PubTalk 2/2014 — 1964 Great Alaska Earthquake and Tsunami 50th Anniv.

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By George Plafker, USGS Geologist Emeritus

 

  • March 27th, 1964, one of the most violent earthquakes of all time rocked southern Alaska.
  • More than 50,000 square miles of the state was tilted to new elevation, and the resulting property damage disrupted the state's economy.
  • Within 24 hours, a team of USGS geologists conducted scientific and engineering investigations, to help advise with the reconstruction effort.

Details

Date Taken:

Length: 01:09:44

Location Taken: Menlo Park, CA, US

Transcript

- [inaudible]

- Louder?

- Volume.

- The greatness of an institution ends up being dependent on a very few people.

- [inaudible] [laughter]

- How about this?

- [inaudible reactions]

- An institution’s reputation rests remarkably on very few people who provide, in our case, the breathtaking science and also the character of the place. And George Plafker is one of those people. He’s in very limited company and rarefied air. And the reason this is so is that, in 1964, Earth sciences were swept away by the plate tectonics revolution, which changed everything we know about how the Earth works. And, in the USGS, there are perhaps four people who participated in that revolution, and George was one of them, with a profound insight. And that insight was triggered by the Great Alaska Earthquake 50 years ago. And what’s interesting is I’m holding up a science paper authored by Frank Press, later President Carter’s science adviser, and another distinguished scientist, David Jackson at UCLA, who interpreted the 1964 earthquake as being caused by a vertical fault extending from 15 kilometers’ depth down to 200 kilometers’ depth. Six months later, George Plafker penned an article in Science – the longest Science article I’ve ever seen – that showed that, in fact, the earthquake occurred on a very gently dipping thrust fault, all above 15 kilometers – completely opposite to what had been proposed before. And this turned out to be the key to unlock the mystery of the what happens to the oceanic plates that are sliding around on the Earth and need to be consumed somewhere. And what George discovered was that they are shoved under the continents in these colossal earthquakes. In keeping with George’s personality, if you read his paper, he describes the work of Frank Press and David Jackson as an elegant analysis that just happens to not fit some of the data. [laughter] So his gentility, his generosity, shows up, even as a young man. And the difference was, George put his foot on the ground. And George worked as a field geologist when all field geologists who worked in Alaska uprooted their families, went to Alaska for the summer, did their field work, and came back to Menlo Park during the year – something that never happens today. But as a result, he was there. He understood that their hypothesis didn’t fit the geology. And he solved this incredible puzzle, which triggered an understanding of what actually happens to the Pacific Plate as it subducts and occurs elsewhere in the world. But George is important not just for his scientific contribution. It’s also his character. I can’t tell you the number of times that I’ve been lucky enough to have George pop himself in my office with a big smile on his face. What do you think about this? Or, what’s your suggestion for that? And so he’s always eager to interact with others, to give his ideas, to exchange ideas. And this is what makes the Survey a great place to work – that kind of openness, that kind of exchange. And this is something, again, that’s very rare and very important and changes all of our behavior when this happens around us. And it’s also worth noting, since he made this discovery 50 years ago, and that George is perhaps about 83 years old today, that George popped in my office a few weeks ago and said, damn, let’s get some snow on the ground. I got two new knees. I want to test it out on the ski slopes. [laughter] And on March 9th, I will join a number of other of George’s friends on what he calls his over-the-hill ride, where all of his friends ride over Skyline, 1,500 feet up, and then down to the beach on the other side where Doris puts on a great lunch. And then we ride back. And many of us spend most of our spring training to keep up with George. [laughter] So this is another attribute of someone who is always youthful in his – in his vigor scientifically and his vigor personally. And so it’s my great pleasure to present to you one of the Survey’s most distinguished and most important scientists, George Plafker.

[Applause]

