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Harold Tobin. Harold's research focuses on pleasure tonight to introduce geoscience professor
what's going on on the edges of earth's tectonic plates.
These are places that have
active earthquakes and volcanoes.
co-leader of an international team of scientists who are And in particular, Harold is the
interested in and doing research on the Nankai trough, which is
off the coast of Japan. And what this team is doing is
actually drilling into the active fault there, taking out
rock specimens and inserting
instruments that can help them understand what makes earthquakes begin.
And tonight, he's going to be talking about the recent
earthquake and tsunami that happened in Japan.
With that, I would like to introduce Harold Tobin.
( applause ) >> Harold Tobin: Thanks.
Thanks very much, Brooke. And thanks to both Wednesday
Nite at the Lab series and the Geology Museum,
of which Brooke is the assistant
director, for sponsoring this talk tonight.
my research and that is exactly what I'm working on. She told just you a little about
is a different part of the The region that we're doing the drilling project in
offshore region of Japan than the March 11 earthquake happened on.
So this is going to be an interesting talk in that I'm
mostly going to tell you about things that are not my personal
research. In fact, it's going to be kind
much as I can of the science of a current events talk. But I'll try to bring you as
sort of clearly as I can for that has come out of this earthquake since it happened, and explain it, you know, as
people who are maybe not geophysicists.
about it as we go along. I'll be happy to take questions
But so, I titled it, you know, the March 11 Earthquake and Tsunami, what happened and why.
What I would like to do is
really explore the events of that day, and actually the day
days after, and the times since then, focusing on the main before, and then a number of the
planet to make that earthquake earthquake of course that happened, what occurred in the
occur, why was it so big. As you have probably heard already, this was the fourth
largest earthquake that's been
recorded since we've had seismometers active on the
That's since about the 1890s, late 1880s or so. For 120 years, this is the planet.
ever occurred. fourth largest earthquake that's
to this earthquake. I can also tell you that it is before shock and aftershock sequence that occurred related
the best recorded earthquake that's ever occurred of any kind
of magnitude like this. We have an incredible richness
of scientific instrumental recordings of a whole variety of
types, and I'll show you a bunch
of visualizations of some of the data. We'll talk about actually the
warning system that is active in
Japan and how it performed. We'll talk about the tsunami that occurred, which of course
was really the source of the
vast majority of the terrible loss of life in this earthquake, and most of the source of most
of the destruction, including the key part of the damage to the nuclear reactor that still
So, I'll focus on what happened locally, and then I'll also talk has people pretty worried.
which is the travel of the about what you heard about on the news a lot at the time,
tsunami waves across the entire pacific basin, and how we know about that, and what some of the
forecasting, how it's actually
and tsunami, and say well, you done. We'll take a historical perspective on this earthquake
may have heard that scientists were surprised by the magnitude of this earthquake.
Actually, that's true, and I'll explain what that means and why.
Japan, but were surprised by It doesn't mean we're surprised by earthquakes in northern
some aspects of this particular one. It's actually causing us to go
back and take a second look at
some of the really fundamentals models for how these kind of earthquakes work.
Then I'll sort of put it in some perspective at the end.
little bit of time, in the I may talk a little bit about our research project if I have a
Nankai trough region of Japan. So with that, let's dive right
Here is a Google Earth image, of in.
course, of the Japanese islands. I cut Hokkaido off a little bit up there.
But you can see a couple of key features. Besides the actual islands of Japan themselves, the most
obvious thing on the map is all these yellow dots everywhere. That is the first week of the main earthquake and the
aftershocks above magnitude 6.
That's a map of all the magnitude 6 earthquakes that happened in the region.
Every single dot is a magnitude 6 or larger earthquake. You can see that, the largest one, they're scaled according to
the size of the earthquake. The largest one is the main earthquake. It's epicentral location on the
planet, so the point on the earth's surface above where the earthquake actually occurred, it
24 kilometers, 15-18 miles down in the earth's crust. You can see the whole region of oaftershocks, which is actually
illustrating for us the region
of the earthquake fault that ruptured. I'll explain what I mean by
that. So, an epicenter is just sort of
a point where the earthquake waves began to emanate from.
But the actual portion of the fault that slipped was so large that it extended for about 400
Japan and about 200 kilometers kilometers along the coast of
in the perpendicular direction defining a whole area of the
And aftershocks actually end up mapping that out pretty well. The other thing that you can see fault that slipped.
bathymetry, right, the in this image is the sea bed
topography of the ocean floor. You maybe have heard of the oceanic trenches, we'll get into
them in them a bit when we talk about some of the basic plate tectonic questions. This region is called the Japan
trench. This is Honshu Island.
Some refer to it as Northern Honshu.
In Japanese, the region is
called Tohoku. It's been called the great
That's sort of the official seismological name of this Tohoku earthquake.
actually a second trench earthquake of 2011. You can also see there's
down here. This is the region called the Nankai trough.
The studies that I'm doing with the offshore drilling project are actually right down in here.
magnitude 8 earthquake, but we're in a different region from We're looking at a likely future
So, I'm going to start with some where that earthquake occurred. Okay.
real fundamentals. And bear with me for a second,
everybody is kind of on the same but let's just make sure
page. The first question is just fundamentally, you know, what is
an earthquake?
that we feel, the thing that Well, it's really two different things. One is that the earthquake waves
shakes the ground if you standing in an area near an earthquake.
How many people have felt an
earthquake before in their lives?
That's pretty good. When I talk to undergraduates, Oh, most of you.
there's not nearly as many who've felt an earthquake around
here. It shows that some life experience is valuable, right?
The waves that you feel are the vibrations of the earth, ( laughter )
but they're not the actual earthquake itself.
Because the earthquake itself is really the rupture or the break in the ground that occurs during slip on a fault.
So we say, what is a fault? Well, a fault is sort of just simply a flaw, or why we call it
crust where two very a fault, a break in the earth's
large-scale, as large as the entire depth of the crust,
are pressed against each other in these kinds of earthquakes,
with a lot of stress, because they're down in the earth, there's a lot of pressure,
but tectonic forces that
I'll explain in a moment cause those ultimately
So they can stick together to break and fail.
