Geosciences. Japan Disaster: Tsunami

Transcription

1 All right. Thank you Ann, can you all hear me in the back? I don't need the thing? Thanks to Christina for putting this on, I think the idea was just to try to again, get some of the facts out, so we can move forward with a better scientific understanding of these events, and so my role is to talk about the tsunami, and in particular, I asked my, my 11-year-old what should I cover, you know, for this talk today, and she says, what do you do in the case of a tsunami. So, I'm going to slant it more towards that, and, and a few points following on the end of Ann's talk that was a good lead-in for where I'm going to go with this is, is kind of focusing on the event and doing the science, but also talking about what, how could this have happened to Japan, I think that was, to me, on the teaching side of it, one of the most shocking aspects, Japan is the most forward thinking nation in the world, with respect to national, natural disasters, and yet this happened there. And also, falling Christine's, Christina's comments, I'm not showing a lot of death pictures, so we'll talk about waves. 1

2 Just a general overview for the talk, I want to talk about what tsunami are, and I think because it's important for people to see this, put it in the context of historical tsunami, where does this latest event fit in, and, and where is it will change too, and continue to change over the next weeks, and I think from the geology standpoint, talk about tsunami forecast models. One thing about tsunami, nobody should ever die from a tsunami, period. They are very easy to model, they're easy to educate the public on if you can get the word out, and you have enough time, generally to get away, if there's somewhere to get away to. And, there's a reason why with the horrific amount of deaths from Japan, which, which was truly astronomical, it was still in order of -- still is an order of magnitude less than the Indonesian earthquake, I think because of advanced planning, on a similar style mega-thrust rupture. And so, again, coming into that then, what happened to Japan, finally ending for Ella on a, on a talk on, on tsunami preparedness. 2

3 So, tsunami, the definition is harbor wave, and it's a word I like because it connotates how tsunami energy, the wave itself, tends to get focused in small settings like harbors, and that's why the waves are so high, when they actually come ashore in, in certain enclosed spaces. They are always produced by some kind of underwater land movement, though not always by an earthquake, and for many of us that have a connection to the north state on the coast of humble, et cetera, Oregon, many tsunami occur from underwater landslides that are not necessarily triggered by, by earthquakes, and I think that's important to keep in mind. They are also called seismic sea waves, and tidal waves, I actually like the term tidal wave, but I'll come back to that, and another point, they can occur in any body of water that can get displaced. 3

4 And so, often I get asked about what was the biggest, or most deadliest, so here's, here's some of the, the factoids for that, the largest wave is shocking, 1,720 feet tall in 1958, and this was in an, in an embayment, and it actually was witnessed by people on the water in a boat, and, and it, it's phenomenal height, and so, it certainly could happen again. Of course, the most death was, was this shocking tsunami from 2004, notice it was in the Indian Ocean, I, grew up in California, and we often thought of tsunami as a Pacific Ocean event, but prior to the Indian Ocean, one of the largest and most devastating tsunami occurred in the Atlantic Ocean. And, other noteworthy tsunami are, are these, the, the large earthquake that Ann mentioned from Chile, in the 9.6, which has a segue way to, to Elizabeth's talk I wanted to mention that I was a student of Bob Dill, Bob Dill was a student of Francis Shepard, Shepard witnessed the 1946 tsunami from his rooftop in Hilo, and wrote a paper on it. 4

5 Major Tsunami by Death Toll , Indian Ocean Tsunami ,000 [1] 1908 Messina earthquake/tsunami , Lisbon earthquake/tsunami/fire 4. 36,000 Caused by 1883 eruption of Krakatoa Indonesia 5. 30, Hōei earthquake Tōkaidō/Nankaido 6. 27, Japanese earthquake 7. 25, Arica earthquake/tsunami 8. 22, Meiji Sanriku earthquake 9. 18, Tōhoku earthquake and tsunami , Mount Unzen eruption , Great Yaeyama Tsunami Based on Wikipedia list Here are these numbers, and it's an interesting list because it's hard to, in some cases, to, to decide which numbers come from the tsunami itself, versus after effects, obviously as we're watching unfold in the news in Japan, death toll continues to increase, I check one news report today that was so out of date in, in the manner of weeks, it talked about maybe 1,000 deaths, and, and it's hard to even gauge now what it is, and how it will continue to unfold, and so we see that for some of these numbers here too. Certainly one of the major ones was the Lisbon earthquake and tsunami that, that did significant damage to Portugal in