- Well, welcome. Finally. [laughter] I’m sorry about the problem. Don’t have any clue of what’s happening. I don’t understand computers at all, and we don’t get along well. [laughter] So, you know, thank you. Well, Ross is one of the – one of the people that makes life really great around this place. We – you know, it’s good – it’s a really good place to be. And he’s very kind. Because, if I can’t find my – you know, whatever I need here, how – you know, I just really am embarrassed about it. I don’t know what’s going on, but we can get along. And so what this talk is about is – as Ross just said, we’re looking into what we call a subduction zone earthquake creator. And the subduction zone is the zone between the oceanic crust and the overlying continental crust when the oceanic crust moves down and underneath the continental crust. And so I had the good fortune to be working in that same area where – you can see up on – kind of the north side and then all around that coast to the east. And the earthquake happened. And so I was in the – in Seattle at a Geological Society meeting with Art Grantz and Rube Kachadoorian. And I don’t think any of us really had any experience working on earthquake studies. [laughs] I certainly didn’t. Rube did a little bit, and Art – I don’t know. But that kind of changed my life a bit. It just added another layer of really young, you know, kind of dynamic geology to what I was doing in Alaska anyway. And I – you know, it’s been really very fascinating, but I still do my usual thing in Alaska too whenever I can. I have supposedly retired. [laughter] And so – what we’ll be talking about here today is the 1964 Alaska earthquake. It was the second largest that has been experienced by the Earth since the time that we’ve had seismological monitoring. And the areas that are changed by changes in level and shifting horizontally, it’s just enormous. It’s hard to imagine, but it’s, like, about a third of the size of California. And so what we’ll be talking about today is some of the things that occurred there. Warping of the crust was a big problem. And we have lots of shoreline in that area, so we had a reference frame for what went up and what went down and what didn’t do anything. And it was a pretty fascinating earthquake to work on. It’s just kind of mind-boggling to think you – you know, you can go up there and – in this enormous place and then – and if you just do the right thing, you can actually reveal some of nature’s secrets. And that was what the – what geology is all about. And so, if you like to play detective games, it’s a good business for you. And so I – it happened that I had been mapping in that area for about 10 years. And – on and off – and [laughs] – and so it was my area of interest in geology, but because I was near the place where this earthquake happened, I guess they just said, well, you know, you know more than anybody else about it. At least how to get around and who to talk to. And so that’s why I got to go. And I also was halfway there. I was at a meeting of GS – Geological Society of America in Seattle. So they didn’t have to pay the full fare from here. [laughter] Well, this great – this earthquake was really great. And it’s – on the Richter scale, it’s a 9.2. And back in those days, the scale didn’t even go that high. It topped off at about 8.5. And so it was called an 8.5 magnitude earthquake until, you know, about 10 or 12 years after it happened. And then we went to a different way of measuring the magnitudes of earthquakes. So it’s kind of unique in the – in the world. And this – the epicenter was right in the northern part of Prince William Sound. And it ripped down 800 kilometers to the south – 500 miles. And we – and then – and up the dip that’s going toward the ocean – up a gentle slope and a faulting – major fault. And that was, at the time, the second- greatest in the world, and it still is, at least in recorded – seismologically recorded history. So it’s pretty unique, all right. And we’ll go through some photos and, you know, show you why it’s so special. Oops. I’m getting the – I’m getting the wrong [inaudible] here, right?

- That left arrow. Yeah. [laughter] So …

- Okay.

- Okay. Just use the right arrow.

- Okay. Well, this map is maybe a little bit confusing to some people who haven’t seen a map like this before, but what it’s – what it shows is the area – these contours show the areas in which the land went up relative to sea level and down. And the up side is toward the Aleutian Trench axis in this region here. And it came – clipped the – just the south shore of Kodiak Island, and then was also – ripped all the way through Prince William Sound. The epicenter was up here in the northern part. And then some deformation extended way out toward the east about 100 kilometers, or 200 kilometers. So a pretty major feature. And behind this area where there was uplift, all offshore, and on land, especially up in the northeastern part of it – the focal region, that land level changes were as much as 38 feet of uplift. And then, behind that area in this big – kind of a curved section, the contours show that it went down. And it went down as much as about 10 feet in there. So what you have is kind of a sine wave – a high uplift and then a little shallower area of subsidence. And that filled all the way from the Aleutian Trench axis – we were a little – kind of conservative in those days. And we only put the area of the deformation going out to sea as far as we had lots of aftershocks. But it’s pretty certain that the rupture broke all the way out to the Aleutian Trench axis. And then, behind that, it extended all the way to the volcanic chain. And the volcanic chain is shown here – these little black stars. And it’s a – there’s a big gap. And then, over in the Wrangell Mountains, it continued. So this is just a big sine wave. And then the game was, where was the fault? I mean, we always – geologists love faults. We all have faults. [laughter] So I – you know, it was kind of challenging when you look at the size of the area and difficulty of getting around and short field season. And so this – just the three of us went up there to look at the effects of the earthquake. And two of us were in Seattle at the time, and the other guy came up with some of our cold-weather gear. And we flew on up to Anchorage the next day. And you couldn’t land at the international airport. Okay. Now. Okay, so what we’ll do is you just looked a little bit at what – the movie is apparently lost somewhere. [laughs]

- [inaudible] when you’re ready.