Now if we look at a little and slide past each other when they're stressed.
animation of just a little chunk of the earth here, and I have to
button, because some bug remember not to push that laser
in Power Point means it stops the animations from going. You can see is that the rupture
is somewhere down in the
That can be felt at great sudistances, hundreds, evenat trthousands of kilometers awaye the seismic waves that you feel.
And of course, the seismograph from the earthquake.
is just an instrument that measures the displacement of the
measures the velocity or the ground, or sometimes it actually
down, or side to side. acceleration of the ground, which are just related to the displacement, either up and
We usually measure north-south or east-west, so we get three components of motion for a
3-dimensional motion of the ground. We talk about earthquake as an
I want to explain what I mean just a little bit when I say elastic rebound process.
can bend, right? that. Rocks might not seem like they
A rock is sort of a brittle thing. It just sits there, and if you
stress it hard enough, maybe you
talking about the thickness of the tectonic plate with all But when we are talking about miles into the earth, we're
perhaps area, rocks are quite bendable. And in fact they're elastic, in athe sense this is elastic.
I can take the rigid stick, but I can bend it.
back to the original shape, right? Elastic means that I can bend it, but if I let go, it pops
is that how it actually--? >> When you say east to west, or north to south,
>> No, that's just how we measure three components of the motion to rebuild
what the actual motion was, which could be could be in any arbitrary direction. We measure up and down,
north and south,
and east and west. >> It could be northeast, southeast?
Absolutely. Yes, any direction, that's right. So, if we think then about
the elasticity of the crust,
basically we know that there are these tectonic plates that form the surface of the earth.
There's a whole series of tectonic plates, and they're in motion relative to one another. So, if for a second,
the floor is one tectonic plate,
direction along the floor, and this thing is another tectonic plate, and it's trying to force its way in that
if I push on it, it slowly bends, right? I will try hard not to
break this thing, actually. But tectonic forces move very slowly. We measure plate motions
in a few centimeters per year,
maybe up to 10-15cm per year. It's about the rate your fingernails grow.
If you let them grow for a whole
year, that's how far the pacific plate has moved over that time. But it's slowly and inexorably
over centuries building up the
friction along that fault line stress and it's stuck, right? The rug is holding the stick. And that's the same as the
between the two plates. So eventually that builds up and builds up, and the strain,
just like I'm an archer pulling a bow back, is building up more and more stress and eventually it pops, right?
I overcome the friction with
Okay. theSo, let's go on from thereh. That's an earthquake. That pop is the earthquake.
can happen anywhere. a little bit. Earthquakes, as we know,
Some of those earthquakes you guys felt might have been ones Illinois, right, or one--
There's very few
recorded history in Wisconsin. in Wisconsin. We have not had a magnitude larger than 2 or 2.5 in
I might be wrong about that. But certainly not bigger than 3.
anywhere. But the fact is the vast Anyway, earthquakes can happen
but the edges where two of the Earth's plates meet. That's why we call them plates. midThey tend to be rigid,s,
and translating or moving relative to one another.
than magnitude 6 again, but for an entire decade. So this is Okay? of all the On the whole planet.
We won't worry about the depth
for the moment, but every little dot on that image is a single earthquake
that's mapped over that decade. You can see that they don't occur randomly everywhere, but
And in fact, this is part of how they occur at specific places.
the story of plate tectonics was found out, because they observed
associated with the mid-Atlantic that these earthquakes were
ridge. That's where the plates are spreading apart as you've heard,
opening up the Atlantic Ocean.
But most of the earthquakes, in fact, 90% of the earthquakes actually happen in these belts
where you see much thicker
In fact, those are these regions numbers of individual dots. And those are right next to those oceanic trenches.
we call subduction zones. A subduction zone, a big word. All it means is a place where
one plate is converging on another plate. They can meet and they can sort of buckle and rumple, but when
one of them is an oceanic plate and it's low, it's actually very dense, compared to the continents.
So what it does is, it tends to,
one plate rides over the other, and the other one descends descends back into the mantel
of the earth, ultimately to be
around what's called remelted and reincorporated into the interior of the earth. So all these earthquakes all
the Pacific Rim of Fire are subduction zone earthquakes. That's where most of the
earthquakes occur.
You can see them along Central America and South America, let me get
my geography right. The Aleutian Islands, Japan,
and so on, around the Pacific. So, subduction zones
are the big player in terms of plate tectonics
on the surface of the earth. Here's a cross section that kind
of illustrates what those are like. We call the crust, plus the upper part of the mantle
below it, but the rigid part
of the earth's upper region, lithosphere, below that,
partially molten material. it's sort of got some
It flows like taffy, slower than taffy,
This rigid plate goes down but it's very viscous.
beneath the overriding plate. In the case of Japan, this would be the Japanese Islands,
the Pacific plate out here
in the region. The trench occurs at the point
over and dives back down where the plate literally bends
into the interior of the earth. Eventually, that plate gets to a depth of about 100 kilometers
or so, and that actually
is a region where it gets hot and high pressure enough to melt material, and that fuels
the volcanoes.
That fuels the volcanoes of Japan. That fuels the Cascades.
Mt. St. Helens and Mt. Ranier are exactly the same situation
too hot for big earthquakes. in the Pacific Northwest. But down there, it's actually
that frictional behavior, Tlike I showed you on the rug,. so the plates stick together. What we see is that this region
that locks up and builds up that stress.
but their boundary is stuck, The plates just keep moving and moving, and moving,
and then it breaks. That's when the earthquake occurs, and that earthquake can
spread and propagate along
that region, in fact along the length of it, but also
and ultimately move the sea bed to generate the tsunami. up towards the surface,
in northwestern United States, I'll get into that in a minute. >> This formation is kind of the
but we don't see that type of earthquake activity
That's right. And you know what? you see in the pacific.
really important You've hit the nail on the head for something that's actually
in our understanding. You see, you know, lots of earthquakes there,
lots of earthquakes there.
it's kind of a gap. For a long time, we thought, the Pacific Northwest in this region right here,
or scientists I should say thought, it was a little
before my time. After plate tectonics came
around in the late '60s, early '70s, it was thought something
was special about the Cascadia subduction zone, and it slipped down without having earthquakes.
