it happened. They knew it was no danger to their area, but recognised the danger to south east Asia. It was probably too late already for Sumatra and Andalan, but they could have warned Sri Lanka, except they had no contact numbers and no system to get information through.

I still wonder how come nobody managed to warn east Africa.

So far as paying goes, who's going to pay to clear this up? Be a lot cheaper to pony up for a warning system methinks. Except I hear the ringing neigh of a bolting horse listening to idle talk of bolting stable doors.

Soapy, I still think there are far more people simply incommunicado than actual casualties. The odds are favourable.

Rolfe.

 

[varwoche]

40 years ago was the 1964 earthquake in Prince William Sound, Alaska. 9.2 or 9.3. There were large tsunami waves in the Sound and in Resurrection Bay, but I don't recall if any made it out across the Pacific.

Not sure about across the pacific, but people died in Oregon and California.

 

[Chris Haynes]

40 years ago was the 1964 earthquake in Prince William Sound, Alaska. 9.2 or 9.3. There were large tsunami waves in the Sound and in Resurrection Bay, but I don't recall if any made it out across the Pacific.

In my 8th grade Earth Sciences class we saw some incredible movies of the effect of that tsunami. It included some film that was recovered afterwards... it was taken from a ship that was docked showing kids on the dock waving to the people on board --- and then they were gone.

We were living in Ft. Ord, CA in1964... and I remember that all the beaches were closed and I heard that there was quite a bit surge up the creeks and rivers (I was in 2nd grade).

There is an article about that tsunamini on the West Coast & Alaska Tsunami Warning Center website:
http://www.wcatwc.gov/64quake.htm

editted to clarify a time

 

[Art Vandelay]

Regarding early warnings, BBC News 24 reported that the Pacific system in Hawaii picked up the Indian Ocean quake about an hour after it happened.

So the earth waves traveled several times as fast as the ocean waves?

Is a tsunami a single pulse, or is a sustained wave? What are the amplitude and wavelength in the open ocean? Does a tsunami travel at the speed of sound in water? How well do they turn corners? Do they bounce off of coastlines? How much of a lee did Sri Lanka make on India? Was there interference there, with some places having destructive interference, and some having constructive?

 

[Badly Shaved Monkey]

Has any one found a good description of the facts and figures for this tsunami: how tall were the waves in various places, how far inland did they penetrate, is there a map showing the areas inundated? How did anyone survive on those chains of islands that are only a metre or two above sea level at maximum?

There is a lot of damage at the coastal fringes and in some of these countries the interior is mountainous and/or forested with few roads, but why, in contiguously inhabited and populous places like Sri Lanka, can't people just walk, or be shepherded, inland to towns and villages with intact water supplies and food stores? When we have floods in this country (UK) it is an irritating habit of news reporters to stand knee-deep in water in a flooded street telling us how dreadful it is, but the helicopter shots show that only one street is flooded and if the ground level camera was pointed in another direction you'd get a whole different view of the scale of the problem. The Indian Ocean rim disaster is on a vastly worse scale but I have found myself singularly lacking a clear picture of the real physical scale of the problem.

 

[HarryKeogh]

Has any one found a good description of the facts and figures for this tsunami: how tall were the waves in various places, how far inland did they penetrate, is there a map showing the areas inundated? How did anyone survive on those chains of islands that are only a metre or two above sea level at maximum?

I second the call for this information. Aside from the terribly vast (and heart-wrenching) number of dead I have trouble picturing the scale of this thing. Did the water reach a few hundred feet inland? a 1/2 mile? a mile? I haven't a clue and the news articles that I've read haven't mentioned it.

 

[Correa Neto]

If you are asking for an average figure of how much the water went inland, this is something hard to tell (and perhaps statistic figure not much worthy of trust). A number of factors are related to this, those that came to my mind are, besides the location in respect to the earthquake epicenter:

(i) continental shelf slope and width- gentle slope angles along broad and wide areas can help dissipating part of the energy;
(ii) shore configurations- underwater structures such as such as sand strings, reefs, etc. would act as barriers, again dissipating the energy;
(iii) configuration of the shore area above the water, steep sorelines would allow smaller inland water penetration.

Sure, there are a lot of other constraints, such as some coast geometries could focus the waves, etc.

Each particular configuration would result in a given effect, hipotheiticaly resulting in something like at A the sea went 200 meters beyond average shoreline while at B, 1 km to the east, it entered 2 km.

As for people walking away from the disaster, well, from the (sparse) knoweledge I have of the area, I assume that at least some affected areas are surrounded by mangroves, swamps, muddy flats, etc. Not exactly easy paths. Besides, many people will not want to leave for a number of reasons (search for missing relatives and friends, help neighbours and relatives, try to fend off looters, see what can be salvaged of their possetions, etc.).

Art Vandelay:
Yes, seismic waves travel faster than tsunamis. The denser and more cohesive the medium, the faster they will travel. And usually tsunamis are generated by the earth movments that follow earthquakes. Something like this (please note that this is VERY simplified):

A fault (a plane that separates two rock blocks moving relative one to the other) is locked, what means that the blocks can´t move. Stress builds up, and then it obstacle gives away and all the stored energy is suddenly released as shock waves and a sudden movment of the rock blocks. Now, the surface will go up and down, oscillating according to the passage of the shock waves and at some places, some movment will also happens due to the movment of the blocks. Water is dislocated due to these movments, creating tsunamis.

 

[Chris Haynes]

Today there are comparison sattelite photos at www.washingtonpost.com (registration may be required). They show before and after, and much of the devistation.

Also... I read that there had been a panic in India because the officials there got a warning of another earthquake from US officials. It seemed odd that seismologists would do something so irresponsible --- and as it turned out, they got the info from a charlaton:
http://seattlepi.nwsource.com/local/206020_warning31.html

This guy has no remorse for the hardship and panic he caused... and does not understand why real scientists are not buying his ideas --- while he sells his book on earthquakes for over $100 !!!

 

[jj]

So the earth waves traveled several times as fast as the ocean waves?

I don't have the numbers at hand, but it's in the "much faster" range.

Is a tsunami a single pulse, or is a sustained wave?

I understand what you're asking, but I guess the answer is "something else" because it's a nonlinear process, and so doesn't have a nice "wave" analysis reduction in many ways.

Because of the way the wave propagates, the speed, amplitude and wavelength are all coupled in nonlinear ways.

What are the amplitude and wavelength in the open ocean?

Ugh. Something I used to know the answer to.

Does a tsunami travel at the speed of sound in water?

No. Sound in water is a compression wave. A tsunami is not a compression wave, although it has some facets thare are, perhaps, barely like one. It propagates slower than a sound wave in water.

How well do they turn corners? Do they bounce off of coastlines? How much of a lee did Sri Lanka make on India? Was there interference there, with some places having destructive interference, and some having constructive?

Hmm. That's not a 1-paragraph answer. Maybe somebody fresher than I on the subject will say something. Sorry.