- Got it? Oh. Well, in a little bit, then. Okay. Yeah, the movie is kind of neat. So I guess … The main – this is just a little kind of background. You know, the reason why we have these large earthquakes is because two parts of the Earth’s crust are moving relative to one another and grinding past each other, and they make an earthquake. And what makes them move past each other is the fact that, down in the – below the crust and in the upper mantle – this lighter-colored part – there is a – it’s relatively brittle material. And then you go below that, and it’s so hot and high-pressure that the materials are plastic, and they’ll move slowly in currents in the Earth depending upon the temperature gradients. And those currents are moving at rates of, like, you know, 4 or 5 centimeters, or maybe 3 or 4 inches, per year. And it was slow, but they have a lot of time because this goes on for millions of years. So basically, it’s the heat – internal heat of the Earth, and there are convection cells, and pieces of the more brittle crust and uppermost mantle are moving with those currents within the Earth. So here’s how it looks. If you had a mid – like, a ridge in the middle, like the Mid-Atlantic Ridge is a famous one. And those are places where there’s an upwelling of magma from the inside of the Earth – molten material. And that comes up and some – and forms these mid-ocean ridges, like the Mid-Atlantic Ridge and smaller ridges that we have off the coast of northwestern U.S. And the – and then they move away, falling on down, and they kind of get – return into the mantle – the deeper levels of the – of the Earth, where it’s – where they get re-melted. And they go down, round and round in these cells. And the cells shift their positions periodically, too, so it’s not – you know, the Earth – and that’s what carries the continents around and all the little bitty pieces of islands and things like that. So basically, all the action that we look at, normally, is just in the crust and uppermost mantle, which is also somewhat brittle. So here’s the way plates move. They can move apart, as you see in the first panel. And that’s the – those are usually the ocean rises where magma is coming up and then spreads out and moves the plates away from the ridge – the mid-ocean ridges. And the other way is that they can move in the opposite direction toward each other. And one or both of them may go – be pushed back down into the mantle. And those are in the deeps – the ocean deeps are usually characterized by one slab going down underneath the other. The oceanic one, usually. Not always. And then the third way is that they move past each other horizontally, like the San Andreas works right here. And all of these make earthquakes, and the only difference between them is that the ones – and any of them could be in the – within the ocean. You can have the same kinds of movements. And we’re always talking about rates of, like, few inch – several inches a year that the – that the Earth’s surface is moving. So there’s lots of plates that make up the crust of the Earth. And we’re on one of the very large ones. It’s this brownish one. The light brown is continental crust, and the darker brown is the oceanic crust that’s moving, more or less, with it. So we’re right about in here now, and so we’re on the edge of the North American Plate. And then the ocean plates are separate. And all these plates are really grinding and moving past each other little by little, and as they do so, they make earthquakes and generate heat and give us a job. [laughter] So we’re just – we’re right about in here. And the two kinds of crust that I mentioned before. There’s the oceanic crust – is made up of usually basalt. It’s dense, you know, rock, and it’s fairly thin. And the – then it is as old as 180 million years. And we’ve – never find anything older than that because it’s recycled back into the – into – down into the mantle of the Earth, where it re-melts and then comes back up again. And so we – I think 180 million years is about the oldest you get. By contrast, the continental crust is thicker and less dense, so it’s floating, really, above the oceanic crust. And it can go back billions of years because it – you know, you’re just seeing accretion to a nucleus of original crust and other pieces being added to that – those pieces. And so all of the old parts of the Earth are in, like, the Canadian arctic region – Archean rocks. They’re billions of years old. And therefore – and they can be involved in all of these processes also. They get faulting and large movements. And so the continental and oceanic crusts – the difference is that continental is lighter. It floats up – it’s higher. And it’s usually what we’re seeing when we’re living on right here. And the oceanic crust is denser and floats lower, and so you – it makes up all the ocean basins, usually, with some exceptions. So this model, then, up in the corner – the right corner shows how the two interact. The oceanic crust moves toward the land, and it could be going parallel to the land, in which case, you have a big strike-slip fault. Or, as shown here, it goes – dips underneath the continental edge, and you have thrust faults along that contact. And then, as it goes down, it gets – becomes dewatered and then heated, and bits of magma come up, and you get volcanic chains. So volcanic chains go with this process of convergence, and the trenches do also because that’s where the initial downward motion starts. So the whole system is made up of a trench, an intervening area of crust, and then an arc – we call them volcanic arcs where magma is being ejected from the melting material at the base of the crust. And it melts because water is being driven off at a certain temperature and pressure, and it enhances melting of the – of the crustal rocks. And they come up as magma and make volcanic chains. So that’s what we start with. And I think that it’s probably enough. [laughter] But the old – the continental crust, you know, we have rocks that have been dated as old as 4 million years. And that’s a lot more than what your oldest oceanic crust is. So the grinding of these plates as they go past one another is what makes the big earthquakes. And that’s what the 1964 event was. So it was the second largest in the world. And the first largest is in Chile and was just four years before in 1960, where about 1,000 kilometers of the – of the margin was ripped by a huge earthquake, and it generated a tsunami that was – killed several hundred people in Japan and Hawaii and all the way across the – you know, across the ocean. Plus what – there were large losses of lives in Chile. But the Alaska earthquake is a close second. So here’s the effect – it shows what Alaska looks like. That’s all continental crust shown in green and light – you know, very pale green. And it floats higher because it’s that less dense than the materials it’s on. And then we have – it’s surrounded by oceanic crust, which is lower because it’s a higher density than the granitic rocks. Okay, now here’s where the video is supposed to start.