There's been virtually
no earthquakes recorded on the boundary. There are earthquakes in Oregon
and Washington, but they are shallower ones.
It turns out that it's virtually certain that there was
a magnitude 9 earthquake
was discovered through some really clever work that the Tcoastline had some unusual interesting one, in that it
bunch of trees along the coast subsidence to it, where a whole
the year out of that, all up and down the coastline of They could do the tree ring dating and get approximately
northern California, all the way to Vancouver Island.
Then there was a tsunami in the historical records in Japan that had no known earthquake
It was called an orphan tsunami in the historical records in Japan. So even though there were no
people with written records,
1700, at about 9:30am, there were Native Americans in the region, but no Europeans in the Northwest, on January 29,
of really interesting sort of, we know there was a magnitude 9 earthquake. And looks like from other kinds
almost like archaeological work, we call it paleoseismology, digging holes in the ground,
looking for the characteristic
telltale deposits, we know that that's probably happened about every 500 years over
the last few thousand years.
time for that to happen again. It's been 310 years since then, so, plus/minus error, we're right within in the range of
That's why the Northwest should be worrying about tsunamis and earthquakes, and in fact
is worrying about it, and taking some steps.
Okay, that was a great question. I have some slides about that
later, but it was a good time to answer it now. Anyway, so let's move on. The uplift of the sea bed during
the earthquake is the cause of the tsunami, fundamentally.
I'm going to show you how that works in a few minutes.
But first I want to show you a
one step at a time. lWe are back to northern Japane ihere.. Again, here's a map of the early
aftershock sequence.
There's the main earthquake, once again, in this location
Here's the same thing, but it's depicted as a function of time. So these are dates in March, and all those aftershocks.
north and south. and then just the latitude,
The main earthquake is here, and you can see what happens. That earthquake occurred and
then all these aftershocks just started lighting up that zone.
a big patch of earth's crust And what happens is the earthquake slips, and it slips
along the boundary between the two plates. Then once that happens,
it's sort of like the fault is in its new configuration, and
needs to settle in a little bit. It's kind of like you sit down
in a chair, then you've got to
It's got this sort of fresh scar get yourself comfy. So the fault has suddenly slipped a whole lot.
to it, and lots of little stresses pop off lots and lots more earthquakes.
That's what aftershocks are.
Aftershocks are a completely normal occurrence they happen in
decaying time series after an earthquake. Rule of thumb is you can always expect, you can virtually always
expect at least one aftershock
So for a magnitude 9 earthquake, of about one magnitude number lower on the earthquake magnitude scale.
we expect at least one about magnitude 8 aftershock and then kind of 10 times more for
magnitudes 7s and so on, 100
times more for magnitude 6s. It turns out this has followed
There was a magnitude 7.9 aftershock a few minutes after that pattern pretty well.
the earthquake actually, in fact, so close in time that
in Tokyo they felt the waves
just kind of run all together from those two different earthquakes.
But more interestingly for this earthquake, there was what we call a foreshock. Foreshock, aftershock,
they're just terms defined on the basis if you have a big earthquake, that a littler ones that come before it on the same
fault are foreshocks, and littler ones that come after it are aftershocks.
a foreshock when this magnitude 7.3 earthquake happened a day or so, two days beforehand. But it turns out it did happen
in just the same region as the
main earthquake did, and it was probably that sense that you know, if I took my stick
and I took it all the way to breaking it, we'd probably hear it creak and pop a little
I'm not going to break my stick. right before it snapped.
But that creaking and popping just before it goes, the initial giving way of the fault zone
is a foreshock. So we should be able to see those foreshocks and predict
them, right? earthquakes on the basis of
big earthquake that was coming. We shThe problem is that that hstatistically, we never know that this was a foreshock for a
whether it is a foreshock for a bigger event or not. when an earthquake happens
When that earthquake happened, people knew there was a long
history of magnitude 7
And people have tried very hard to use foreshock information to jupredict earthquakes, and itne turns out it just doesn't work.
You can't make a statistically
useful prediction based on any particular earthquake, until the
go back and say ah-ha, that was a foreshock, right? ( laughter ) bigger one happens, and then you
The old adage about prediction Scientists are smart, you know.
is, it's a very thing to do, especially about the future.
instead. So, we try to predict the past
Okay, so let's look at what actually happened in the earth's crust on the fault zone.
It turns out that when the waves
as you know, right? pThe seismic waves travel earthquake, they are recorded literally all over the world,
all around the planet. We'll look at that in a second.
We can use computer models
planet, to backtrack to the source of the earthquake was. aIt arrives everywhere, and you of seismographs all over the
out, so you can basically calculate backwards in time to can imagine the wave spreading
back in its position, essentially. get back to the source of the earthquake, kind of triangulate
They fit the wave forms. Well, there's more to it than that.
There's some very sophisticated modeling that goes on. But what can come out, is
actually a pattern of the slip
on the fault. This is one of several earthquake slip models, but it
basically suggests the star is
where the epicenter was. And the sort of big blue
that they fit in the model that you have to imagine going down rectangle is actually a plane
the surface over here. into the earth at an angle. So it's like it comes up to near
It's at about 40 kilometers depth under the coastline, and so it's a plane dipping down,
sloping down into the earth's crust.
It's actually the boundary between the Pacific plate over
here, which is going underneath Japan at 8.3 centimeters
happened was, the slip started per year. Anyway, what it looks like
there, but it spread out over about 400 kilometers, or 350 kilometers.
The remarkable thing about this earthquake was that it generated
initial magnitude of the very large seismic waves. That's how we can calculate the
area that the fault slipped, and earthquake, but we actually estimate the magnitude in total of an earthquake nowadays by the
slip. It's an energy calculation, how themuch work is done by theh, the frictional resistance to
That energy calculation suggests earthquake.
the moment was something times 10 to the 22nd joules.