6 Okay. So, the main reason that we get tsunami is though, they're all from a shift of land below water, often due to faulting and falling up on, on Ann's talk, in California, at least in most of California, we're used to strike slip faulting, where the land moves this way, those can have large earthquakes, but they don't tend to displace water, it's the vertical motions are the ones that you have to concern yourselves with. And when the Japanese earthquake just happened, what was really shocking was the size wasn't -- was, was a major factor, the recognition, as we saw from the slides that Ann had that you were sitting on a deep sea trench, so we know that most of the faults are likely to have vertical motion, but that earthquake occurred 26 kilometers below the surface, which means there's a greater potential for the sea floor, itself, to move up, and so I'll come back to this towards the end, but just having a large earthquake isn't enough, the depth is, is important too, and the closer to the surface, the greater chance there is to have a large tsunami. As I mentioned, displacement due to landslides as well, volcanic eruptions, like Krakatoa, can lead to very large tsunami, and although it doesn't happen often, it has happened in earth's history that meteorite, or bowl-wide impacts can cause large tsunami. I put this picture in too, as just a side note to remind me that if you're going into the internet to steal images of tsunami from, from -- to put into talks, be very careful, the vast majority are fake, that I can tell, particularly the more outstanding they are, the giant wave, curling over a bridge, and the, you know, those, those are photo shopped in, this is from the Pmail web site, and at the end of the talk, I have a, a list of, of, of good web site resources for teachers, and, and others, and the Noah is an excellent source, and this is of the Sumatra tsunami. 6

7 Destruction of Tsunami Not a wave as much as a tide, hence tidal wave isn t such a bad term Water has a lot of weight and the force of a tsunami can be quite extreme Debris becomes a battering ram False sense of security because of length between waves I mentioned at the beginning that tsunami is a Japanese word that means harbor wave, and that they tell us in school not to say tidal wave, I think tidal wave is a great word, because it truly acts not like a wave breaking that a surfer would ride, but rather that the tide comes in incredibly rapidly, and for a long time, it's as if you had a super tide that then goes out and comes back in many times. And I link this to some Youtube sites, sites that I had loaded previously, but let's see... This actually is an interesting one, this was a film from Emeryville, down in the Bay Area, and this is the, the captured with a, you know, amateur, whatever that means, amateur camera from workers of the Japanese tsunami coming into the Bay, and it's slow moving, and it looks like a tide increasing, closer to the source, it will be faster moving, and, and larger as well, but this is sort of a good visual for the way these propagate. Yes, I saw that too. Oops it wasn't there before. All right. So, why are these waves so destructive? I, I think many of us have this false illusion of I'm a good swimmer, I surf, I can handle it. You can't, because again, it's not a wave that you can dive under, which is why it's damaging to have these fake images on the internet of a wave crashing, and you could hold your breath long enough, and pop up, and you've passed it, if the entire ocean raises 10, 15 meters, or even 5 meters, 15 feet, and rushes in, but it doesn't rush out again for half hour, or an hour, where are you going to go? And, it's more than water, and the water, itself, has, as I mentioned on the slide here, an amazing amount of weight and force behind it that can damage buildings, but more important is it works like a battering ram, cars float in, in you know, a foot of water, and so, when a, when a tsunami can come across, you're going to see lots of cars, and even houses floating along, as, as was seen in the image, and that's one of the real dangers of the tsunami, it becomes a battering ram. 7

8 Destruction of Tsunami Not a wave as much as a tide, hence tidal wave isn t such a bad term Water has a lot of weight and the force of a tsunami can be quite extreme Debris becomes a battering ram False sense of security because of length between waves Now, you have the force of the water, and also all of that debris in ships and buildings in front of it. And there's many images from Japan, this one I chose to show the, the battering ram aspect of it. And for this talk, what I want you to see is look at how much debris in just the very front of this, how are you going to swim through something like that, you know? And as more and more debris gets piled in, as well as dirt, it's, it's essentially a large battering ram, and as far as the tidal wave aspect, it's still coming in, and it's going to come in for a very long time. And then the last comment there is again, something that I know from teaching about tsunami s is that this is where a lot of destruction and deaths on the coastline, even from folks that know better, they see the water recede, the water comes in, they manage to survive by running up into a building, or tree, and then they come down to survey the damage, and then the next wave comes in, and often, the waves following the first are larger. 8