[video starts]

[Music]

- Everything was in chaos.

- I’d never seen anything that destructive that close up.

- In 1964, Alaska was shaken by the largest U.S. earthquake ever recorded. Magnitude 9.2. [Music] Shaking went on for over four minutes. 143 people died. Total property loss in 2013 dollars is estimated at 2.3 billion. There were gaping fractures, massive landslides, and the destruction of water mains, gas, sewer, telephone and electrical systems. The epicenter was in Prince William Sound, 74 miles southeast of Anchorage, yet effects were observed as far away as Texas and Louisiana. What the 1964 Great Alaska Earthquake taught scientists was as profound and far-reaching. Initially, no one understood how or why the earthquake occurred. Immediately, three U.S. Geological Survey scientists were sent to figure it out.

- The main airport, the Anchorage International, was closed down because the control tower had collapsed and killed the operator.

- And then we went out separately – mostly separately, to look at different things so we could cover three times as much ground.

- The scientists studied the effects from the air, on land, and along shorelines. They were astonished to find that the surface was disrupted over an area larger than California – 185,000 square miles. Some areas dropped down as much as 8 feet, and others rose up by as much as 38 feet. Barnacles once 2 feet below the ocean surface were suddenly several feet above. Mapping this uplift and down-drop became crucial for understanding what happened. But, with no faults visible at the surface to explain it, even with months of careful observation and field work, the cause of the quake remained a mystery.

- It was right at this time that this idea of plate tectonics, that the surface of the earth is broken up into roughly a dozen different plates and that they move around with respect to each other – it occurred right at the time where this idea was being put forth.

- One of the scientists, geologist George Plafker, considered the quake in terms of this newly- forming theory of plate tectonics. He knew the theory had new crust forming at mid-ocean ridges, but there was no explanation for where this crust went.

- And so the most likely one that came to mind is that the oceanic crust is being pushed underneath that part of southern Alaska at a very low angle, and there was slip on this – on the interface between the oceanic crust and the overlying continental crust.

- These two crusts are converging at the rate of an inch and a half each year. Periodic slip between the crusts produces great quakes, which Plafker called megathrust earthquakes. His realization changed our understanding of these great earthquakes. Megathrust quakes are the largest known on planet Earth. They occur in areas of colliding and descending crusts known today as subduction zones. The uplift and down-drop of large areas from these quakes is a result of the crust being compressed over years of the plates converging. It releases like a spring, which is the earthquake. Seaward areas are uplifted while landward areas drop down. George Plafker identified this pattern common to megathrust quakes in subduction zones.

- The 1964 earthquake was the first megathrust subduction zone earthquake properly interpreted as such. As a result of that, essentially, every other large subduction zone earthquake around the world sort of falls in the shadow of what we learned from the 1964 earthquake.

[video stops]

- So that was just about the duration of the earthquake. [laughter] So it was a long, long time.

- Oh, wow.