But in particular, it shows that It's a big number.
the slip over this large area between the two plates in that 1-1/2 minutes or so,
2-1/2 minutes or so,
what, 160 or 170 feet that those two chunks of rock slipped relative to one another, That's 100 to--
slipped in a few minutes. That's remarkable, and built up over hundreds of years
If we look at this, this is an interesting animation. thatIt's one of the backses the tsunami.
energy recorded at seismographs all over the USA. I should actually restart it, so you can see what's going on.
But seconds going by here.
It basically shows the The slip starts off here, maybe you can see the coastline just there.
different patches of the fault, we had started at one place, and that kicked off another
part of the fault, and that kicked off another part of the
Actually, there were times fault and it's spread out over this whole region.
nothing much happened, and then another piece of the fault kicked off.
It was a very dynamic event that took a lot of time.
The slip, if it holds up We're up to 500 seconds, or so, having taken place down here.
of 30 to 50 meters, is the largest slip recorded in any earthquake.
There's been some larger
earthquakes, the Sumatra earthquake in 2004, the one that
that was actually an earthquake that had a larger area. It slipped over something like caused the Indian Ocean tsunami,
to the Bay of Bengal, but it 1500 kilometers, all the way up
only slipped somewhere between 15 and 20 meters, not shabby, actually.
But it was a slightly larger
earthquake, but with slightly less slip. Here's another visualization.
Japan has seismographs
everywhere, all over the country.
seismographs. It's the best instrumented place They have thousands of recording
little visualization, where in in the world for earthquakes. What I'm going to show you is a
an very exaggerated way, they'll show us the ground motion, up and down, from the earthquake
waves as time went by after the initiation. Here are the seconds down here. Let's just watch this run for a
bit here.
The earthquake starts and the waves start.
Oh, I forgot, I pushed the wrong button there.
Let's back up and start again.
The earthquake starts, waves start spreading across Japan, right?
The Tokyo region is shaking hard. 200 seconds have gone by. The network went out.
The power went out to the network in that region, so you
It's shaking the whole country don't see that anymore. It's still going.
up and down by many centimeters, 500 seconds after the earthquake
What's that, eight minutes. Is that right? occurred.
Thinking on my feet, yeah. Anyway, the ground shook all
over the country for a very long
In fact, set a record for the strongest accelerations of the It also moved the ground very hard.
ground that have ever been recorded from an earthquake.
These are a bunch of stations of
what we call strong motion instruments.
from the earthquake. They measure the largest motions
And really, the key thing to look at is down here. This is a measure of
acceleration, if you can see the
A 1g vertical acceleration would vertical axis, in units of g. One gravity, right? We're being held down by 1g.
The peak acceleration recorded be enough to throw you to where you are weightless, not quite leaving the ground.
in the earthquake at a station just up there close to the epicenter was 2.7g.
So it would throw all objects that weren't bolted to the
That's never been recorded ground thrown into the air, literally quite high.
before, 2.2g was sort of the previous record.
with motion. It did some remarkable things
It moved things so much, actually, that we could record
even seismometers. it with instruments that aren't
GPS stations that are permanently affixed to the ground are now in routine use by
geophysicists to measure these
very slow plate tectonic motions.
GPS stations in Japan. This is an example of one of the
your car. It's just a little more sophisticated antenna, and then difa lot more sophisticatedin
processing that goes into it, and it's fixed to a pier that's sunk way into the ground so it
We can measure the position with remains well fixed to the rock.
an accuracy of just a couple millimeters and update that every 30 seconds, or in fact,
every second. There are more GPS stations like
this in Japan than anywhere in the world, an order of magnitude
more than there are in
When we look at what happened in California, probably. Thousands of stations like this all over Japan.
All these dots on here, and this the earthquake, I'll show you the displacement of those GPS monuments.
is going to be a movie in just a second, are the locations of GPS
Let me call your attention to this arrow here. stations.
That's a vector. That's a scale of one meter.
So we're going to show you these
And this is half a meter. GThis one over here looks liken tnorth/south, but it's really scaled to one meter.
Did the ground go up or did it showing a vertical displacement.
go down. This one over here will show you
So let's get this guy going, if horizontaI can.lacement.
They're going.
A few will show you a noise blip for a second, that's not
And here comes the earthquake.
So you saw two things, right? You actually saw a wave go
through, and then you also see a bunch of those vectors are still
there.
What they show you, then, is that the wave was actually those
seismograph records going through the country, spreading same waves that we saw in the
there, I think the vectors still across the country. But the vectors that are still
moved and didn't go back to where it was in the first place. displacement. They are how much the ground
In fact, the maximum displacement was along the
coastline of about four meters, right, 14 feet, or so in the
up to 70 centimeters, or so. south eastward direction. The vertical displacements were
The vertical is not quite all in one direction, but they're >> Is the vmostly. all in one If you look at the view, the
coastline all went down along here, close to the epicenter. If you actually look around,
edges that actually went up. there are some places around the
You can also see that it sort of I'll talk about that. That's actually the elastic change in the crust.
at the coast. swAnd they literally look likes back here, much less than a meter, to these very large ones
they are all pointing. It's like the crust of the earth
just suddenly went "whoosh" toward the epicenter, toward the
spring loading that had been region that actually slipped in the earthquake, and relaxed that
That's the displacement of the stored up for actually it looks like over 1,000 years in that time.
uses all of that to do another earth measured by the GPS stations. Here is a version of that, that
calculation for how much the fault slipped offshore. The independent data
basically shows us the same thing as the seismic records. Go ahead. >> In a previous slide, you
showed how close Japan is to that trench. Does this mean that the Japanese
trench? >> This region, this coastline, moved four meters closer Islands are closer to that
We'll see in a second that it's not as simple as saying it got near the trench. It's actually just the release
of that built-up strain.
It'll move back from now until the next earthquake, and
We'll see it in just a second. then it will pop toward again.
see what happened. If we look at kind of a cross section through the country drawn down here, we can actually
Here is a cross section, slicing down through the earth. Here's the surface of the earth,
very schematically. Here's the top of that plate
that is going down beneath Japan, mapped to that.
