Video transcript
The video is 7 minutes and 32 seconds long.
Produced by the American Museum of Natural History, November 2005.
Visual: Tsunami footage from December 26, 2004
Speaker: Jody Bourgeois, University of Washington
When it first happened, I was so horrified that I didn't even want to be a tsunami scientist anymore.
Speaker: Man on the beach
Coming again! Bigger!
Visual: Tsunami footage from December 26, 2004
Speaker: Jody Bourgeois, University of Washington
It took me a couple of months to even begin to remove myself from the horror of the Sumatra event, and to begin to understand we would learn more science from that event, and that would help us avoid such death and destruction from future events.
Visual: Images of Washington coast, fisherman, waves
Title Graphic: Tsunami Science: Reducing the Risk
The most common and best-known cause for big tsunamis are cases where the sudden movement of the seafloor is generated during an earthquake.
Visual: Visualization of a subduction zone. Oceanic plate pushes down beneath the continental plate. Continental plate snaps up and pushes the water. Zoom up through the water into shot of tsunami waves moving across the water.
The biggest earthquakes on the planet happen along subduction zones, where the ocean floor is going down beneath the continent. When there is a sudden motion of the fault, it pushes the water and that's what generates the tsunami waves.
Speaker: Emile Okal, Northwestern University
Not all earthquakes create tsunamis in the same way. There is a certain element of guessing involved to make a judgment whether or not this earthquake will have generated a disastrous tsunami. And you have to do all of this in the few minutes or in the half-hour that you have, to issue a usable warning which could be passed on to populations and perhaps contribute to saving lives.
Visual: Montage of various tsunami models
There is a lot of research going on. For example, scientists known as modelers develop scenarios by running simulations of what this tsunami would be given a particular seismological scenario.
Speaker: Vasily Titov, Research Scientist, NOAA Tsunami Program
Visual: Vasily Titov in front of the tsunami model
What you have to do for the model, you have to, of course, you have to assume some sort of the earthquake source. That's the initial condition for the model.
Visual: Close up of the tsunami model
And the source that you see here is the source of the Sumatra event, which was about a thousand kilometers long here.
Visual: Vasily Titov in front of the tsunami model
So if you will it's the very first moment of the tsunami.
Visual: Full screen of the tsunami model
The red colors indicate the positive waves—the waves above normal sea level—and the dark blue are the troughs—the waves below normal sea level.
Visual: Vasily Titov pointing to the tsunami model
To the east, the initial wave was negative. It means that the water went down first before it went up. And that's what people saw in Thailand—the water withdrew from the coast first.
Visual: Beach in Thaliand showing the water before the December 26, 2004 tsunami.
That's the indication that the negative wave reached the coast first.
Visual: Vasily Titov in front of the tsunami model
So apparently, this simple model compared very well with all the data that we have about this tsunami.
Visual: Images of the the tsunami model
Our goal is to have the model of this type ready right when the earthquake happens so tsunami-warning centers can look at the model and have the ability to say when and how high the waves are going to be at the particular coastline.
Speaker: Emile Okal, Professor, Northwestern University
Visual: Map of North America. Zoom into the cascadia subduction zone. The state borders of Washington, Oregon and California appear on the map.
In the continental United States, in the lower 48, the region which is of primary concern for the generation of a local tsunami is the Cascadia subduction zone, which would include the states of Washington, Oregon, and the northern part of California.
Visual: Emile Okal on camera
We have never recorded instrumentally a large earthquake in that part of the world. The reason is that seismology is a very young science. We have had instruments only for one hundred years.
Visual: Research geologist, Brian Atwater carrying canoe down to Copalis River.
But we have several ways of assessing the seismic potential. One of them is geological fieldwork.
Speaker: Brian Atwater, Geologist, Unites States Geological Survey
Visual: Brian Atwater digging into river bank
I first came out here in the spring of 1986. At that point the very idea of very big earthquakes here was controversial, to say the least, among Earth scientists. Very few believed that they could happen here, and nobody had demonstrated that they had happened here. So our objective right now is to have a good look at a sand layer laid down right on top of a salt marsh that got dropped down deep into the tide zone here 305 years ago.
Visual: Brian Atwater in front of river bank
This salt marsh, represented by the soil here was way up at the level of the present salt marsh above us. The land abruptly dropped during an earthquake. The same down-drop happening here happened on the seafloor, and also other parts of the seafloor got raised.
Visual: Close up of sand layers in river bank.
Well, that made a tsunami, and that tsunami surged in here and laid out this sheet of sand.
Visual: Brian Atwater in front of river bank.
After that was all done, then the tides were free to come in because the land had dropped, so they laid down this mud, hence this three-layer cake of salt marsh peat, tsunami sand, and tide flat mud.
Visual: Brian Atwater canoeing down the river and digging into the river bank
The geological record of these great earthquakes goes back thousands of years. You can go out and see banks of tidal creeks like this one, that give you a 3,500-year history. You can see as many as eight earthquakes recorded in those banks. The average interval from one of these very big earthquakes here to the next is close to five centuries.
Visual: Brian Atwater on camera
We're three hundred years from our most recent one. But that doesn't mean you've got two hundred years necessarily to wait for the next one.
Speaker: Vasily Titov, Research Scientist, NOAA Tsunami Program
Visual: Bank of the Copalis River
Especially after the Sumatra event, we focus much more on the Cascadia subduction zone because the tectonic setting is so similar.
Visual: Footage of tsunami from December 26, 2004
We definitely don't want the Sumatra case to repeat itself. I'm hoping that we can get our system for the real-time warning done
Visual: Tsunami warning signs, images of people at the beach
so that next big tsunami that's going to happen will not catch us in a surprise like the Sumatra event did. And I'm hoping that the next big event anywhere, when it happens, we'll be much better prepared in terms of warning, in terms of mitigation, in terms of all the tsunami science.