- Okay. And here’s what the earthquake did. The area that it occurred in is shown right here in this hash pattern. That’s the area that uplifted, and part subsided during the earthquake. And then you go way on out to – past Fairbanks and in that area is the limit of landslides, avalanches, ground cracks. And then it goes way on out here to – out the Aleutians, where you – it’s almost to Dutch Harbor, which is about – I guess 800 miles. And then all the – it went almost all through northern Alaska and down to – actually was felt in Seattle in sensitive places. So this is a mighty big earthquake. And the hashed area we’ll talk about more because that’s the part that was deformed and is still, in part, settling down, in part, recovering what happened. Okay. So that’s – we’ve seen before, and you can see that it’s a fairly large region. That length of that is 550 miles, and it’s down across the length. It’s about 250 miles on the north end and 150 at the south end. So it’s kind of tapered. But it’s a huge area. Okay. And that shows pretty much the same thing, only it differentiates the part that went down with the pink and the part that came up in yellow. And so the big game was to go looking at all the shorelines and – wherever we could get to them, to find out if there’s any abrupt changes in the level of the shoreline, which would signal a fault. And so we basically covered all of the shorelines in that entire region in the first – well, mostly in the first summer, and then some in the next summer afterward. And then just shows that there are lots of earthquakes in Alaska. This region is seismically active, as you can see. All these little red and blue dots are earthquakes. And they go all the way on out to the west in the Aleutian chain. And it’s by far the most earthquake-prone area in the U.S. [Silence] And this just gives you some idea – the regional setting, but we don’t have to deal with this much. It’s mostly that greenish area where the deformation occurred from the – from the Alaska earthquake. And this is the same thing we saw earlier on, only it’s colored so that the red shows areas that went up, and contoured in meters. And the green is a zero – a zone of zero change. And then the blue is a – is a – shows where there was subsidence relative to sea level. And everything we had to do was relative to sea level because that’s the only benchmark we had. It’s such a tremendous area. But you can almost always find critters living on the shore that would tell you where you were in the – in the tidal zone. So the main thing I wanted to show here if that this little island – and it’s a big island, really [laughs], but it’s pretty small here, there was – this is a place where there was an actual fault rupture. And this rupture is superimposed on a big, broad, sine-wave-shaped uplift and subsidence. So the main – the major uplift in this area was up to 36 feet. And in the subsided area to the – to the – shoreward from there, it was, like, 3-1/2 meters – 10 feet. This map started with feet, and now it – then it changes to meters, and now I’m – got to get it back to feet again, and it gets me very confused. [laughter] But you can see, there is the – the star is the epicenter. The epicenter really doesn’t mean all that much. It’s just the place where the rupture starts. The rupture ruptured for 550 miles to the south-southwest. And this is, if you took that zone of uplift, which is in red, and the blue, it would be the subsidence, and you kind of rotate them and flip them, this is what it would look like if you superimposed it on the northwest coast of the U.S., where we have a similar kind of a subduction zone earthquake – the Cascadia Plate. And it’s just to show – it extended the full length of Oregon and Washington and up into Canada. And here you can see these little bathtub rings on the shoreline. And over here, we’re pointing to one little bench and then the next one. And what those are are vegetation rings. And they – that shows pretty much the amount of uplift at that shoreline. And that’s what we used. We basically – within a foot, or a couple of feet in places, you could determine how much change there was vertically just by these critters who all knew where they belonged in the tidal zone, and a lot of them came out very abruptly and died. [laughter] And here’s a similar situation. Actually, the barnacles are down at the bottom of that, just a little bit above the water level, which is at high tide. So these barnacles here were – are all dead, but they’re – you know, this is high tide, so it looks like they shouldn’t be dead. But that’s – what we did is basically go – use these as an indicator of where horizontal was before the earthquake. And then you can measure where – and sea level – high sea level is after the earthquake, and that’s what we – how you countered up the amount of change in level. And, in the places where there was faulting, it would fault that – those bands, and you would have uplift – one side uplifted relative to another, and that’s how you could find the faults. Only a few faults were found. The big action was down at the bottom of the crust where the megathrust lived. So here’s a – one of the reefs that was uplifted a lot. It was right in that area of major uplift on Montague Island. And it was – right here is probably 35 or so feet of uplift. And those are kelp that are on the panel on the upper right. And a bunch of starfish who – unlucky. They couldn’t hike fast enough to get out of the – to stay in the water when the land was uplifted. But you don’t see many fish in those little ponds, so you get an idea of how fast this came up. You know, it was kind of – it was probably moderately slow, actually. And this is a fault that runs on this one bay at an island – Montague Island. And that’s the fault running right across there. And this side here is up about 35 or so feet. And this side is up also, but only about 18 feet. So you have a fault scarp between them. And this was fairly minor, but a very nice fault. And here’s a closeup of it. It goes right along this – makes this scarp here, and then you can see in the background, there’s a beach, and that’s offset where the yellow line is. And that line is lined up with the trace of the fault where it goes over the ridge. And so it gives you a dip on the fault. And this was somewhere around 60 degrees. But both sides up. That’s called an uplift fault, and they’re very rare. [laughs] So here’s a – here you can see the – in the