What happened was, the plates are stuck together, and it
earthquakes, from the forces of that subduction, and then popped pulled the plate back while they were stuck in between the
forward during the earthquake. The coastline actually went
down while the offshore region
actually went up. The offshore up is the translation of that
30 to 50 meters offshore. That's what made the coastline
Actually, one or two things and then explain that just a little bit more. LJust one more interesting--
observation from this GPS network.
of the GPS measurements. Here are the north, east, and vertical components
That seismometer is the GPS. This is from a station by Tokyo.
and in fact, a place where the This is quite a long way away,
ground shook strongly, but didn't do a huge amount of
Look at these displacements. damage down there.
That's 50cm up, 30cm back; 40cm up, 20cm back. It's something like if you were
sitting in your chair right now,
and suddenly you were moved back three feet, forward four feet, and then
it happens six times in a row.
That's what's being shown by these GPS stations. We're calculating their global
position in every second. That's consistent with
I got an email from a colleague who was in Yokohama, just actually about only half a day the seismometers.
What he said in that email, was that from the earthquake itself, after the earthquake.
the ground was just continuously and then from the aftershocks and everything, it felt like
swaying without ever stopping, and that he knew many people
feeling motion sickness because for hours and hours, the ground had not stopped moving. who wereAll right.easick,
This is just kind of
and in fact they do. an interesting one. I said the earthquake waves spread all over the planet,
by instruments. TheWe didn't feel itled all thhere in Wisconsin.arth, and could be recorded
Science Foundation sponsored This is actually a National
special experiment going on. It's called the US Array. It's a set of individual
seismometers spaced about 40 miles apart over this whole
west coast, and they're kind of and marching it across the region. It actually started on the
of the earth. When the earthquake occurred, coall these stations that ares. Itshown on these dots recordedr
the earthquake happening. So what we're going to do,
the middle of the US, the Midwest, and we're going to isee a line move across the earthquake come across
from that station right there in, wherever that station is. I can't see very well, this record, which comes
No, we're in Colorado? is it in Nebraska?
No, we're in Kansas. Thank you very much.
All right, let's see. Let's watch this take place. I can do geography, yes I can.
So, the colors you see are up and down motions,
shown over here on the scale. I just did it again.
You'll see the color change and get brighter and darker based on just those stations I should have said that first.
The earthquake occurred, here comes what we call the P wave, going up and down.
We're going to see a wave that bounced off the primary wave that first came in from Japan.
the core of the earth. And now we're going to see
the S wave. That's the main, what we call shear wave motion across the planet.
Then we get to the surface
waves, which are the ones that have the largest amplitude
but move slower. and do the most damage there,
They're waving across, because they're coming from Japan.
the right direction, remember the great circle pathway. If you fly to Tokyo, you go right over Anchorage, right?
They're coming from the right direction.
Now, the things sort of move around for a while.
We watch those seismometers as the waves are just rippling
around the earth, bouncing off the core, doing all kinds
of crazy things.
back the other way. NThat's because they are going. The waback the other way. at us The earthquake started, andg
the waves started going around
the earth every direction, so it went right by here, but then the ones coming back
from the other side are what
The reason we don't feel them yois, you look at the scale,. >> We don't feel those? >> We don't really feel those.
that says 3 millimeters. The crust in Madison went up
and down by about a centimeter, but it's very slow. These are sped up a lot.
it goes up a centimeter and back down. Over the course of the minute,
Actually, can you feel it right now? There is not much acceleration, so we don't feel it.
( laughter ) The earthquake also excites
something in the earth
called normal modes. Those are the vibrations, or the
earth's fundamental resonant oscillation of the entire
frequencies. Have you ever seen those videos of the astronauts where they put
a little bubble or ball of water
and they blow on it, and the water goes like this
Well, the earth did that in response to this earthquake. and vibrates back and forth?
It's like the ringing of a bell, and it's still doing it today,
those normal modes are still
vibrating from this earthquake on March 11.
detectable earlier on, now I'd We can't feel them, but they're
call it just a calculation. I'm having fun with questions, but I'm going slower
than I planned to.
I do want to show you more things about the tsunami, for sure, and some other stuff.
The earthquake happened,
the waves start propagating. You saw that there are different
One called the P wave, waves that leave the earthquake.
that's the first one that goes. It goes the fastest, but it's not the biggest.
After that comes the secondary
wave, or shear wave, and then the surface waves. Those are the ones that do
most of the damage. They go slower. Japan has implemented an early
This is not a prediction of earthquakes, it's a system that once those P waves are detected, warning system for earthquakes.
computer algorithm automatically if they're big enough, a
sends out a warning to the country.
remarkably well, but this was really the first test. It turns out that this worked
This is live television, was a live television feed
from Japan. This is actually Parliament.
coming up on the screen on everyone's television ( tones chiming ) That's the earthquake warning
who was watching this. That sound.
Basically, what they're saying
Let's see if I can just make it is an ekeep going.appened ofIf I back it up,. It just did it again.
So, no human intervention, it'll keep going.
an automatically generated earthquake warning appears
that's on, and also was sent out on every television screen
as a text message to people's cell phones. They call it the reverse 9-1-1.
It sends everyone a message,
earthquake just happened, it's big enough you should take cover.
Then as we'll see, not long after this, the tsunami warning comes in. The translation
is down at the bottom.
A short time before the vibrations arrive. You can see in Parliament,
they still haven't felt it yet. >> Are they aware of it at this point?
watching TV. >> No, because they're not
They may be just getting them at this point. You'll see them start
to respond. People are looking up.
So, everybody is sort of
sitting there. Earthquakes are so frequent in Japan, that just feeling one
won't even stop people
in the middle of a sentence. The meeting will just go on,
until the event was.ow big
That's the announcer
on the television. ( man speaking Japanese ) And eventually here, they'll
break in. So they break in. ( tones chiming ) ( man speaking Japanese )
The tsunami warning has now been issued.
as an initial calculation, The earthquake was first. Now the tsunami warning,
says there is danger of a real tsunami happening.
In the interest of time, ( man speaking Japanese )
I'm going to speed this ahead a little bit-- attempt to speed it ahead a little bit.