9 And, to demonstrate this I'll show where this data comes from farther on in the talk, but this is from a set buoys, and so these are open ocean waves, so even though it only shows an amplitude in the top of a half of a meter, a half a meter deep ocean wave, as you'll see, when it hits shore, can be quite huge, but my point of showing this slide now is this upper picture is from a buoy off of Kamchatka, and here you see the wave coming through, and a couple bumps, the red is the model that they expected the tsunami to travel, and then the black is the actual tide gauge information, and so there's not a lot of activity, but as it spreads out and widens, as it moves across the ocean basin, this is a, a buoy off of Oregon, look at the number of tsunami waves coming in, and notice the time in hours, you know, this, this covers a span of six hours of tsunami waves coming in and out, and so, an incredible false sense of security. The bottom line in, my earlier statement, tsunami can be predicted, and you can take cover, and so, you wait till the authorities say, okay, there's no more waves coming in, it's, it's a pretty simple way to protect yourself. 9

10 So, how are these tsunami measured? The way it works is there are, in the United States, and frankly for the world, the resources, the U.S. Geological Survey Earthquake Information Center in Golden, and that's where the seismograph information, seismographs to measure these earthquakes linked around the world, the information goes back there, if it's a large earthquake, it will get their attention, I mean, in a, in an electronic sense, and the type of fault, it gets calculated pretty quickly, and the depth, and if it looks like it has even a small potential to generate a tsunami, the information goes to the Pacific, the Hawaiian Pacific Tsunami Center, at least for the Pacific, although they're expanding around the world, and very quickly, they check to see if there actually has been displacement in the water, was a tsunami generated, sometimes they're not, even with large earthquakes. There was a pretty large earthquake this morning off of Japan in the same region, and initially, they issued a tsunami warning, and then when none of the gauges showed a tsunami, they canceled it. A, along the edge of the coast, they use tide gauges, again, still linked through the internet, so we have a central storehouse of information, and to issue warnings, and in the open ocean, there's a series of buoys called the DART System. 10

11 The way the DART System is actually pretty amazing, I find, the basics of it is the actual measuring device is sitting on the very bottom of the ocean in thousands of meters of water depth, and it feels the weight of all the water on top of it, and as a tsunami wave moves over the top, as it rises, you're getting that much more water, which is putting that much more pressure on the sensor, and so the sensor records the change, and the cartoon from Noah just shows the, the, the sensor sends information to a buoy that's floating, and that sends it to a, a satellite, which brings it back to the sensor. Holy smokes. 11

12 Okay. Here's this, a series of the buoys around the ocean basin, they're not that expensive to put in, if you consider how much damage causes, is caused by a tsunami, and so, after the Indonesian earthquake and tsunami, it was a wake up call to the world, a very sobering wake up call that we need to put more systems in other oceans, right now, it's still dominated by the Pacific. 12

13 Developing Prediction Models Tsunami waves propagate away from the source at a predictable speed This speed is affected by water depth The direction is affected by refraction and reflection If detailed maps of the ocean basin are available, one merely needs to plot the initial focus of the earthquake and energy parameters This can be accomplished very quickly and checked via the DART and local tide gauge data, further refining the model during an event Again, going back to this argument that tsunami waves are very easy to predict and model, it's very simple because there are waves that travel across an ocean basin, and the wave is easy to model for an open ocean basin, although the speed gets affected by the depth of the waters, as I'll show you, and also by waves bouncing and bending through refraction and reflection. 13

14 This just shows a simple equation for a tsunami wave in, in deep water, it has that square root sign, but look, there's only three variables, actually only one variable, the velocity is a function of the depth, the greater the ocean depth, the faster it's going to move. And, what we see in this upper picture is as that wave goes into shallower and shallower water, the friction on the wave causes it to slow down, which means the back part of the wave, and by the wave, notice this distance, wavelengths on the orders of hundreds of kilometers in the open ocean, as it gets, as that long wave hits shore, and it starts to slow down in the front end, the tail end is still moving fast, and all that water has to bunch up, and so you get a taller, and taller, and taller tsunami, that's why though, the dark buoys might measure a meter of displacement, you might get up to 10, 15 meters, and in the case of Japan, I'm still looking for the final numbers, but in places, it was recorded over 15 meters of the tsunami hitting shore. 14