background the two arrows – one on the same – what used to be the same level. And that’s about 5 meters – a little more than 15 feet. And, in the foreground, you can see that the – that the fault scarp is breaking up and falling down, and you really can’t tell that it really dips into that scarp. It doesn’t dip toward you. So it’s just a fault line scarp, in geology terminology. And here goes another fault, which is really the bigger one. And it cuts across this beach here. And the arrows point to the base of a slope and the top of a slope that was offset. So it – and it makes that – made that pond, and then it goes on out to sea. And this was four months after the earthquake. So it’s kind of degraded by the – by erosion. And George Vancouver saw this same phenomenon, and he was a good enough observer to put it in his log book and say that – note that the seas – something’s happening, and the sea is making rapid encroachments. Because there’s some dead trees all along this beach, and those were from a previous earthquake. Their roots are well down in the gravels, but Vancouver saw them. And those stumps are, like, 700 years old. So what this shows is what we call paleoseismology, which is ancient seismology. And it’s a way of kind of determining whether – you know, where old prehistoric earthquakes exist. So, from the top to the bottom, you can see there’s probably – there’s eight layers plus the uplifted 1964 surface, which is at the top. And so there’s – you can then get a recurrence time for all the intervening – for the – for all these earthquakes, and it works out that there’s about 630 or 50 years, on the average, between events. And that’s one of the tools we use to find out how many earthquakes you’re likely to expect in a place like this. And the same thing happens in the opposite direction where we have terraces. These are called marine terraces. There’s uplift – the lower arrow is on the present-day high-water mark at – this is high tide, so there’s really not much of a terrace down there, but it – at a low tide, it goes way out. It goes miles out to sea. And then the higher one is on the – like, a third terrace up at about 33 to 38 meters. And there’s a whole flight of these terraces. There’s five of them on the island. And four or five of – six of them – four – yeah, there’s six of them on the island. Five out of six are – correlate with the ones on the mainland that we see in the Copper River Delta area. The sixth one just doesn’t fit yet. So it just shows that these very big earthquakes are – takes a long time to store the energy, to make an earthquake as large as a 9-plus magnitude. And that’s just a picture of the island, and it’s got all the terraces colored in and – like geologists like to do. And it’s pretty. And that’s it. [laughter] And it showed – just showed where all of the samples were that we used for dating those events. And then this is a – this is what – if you plot up each of those events and how high it is above sea level, you get a kind of stairstep plot like this. And so that gives you an idea of the – you can measure the – how much time and uplift per event. And we found from this last one in ’64 that you only get about half of it in the – so, like, this is from here down, that’s about half as much uplift as all of the older ones. And that – what we’re finding is that you would go back once in a while and look at those things, that they – that they’re still coming up. They just kept – maybe half of it during the earthquake, and then the rest of it is just creeping up. So it will probably go until it catches up to the – to all the others. And this is – one of our benchmarks is this old World War II ship. And it has the barnacles way up to where the hand is on this fellow here. And the bottom is actually below the level of the ship. You can see water in the hull. And that’s kind of our marker for, you know, tide gauge. And this is – this is just one of – the trace of the fault as it runs inland. It’s one of the bigger ones. And you see all of the landslides along it. There are just – it’s just masked by landslide debris. And just was shaken real hard. And here’s an area where you – in the opposite direction where – on Kodiak Island, and the areas north – to the north. There was a lot of subsidence, and so this area was subsided about 5 feet, and at high tide, it’s inundated. The road is not usable. And here’s a kind of good marker. It’s an area of subsidence here. You kill all these trees off, and then if you look on them, it’s neat. There’s barnacles on the trees and all these little Littorina and other shore-type mollusks. And it’s just that that area subsided about 6 feet. Okay. Back to this one. We don’t have to be here. But you can just take another look at it, and you see that what this really is is a – is kind of an uplift – a big peak on it where it goes across Montague Island, and then it goes back down. And the average looks, like, 3 to 3-1/2 meters for the background. And then this one area of very steep uplift. And then it goes into the subsidence to the northwest. Well, that’s – we have reason to believe from the – from the way the tsunami acted that this faulting that we see on Montague Island extends way out to sea at least as far as shown here. And then it may go all the way to Kodiak. Because they had very early arrival times of waves at this place here called Cape Chiniak. And that’s a fairly sizable earthquake – fault. It’s, you know, a few hundred miles long. And this is a section through that margin. And if you look at this, what you’re seeing in this bottom panel is the continental margin. This is an island out here – Middleton Island. The trench – Aleutian Trench is right off there. The faults we were just looking at are on Patton – or, Patton Bay and Middleton Island are here. Middleton is over here. Sorry. And [inaudible] is on Montague Island here. So we’re seeing some fault activity. These are inferred – just the – like, Middleton Island’s because it came up, and it’s not possible to bring – pick up the island without having some kind of fault motion. And the epicenter would be right down at the red mark. So the blue line shows the displacement down in the area toward the continent – toward the land. And then a big pooch up to this – Montague Island, where we got up to this 36 or 8 feet. And then – but, again, this is – both sides are up relative to sea level. Here, the other side is up around 5 meters. So then – we don’t know what happens offshore. The