Here we go. So, by another minute or so later, they had a tsunami warning out for this particular
portion of the coastline. And a more minor tsunami warning
The bottom line is, the earthquake warning for other regions along the coastline.
was issued several seconds before the S wave even got
to the coastline. It was a tremendous success in earthquake early warning.
thing that took place. It was basically a split second
People along the coast, even in the areas damaged badly, got somewhere between
five or 10 minutes' warning of the impending tsunami. That probably saved very, very many lives.
It looks like 27,000 people lost their lives in the tsunami,
the early warning system. The earthquake itself acts but probably several times that would have without
as an early warning. If you feel the earthquake,
especially if you are Japanese
and live on the coast, you know to move away or move to higher ground if you can.
The scale of this earthquake was
such that people were not able to escape it, or underestimated what they had to do to escape it
and that's a different story. So, the earthquake happens, the warning is issued.
but not a lot of much damage, even in the close-by regions, not that many buildings failed. The earYou probably heardamage,
that story. Earthquake engineering is good
offshore earthquakes, although in Japan. And it turns out that these
they shake the ground a lot, they don't shake it with those
that tend to really damage very high frequency vibrations
the earthquakes the worst. But the tsunami of course is another story.
And so, the tsunami arrival at
the coast was much greater inundation than was expected
But it was not much greater than had been seen in some parts over that large an area.
of this region many times in the past.
Actually relatively recently
in the past as well. I have a little bit of video
Well, this image is showing us, there is actually a seawall here of the tsunami coming in.
The harbor is out here. The water has risen, and it's thsimply risen enough that nowt up to a five-meter tsunami.
and coming over. it's overtopping the seawall
Power Point to do that. There's a great special running on National Geographic right I've got to jump out of my
"Witness to Disaster." now, you should try to catch it,
It has a lot of these clips. I'm going to use
The tsunami is arriving in a couple of the cities that got the largest inundation a litfrom the tsunami.here.
Those walls are to guard against
a five-meter high tsunami, about 18- to 20-foot high tsunami.
people have mostly moved As it came to the coastline,
into the higher regions, assuming they were safe.
other cases, they were not. I think probably people have In some cases they were, but in
mostly seen a lot of these kinds of clips.
The story was not that they were unprepared for tsunami,
but that the tsunami overwhelmed the preparation and defenses.
It gets a little shaky there. But you can see what it's doing.
Sometimes it's like a breaking wave, but other times it's just
like a rapidly rising tide
that comes up into the harbors and overwhelms the defenses.
of the water did the damage, Of course, the hydraulic power
That's a truck. I'm assuming that people saw knocked the buildings down, and so forth.
these videos on the news at the time.
But that coastline of Japan,
a lot of it's very rugged and mountainous, and there are a lot of narrow harbor towns.
There are little valleys
that meet the sea. It was difficult to get out of
inland or up-slope. That's what we just saw, the way, to get far enough
a still from a minute ago. The water is black, because it
has picked up shallow water mud along the way.
because it makes you seasick This is the city of Sendai. I'm going to skip ahead,
to watch this part. Actually, I think we've probably watched enough of this stuff.
They are on YouTube, exactly. Watch the National Geographic special if you get a chance.
Let's wake up Power Point. It's really good.
Let's talk about the tsunami generation. I showed you my stick and how
it pops forward, and I said it's the displacement of the sea floor. Let's make sure we have a grasp
of what's going on offshore to make that happen.
Here are the two plates merging, the stickiness pulling that
plate back, and then it's the pushing up of the sea floor that pushes all the water above it now, so the water
suddenly has a many meters bulge
water will spread out as a wave. in it, set up over just a few seconds or tens of seconds. Water can't make a bulge,
Water wants to be at sea level. That's the source of the tsunami.
The source of the tsunami is the displacement of the sea floor upward by the
as it moves. unsticking of that upper plate
Here's the same thing, if that was confusing.
plate is stuck, it bends back, In a diagram, the subducting
and that distortion, that elastic distortion just like with my stick
pulls the offshore part down, but moves the on shore part up. For the hundreds of years between earthquakes, the land
has been slowly rising
it launches the tsunami and also out of the sea. And then during the earthquake, it suddenly pops forward,
caused the coastline to drop down by that 70 centimeters.
in Indonesia in 2004, and the coast of Chile last year. So the tsunami is this sort of That's what happened
version bulge here. There is the nearby tsunami, obviously exaggerated cartoon
The nearby tsunami, again, and the far traveled one. Let's look at those.
There are observations of bigger was one for the record books, but maybe not quite as much as you might think.
tsunamis that have happened on the planet. This region in Japan though,
the same coastline, just
recently, this was just posted online by the Earthquake
days ago, has gone out and done initial surveys of how far Research Institute about two
height was just a few meters, two to four meters, or so, the water came in offshore. In the open ocean, the tsunami
in the open ocean. That's where the water is deep.
Just like any wave, as it comes in to shallow water, the
that are like funnels, wave slows down and piles up. When it comes into the harbors
it piles up more and more. The maximum-- This is hard to read, I realize,
but these are meters over here, observations from 2011. The maximum measured value
More than 35, close to 40 meters is somewhere close--
of water height during the tsunami in one of those towns.
that the water rose during that tsunami. That is 125 or 130 feet
and then actually cover it That is, you know, it would cover my building, Weeks Hall,
twice over if the tsunami came in of that elevation. We'll come back to the rest of
what's on that in a few minutes.
Actually, no, I put it in here. Let's talk about this right now. It turns out that you could say
was the tsunami unprecedented?
Tokyo is to the south somewhere. And the answer is, along this northern coast, this is north of Sendai.
This was not unprecedented. In fact, it's happened twice in the past 120 years, or so,
in very similar scales. This is a view from kind of looking towards the south.
but there's that same coastline shown over here. I know it's a little confusing,
Hokkaido is here and now Tokyo is over there.