15 Another aspect is refraction and reflection, so I just drew these quick cartoons. Imagine this is a basin. 15

16 An earthquake here sets off a tsunami, and you look at this boat. 16

17 The first thing the captain of the boat says is, well, we're protected by these islands that are going to get the brunt of the tsunami. 17

18 But waves bend around objects. 18

19 The waves are still bending in this cartoon. 19

20 And as it bends, the models have to take into account all this refraction, based on islands and shallow water depths, also reflection, where the waves hit, they're going to bounce back off at the same angle, my point of this very simple cartoon is it's somewhat complex things, waves slow down in shallow water, they bend around objects, and they bounce back 20

21 I'm going to jump through this real quick to say this, if you have good maps of the ocean basins available, you can make a model, and your model can, if you set up a tsunami in different areas, you can quickly model where the wave is going to hit at what time, and at what height, and based on that earlier slide I showed, we've seen in the last few years is the model is hitting the actual data after the tsunami dead on, and so we know that there are excellent ways to predict tsunami, even in very complex geography. The model is, that the U.S. uses is called MOST -- I know you're looking at your watch, I'll give you time though. 21

22 This is the MOST model, and actually it's narrated. Japanese tsunami propagating throughout the Pacific Ocean. As the tsunami radiates from Japan, it encounters complex topography within a period in the form of ridges, and volcanoes that create this complex wave pattern of scattering and reflective waves. On the eight hour mark, the tsunami had encountered a Hawaiian island, after nine and a half hours, it was hitting the West Coast of the United States. Notice how complex this wave pattern is becoming as it encounters more topography, and now you're seeing reflected and refracted waves throughout the entire Pacific. And at the sixteen hour mark, the tsunami now has propagated throughout the Pacific and is entering the Indian Ocean, and New Zealand islands. At twenty two hour mark, the tsunami had propagated throughout the entire Pacific Ocean, one way to simplify the interpretation of this complex wave deal is to compute the tsunami energy pattern, shown on this map. And the point I wanted you to take home from that is that was an incredible pattern, but when they actually got the data, it matched, and so, this is one thing we can, I think, trust the authorities on if you hear there's a warning. 22

23 What happened to Japan? Japan is the most proactive nation in the world with regard to natural disaster preparedness The tsunami was larger than anticipated and overtook barriers Far greater inundation than expected Collateral damage (e.g., landslides, fires) Difficult terrain So, what happened to Japan, here's the most proactive nation in the world with lots of experience, it was bigger than they anticipated, it breached the walls, in many places it was 30 to 45 feet high. It went farther inland than they had anticipated, and that's what caused a lot of the damage. And then, of course, like any natural disaster, there's the collateral damage, landslides occurred, fires, this was in an area of Japan of in some areas, a very steep terrain, and so they weren't able to get the emergency vehicles in time. 23

24 Tsunami Preparedness ALWAYS take warnings seriously! Sometimes the warning is merely the earthquake Recognize that tsunami are a series of waves that may encompass hours The first wave is not always the largest If you are on the beach and the water recedes, it will come back so seek higher ground And so, what can you do? Take the warning seriously, if you're on the coast and you hear about a warning going off, get away from the coast, don't, don't go to watch it, and don't think that you can just get up a little bit to watch it and you'll be protected. Know that tsunami, if you, the take home message, they are a series of tides going in and out, a sense of series of waves, and so you're not safe till somebody else tells you you're safe, it may encompass hours. The first wave isn't always the largest, and if nothing else, if you're in a part of the world that doesn't have a, a warning system in place, if you're ever at a beach, and the water recedes far more than it's been, get the hell out of the way, the water's going to have to come back, and this happened during the Indian Ocean tsunami, there were places where villages were saved by people who somehow knew that from some kind of education with no warning system, saw the water receding and rather than gather fish, went the other direction. Thank you. 24

25 Tsunami Resources on Web Pacific Tsunami Warning Center Resource for information. Official FEMA website. Another good resource from the University of Southern California. 25

26 YouTube Movie Sampler* uh1ujf4a Narrated Animation of Wave Model ture=fvwrel Amazing footage compilation ure=fvwrel Debris front of tsunami ure=related The tsunami at Emeryville Footage from Japan ture=related Additional Footage from Japan *As with all Internet content, please review for appropriateness. Most footage is not suitable for young children and comments are often off topic and inflammatory 26