dotted part is one type of path that the uplift and subsidence could take. But we don’t know for sure. The only reason for putting it out there is that you do have Middleton Island out where the 3.5 meters is. And it’s still coming up at a pretty good clip. It’s about – a little over a centimeter a year since the earthquake. And that’s just an overall view of the situation and some slices through it to show that it’s got to be a very low-angle fault that’s going generally landward from the Aleutian Trench. And that the seismicity is pretty much confined to the upper part of that panel and of the faults breaking to the surface. And you have a zone, actually, of fairly high seismicity right pretty much where we speculate that there’s an extension of the faulting on that one island – that Montague Island. And so this is one kind of a – this is the kind of thing geologists do. I don’t know if anybody cares, but … [laughter] It’s just basically to try to reconstruct in a simple way what you see there. And so this – we know the continental crust is underlain by a basaltic crust that’s pushing in from the ocean. And these faults probably all – these are speculative with a broken line. And these faults probably [inaudible] down into that thrust, and then that whole area is rebounding seaward after it gets kind of compressed over many years – hundreds of years here – by the movement of this mantle beneath it. So it’s basically – it gets carried along and carried along until it’s strained too much, and then, bang, it snaps back. And that’s what the earthquake is. And, in this case, the slip on that earthquake was, you know, looking at something like 30 feet or so, at a minimum, and maybe 60. We can pass that up. It’s New York Times’ take on the whole situation [laughs] from 1964. And this just shows that area we have – where the maximum slip was on Montague Island up here. Clearly extends out this way. And one other way of finding – of figuring that out is the time between the earthquake and when the waves arrive at the shore. And, you know, so the closer the source is to the shore, that’s what – it’d be, like, in Kodiak Island. And then in this area, it actually comes ashore. And right here, there was a pretty good arrival time at 19 minutes, which is very short. You can’t run far in 19 minutes. And this whole area – this yellow was uplifted relative to sea level. So you have a big, broad uplift that makes a tsunami, and then a peak on it that makes an even bigger tsunami, but local. And that’s the ones that come back and whack the shoreline. And there’s not much warning time, and they are – it can be really high because these little fault-bounded segments of the crust can be – you know, move a lot of water. So here’s what happens in Kodiak from the tsunami waves that were generated. And this is a whole nother story about – near Valdez. It’s a very steep-sided fjord. And these two places where there are red X’s are the ends of a terminal moraine, and that goes – drops down into water that’s about – that’s 104 feet or more deep right near the – near there. So it is big submarine slides. The slides generate waves. The waves come back and whack the shoreline. And they’re very dangerous because a lot of those things happen right during the earthquake. And so there was some – there was a prospector – Anderson – Henderson who lived across here in Anderson Bay. And he got whacked – never – no sign of him after the earthquake. And all these are just little arrows pointing to the direction the wave was going based on how trees and brush fell, and also the size by a number that we made up just to get a qualitative handle on the size. So here’s what happens when one of those little waves came back and whacked the shoreline after probably a few minutes. And, you know, this hill up here looked just like what’s in back of it – all of those trees. And it just stripped the trees right off and just stripped everything off – the soil and vegetation all the way down to the rock, the whole way – all through here. And that’s 80 feet high. And here’s what it looks like on top. And any – you see those blocks of rock here? One I think we estimated at 800 pounds. And that’s 27 meters above sea level. I know it came from sea level because there’s barnacles on it. [laughter] We estimated 800 kilos. Not pounds. So there was – you know, that’s the kind of thing that happens, where we generate – there’s different kinds of tsunami. Everything is called a tsunami, but there are some that are real – tectonic things where the uplift of the whole surface of an area, and deep-seated. And then there’s others that – like this – like some of these, that there’s shaking, and there’s a landslide, and the landslide makes the wave, and the wave comes back and hits the shore, and they call that a tsunami. And it can be very confusing. Anyway, what we learned, of course, is that you stay away from those places. [laughter] And then, if you can’t stay away, run like hell as high as you can get. Because a lot of those waves are just generated by the shaking during the earthquake, and then, when they go, it’s pretty fast. And then they’ll generate a local wave that will come back and whack that shoreline. So – or the – and some will go across the fjord and – to the opposite shorelines. So it’s a – they’re really dangerous. Okay. So all – what was learned? We learned that you can – yeah, you – that you can make big waves. [laughter] And that the ocean crust is being pushed underneath the continent there in Alaska. And that’s what makes the earthquakes. And you have clear evidence that there’s more than one kind – that there’s these big broad ones that involve the whole continental shelf, and then there’s – on top of those, sometimes you’ll get these splay faults, we call them, that come up more steeply. And that’s why they can rise way higher than the – sort of the general level of the uplift. And that’s what determines how big a wave you're going to get. But those waves don’t travel very far. They’re usually pretty narrow. And we learned a lot about tsunami warning, that you don’t just say that – wait until you get a warning on your radio. When you feel an earthquake, and you’re near water, run like hell. [laughter] And there’s a pretty good tsunami warning system in all of these places now. You know, they all have sirens. And they do give a loud warning whenever there’s a possible tsunami generated. Well, that’s enough for it. And thank you for your attention.