These are the heights of
tsunamis recorded in 1933, from a smaller earthquake that
but up to 23 meters then. In 1896, the same coastline, just affected this coastline,
So similar magnitude, well-known to occur. same little villages and towns, up to 38 meters at that time.
to match these kinds of scales. The business about the nuclear They built the tsunami walls, but they really never built them
It turns out this region south reactor, that's down here along this part of the coast.
it looks like, about 1100 years, of the city of Sendai has not experienced a tsunami of this kind of scale in,
over 1,000 years. But they had experienced tsunami before, and there was certainly
not any lack of understanding that tsunami could hit
Let's talk about the that coastline, including where the power plant is.
You probably saw the news fathat day, and saw that. I don't want to overrun my time by too much.
they were saying a tsunami is coming towards Hawaii, and
going to arrive at such and such
a time, and hours from now. Let's look at what happens when a tsunami travels
across the ocean. This is actually another early
warning detection success story. All around the Pacific Ocean,
there are a number of these buoyed stations called the
DART system. What they are is, there's
a sensor on the sea bed,
in the water very precisely. and it's basically just got a pressure gauge in it. It measures the pressure
So, when the water height, or a column of water
So you can see the tidal signal over several days in this DART station, that's what the blue line going up and down
is over here, and that's just the tide going up and down
out in the open ocean. This station was several hundred
miles offshore near Japan.
But when the sudden spike in the water height comes in, they know
different. that's got to be something
In fact, that's the tsunami arriving at that station several hundred miles offshore.
That triggered a warning. I should say the earthquake triggered a warning to the
in Hawaii. Pacific Tsunami Warning Center
by that earthquake, and that These DART stations were then used to detect that a tsunami had in fact actually been made
the warning had to go out. What that does actually, is feed into a computer model
immediately, within about an
hour after the earthquake, this he computer simulation was done by NOAA, and they show
the earthquake occurring, this down here is the record
at some of the nearby stations that are these little squares
up here, and now the tsunami
is spreading across the Pacific Ocean. It turns out the wave travels
at a speed that's determined
solely by water depth. It's just like a shallow wave tank experiment in a physics
class, so you can predict what
time it will get to Hawaii and what time to
with a lot of accuracy. I you know a little about the size of the tsunami initially, the west coast of the US
They did a great job. They actually predicted the size you can predict the size.
Crescent City, California, in Hawaii spot-on, and the time spot-on, as well as warning
If we look at a version of that Sthat just shows the predictedr wave height from the simulation around the ocean, it shows
up to just 240 centimeters, like I said, just a couple
You can kind of see that it doesn't spread evenly. of meters in the ocean, spreading across the Pacific.
That's because water depth varies around the Pacific.
It's not one constant depth,
it varies a lot. You can see that it sort of aimed the far distance waves
out to the open ocean,
wave height, you know, hit Hawaii over here. There's this interesting finger that looks like a kind of
concentration headed straight for the coast of California. It turns out that's actually
a sea bed feature, called the Mendocino Fracture Zone.
It's a shallow water feature that extends across
the ocean floor, and acted as a wave guide for the tsunami, carrying it in that direction,
right there of the tsunami, where it did more damage than anywhere else, north and south and causing a larger magnitude
Damage happened in Hawaii. along the coast.
The news sort of overwhelmed this story, but actually, there was a lot of economic damage,
I don't think anybody lost their
lives in Hawaii, along the Kona coast, if you've ever been there on vacation, a bunch of those
hotels had water wash right through the first floor.
Okay, a little bit of historical perspective on earthquakes.
We have heard the story that, you know, the tsunami or the earthquake took us by surprise at some level,
and that's partly true
and partly not true. There is the map of some of the earthquake and aftershocks.
Here are the ruptured areas of known previous earthquakes in the 20th century,
These are all areas that are give or take a little bit.
magnitude 7-ish earthquakes. Remember, the magnitude scale is a logarithmic scale, so a 9
is 100 times larger than a 7, actually in energy released it's 300 times larger.
have happened frequently. The year is shown for each But so magnitude 7 earthquakes
generated the tsunami I just of those. Two of those are the ones that
showed you the records of. What had never happened, though,
was an earthquake that spanned in historical records
this whole region. Northern area had had tsunamis, southern area hadn't really had
tsunamis. But it turns out that that
record is just not long enough to capture all the events.
The region down here is called
be able to point right to it. It's somewhere in this region Sendai right here.re, and thThe Sendai Plain had notd
experienced a very large tsunami
in recent historical time, but this tsunami washed up to six or seven kilometers inland
along that low elevation region.
Of course, that's where a lot of the damage and loss of life happened.
It turns out that 10 years ago, a paper was published by clever tsunami experts that
before, and it happened before showed that this had happened
about in the year 869. It was known there was a large
time, from historical accounts, and it was known that a tsunami had come inland. earthquake in Japan at that
we didn't know much about. But the size, you know,
not good enough to completely Hiestimate the magnitude.an arWhat the folks did though,e best in the world, but they're
and maybe this map doesn't show it very well, but here's the was they go on land,
coastline. They go on land along
a transect and dig trenches or holes down into the ground.
In the upper few meters of the soil, they found these sandy
marine sand deposits. Those deposits are
records, sort of, of a tsunami. It turns out that they could paleo-tsunami deposits. They're the archaeological
correlate the sheets of sand from different trenches at
different distances on shore, and then they used things like
radio carbon to date the ages, roughly speaking.
There are some error bars on those, but at any rate,
the tsunami had traveled inland by about the same distance, thof four to six kilometers,e that 1100 years ago, or in 869,
happened twice before that over the span of 3,000 years or so. and furthermore, that it had
So, approximately once every 1,000 years, instead of
a magnitude 7, this region seems
to have a magnitude 9 scale. I left part of the story out, but they basically model
the source of the tsunami back from what they measure in the trenches on land.
pre-historical records So this is real sleuthing out
of tsunamis. The picture we're left with is that we can have smaller
events that we thought were the biggest that region had,
but every once in a while, the whole thing sort of unzips
in one big event that covers
the zone of several of those smaller ones. This is actually from the paper.
More than 1100 years have passed
since that Jorgan tsunami and the possibility of a large tsunami striking
the Sendai Plain is high. They estimated, actually, they were conservative
But what they wrote down and underestimated the scale.
and actually told the people who run TEPCO several years ago,
was at risk of a large tsunami was that their nuclear plant
inundating the plant, to much larger than the protective walls could cover.
The story of why that didn't
happen is a political one, not a scientific one. Let's see, I think what I want
to do is just bring up a couple more things.
The scale of the earthquake, I want to put in perspective
for you a little more.
kind use to illustrate the I talked about it at the beginning. Here's a little chart that we
magnitude scale for earthquakes running from below 1, again, it's an algorithmic scale,
up to the largest earthquake
that's ever been recorded, which was 1960, off Chile,
at magnitude 9.5. You know, they're very rare. another subduction zone,
Then there are 20 or more magnitude 7s around the world Once every single, year,ntury year in and year out.
You don't always hear about them
if they don't do a lot of damage.
of magnitude 5s, There are thousands
and there are millions of magnitude 2s that happen every year around the planet.
The earthquake that just happened, and the Sumatra
earthquake, were almost the same size.
They fall right up here along with the biggest ones that we have a record of. Notice the energy equivalent
scale.
Here's a lightning bolt, or the Oklahoma City bomb This is a bit of an old map.
The Hiroshima atomic bomb released the energy equivalent
to the slip on a magnitude 5.5 earthquake.
The largest nuclear test
was close to an 8. These are way above there, and
that happens on the planet. Here's another way of actually above any other man-made event
like this one are so important looking at earthquakes, and why subduction zone earthquakes
relative to other earthquakes. This is a pie chart of the energy released by all
the earthquakes on the planet from 1906 to 2011.
So a century of earthquakes, everything we've ever recorded.
Well, all the ones less than
from 6 to 7 are that piece magnitude 6 are just that piece of the pie. All the ones from magnitude
of the pie. All the ones for magnitude 8 to 7 are that piece of the pie.
Chile in 1960, plus Alaska in 1964, plus Sumatra in 2004, plus Japan just now,
all the earthquakes in the whole is half of all the energy
planet have released in a century, just for earthquakes. Here's another way of seeing the
same thing. We call it the cumulative moment release, maybe it's
but it's the same thing through time. Earthquakes happen, they a kind of technical slide,
and then boom, in come -- There was one in 1952 that was pretty big, 8.7 or 8. pop off, they release energy,
and then Alaska, then Sumatra and Japan, with these periods where not much happened And Chilein between.gest one,
Another way of looking at that, here is just the earthquakes
bigger than magnitude 8.8, since 1900.
Well, we say, and we have said
according to that statistical fochart I just showed you,e to questions that earthquakes happen at different sizes
and they happen at random times. They happen randomly in time.
But all the magnitude 8.8 and larger earthquakes that we
know about, that we have records for, basically happened either
in a cluster between
1952 and 1964, or in a cluster that maybe we are right in
we don't know, since 2004. the middle of, at the end of,
That's the Indian Ocean. That's Chile last year. That's the one
that just happened. And so, there is at least a hypothesis, just a hypothesis,
actually these are like global among seismologists that
trigger or global aftershock sequences, that when one
it shakes things up enough really big one happens,
in other parts of the world that perhaps ones that are ready to go statistically pop off
more frequently.
This isn't a very long historical record.
years like this, we might be able to say whether Basically, when we have 1,000
that's really true or not. But it certainly looks like
that's possible.
You can conceive of the physics. That's a controversial
There are lots of people from the US Geological Survey statement.
totally unrelated to each other, on television in the past month who said these earthquakes are
it's a coincidence. I also don't necessarily believe that this has happened. I don't necessarily believe
But it's an interesting observation that that's it they are related to each other. We don't really know.
to a fundamental question, for magnitude greater than 8.8. So that's kind of the answer
are all the recent earthquakes related to each other?
just no, except for aftershocks. For a long time, the answer was
Two things that have happened Jusin the last decade or two,en fault, yes, we knew they were related.
nearby, the change in stress suggest that within a given region of the earth, even
when one earthquake occurs can kind of set off things
You know, if you pop one nail out of a board, it might make the next nail likely to pop, in the adjacent region.
and so on. and the next likely to pop,
Now we don't really know the answer to long distances. Probably mostly no, but for
these very largest events people are starting to ask
those questions. I'm going to end with a question
that people always want to know about earthquake prediction.
In terms of a useful prediction, And actually, the answer is really easy.
something we could give you a warning that in the next three days,
or in the next two hours, or in the next month there's
of the San Andreas fault, or this part of the Japan coast, going to be an earthquake of magnitude 7.5 on this part
no way, can't do it. We have not found anything
that holds up.
There's lots of tantalizing things that happen for one earthquake, when we look back,
like those foreshocks, but when you look at them globally,
no matter what you hear on the news. we just haven't got anything. We really don't have anything.
that it's impossible So, we don't have it. And in fact, some people argue
from basic physics, and other people think we just haven't measured the right thing.
I'm actually in the second camp,
that we have not measured the right thing. That's a different story.
Long-term forecasting though, is sort of like long-term weather forecasting.
estimates based on past events. We know where the plate boundaries are, so we know Yeah, we can make probability
to have big earthquakes, which places might be likely
and we issue risk factors. Those take a form like this,
a certain intensity of earthquake. 30-year probability of exceeding
We have one like it in the US. This is the official Japanese government's warning document.
They really predicted a very high chance of earthquakes
I'm working in, because of that in part, not the only reason down here in the region that
we're working there, actually, not at all.
This is one of the lowest probabilities that was mapped for Japan, where that earthquake
So, is it humbling just occurred.
for seismologists? You bet it is.
told you about why we really There's actually more I haven't
thought this region wasn't even capable of a magnitude 9.
that we were wrong about that. It just proved to us
Okay, so that's the stuff I talked about earlier on. I don't have a slide like this
for Japan.
The Japan earthquake was smaller, probably closer
But the region of the Sumatra earthquake compared to the to this area.
Pacific Northwest is about the same, and the same size
earthquake can certainly happen up there, so they are putting tsunami warning signs all along the coastline.
If you go to the coast of Oregon, you will see the signs
Thanks a lot. I appreciate your patience all over the place, and you should pay attention to them.
and I( applauseo answer more questions.
)