[Applause]

- I know George would be happy to take questions.

- Please use the mics. There’s another mic on that side. [Silence]

- So thank you very much for the good talk. Was this mechanism similar to what happened in the Japan – in the big Japanese earthquake recently? The one that caused the Fukushima incident?

- I don’t know what happened. I’m not sure anybody does yet. I mean, there are several theories, and one – and that – one is that it’s a gigantic landslide that went into the deep water. And the other is that there is a separate little fault-bounded block that somehow got pooched up. It’s a real problem. I mean, you know, the width of that zone that ruptured in that earthquake is a couple hundred miles – kilometers, I think it was. And that’s only a very small area that caused all the trouble – the big trouble. And I – you know, whenever you see something like that, you suspect a huge landslide.

- Although I think that – you know, the simplest answer to the question is yes. That’s another megathrust event of about the same size. And George is talking about the peculiarity of its huge tsunami that might be caused by an undersea landslide in addition to that subduction zone.

- Thank you.

- Next question?

- Could you give me a history lesson on how the geologists reacted to the plate tectonics in that area? I mean, that timing? When did everybody believe in … [laughter]

- Plate tectonics?

- Yeah.

- Well, it depends on your religion, I guess. I don’t know. [laughter] But there are some who still don't. But it was – it took a while. And it was – I think, you know, there was explicit descriptions of all features that required plate – big plate tectonic interactions all the way – yeah, you had them all the time. But the bandwagon just started about the time of the Alaska earthquake. And it was really something. I mean, everybody, all of the sudden, wow, they had, you know, all kinds of evidence that things like that could happen and did happen. And, yeah, it took probably until into the 1970s until most of the – you know, we have – geologists are a strange bunch anyway, and, you know, [laughter] they – a lot of skeptics. [laughs]

- Let me just amplify. George was telling us at lunch that, at the time, most people believed that the Pacific Plate was rotating counter-clockwise, and that would explain the San Andreas motion with the Pacific moving to the north. And they thought that the great 1960 Chile earthquake – the one that George mentioned was even larger – was also a strike-slip earthquake, which we now know to be false. And so they were very happy to make this earthquake a strike-slip earthquake as well. So, in that scenario, no crust is created at the ridges, and no crust is shoved under the continents or the island arcs. So that was completely false. But it was motivated by the discovery, really, of Bob Wallace here at the Survey that the San Andreas had cumulative slip of hundreds of miles. And therefore, the only explanation people could come up with is that the Pacific Plate was spinning in a counter-clockwise motion.

- Well, thanks again for such a great description of your experience. I seem to remember something – Turnagain Heights?

- Turnagain, yeah.

- And could you comment on what happened there and why?

- It was just a landslide that went for miles along the bluffs in a very extensive layer of sediment called Bootlegger Cove Clay. And apparently it had this property – a sensitivity that, by shaking, it loses it strength. And large blocks of this just slid out into the arm. And it’s a pretty intriguing fault because they – you know, they came off – as the Earth – the shaking continued, you know, one piece would slide off, and the piece behind it, and the piece behind it. And it cracks way back – going way back inland. And it was – you know, that’s why – one of the problems with this earthquake being four minutes of hard shaking. It had a lot time to wreck that whole Turnagain Heights area. But it’s just basically a sub-horizontal plane on which the sliding occurred. And you don’t want to be on that. [laughter] It only …

- It was a housing development, was it not?

- Pardon?

- Was there a housing development there?

- Yeah. Oh, yeah. That’s the Turnagain Heights …

- What was …

- … subdivision. No, the houses don’t last when they get ground up by [laughter] these big blocks of …

- Did that result in much loss of life?

- It didn’t. Mostly it’s because the houses all were wood, and you – they were lightweight and, you know, they were floating on top of this – all of these sliding blocks. And the only people who got – were killed were probably some who ran out of the house. And then they fell into these opening cracks and – I don’t know where – were recovered. But it was surprising. It was only three – I think three deaths in Turnagain Heights.

- Thank you.

- But it is a pretty big shambles. That was what was at the beginning of that movie clip, when all – everything looked like it had been bombed out. That was Turnagain Heights.

- Yes?

- Oh. Looking at that global plates map, I was struck by something. I’ve got scraped up by oceanic crust up the hill from my house, and that whole Beringia area between Alaska and Siberia and stuff is flooded continental crust. But are there extensive areas anywhere in the world where there’s elevated plain oceanic crust that you can go and see and see what that looks like?

- Yeah. You just go up to the north side of the Golden Gate Bridge. And those are pillow basalts there. The good old deep-ocean rocks. [laughs]

- It’s a beautiful place to visit. Well, thank you very much. We’re really glad to have George here tonight talking about this momentous discovery.

[Applause]

[inaudible background conversations]