This is geology, B. I'm all of us, trampled, unless
you live in a place like Japan or California, most of us have
never experienced an earthquake, but we certainly hear about them
regularly, especially when the damage they reek is newsworthy
this podcast. Focuses on earthquakes, the
geological faults on which they occur, and their impact on
humans. James Jackson is Professor of
active tectonics at Cambridge University and an expert on the
geological processes including earthquakes that are shaping our
continents today. James Jackson, welcome to
geology B, what's going on geological speaking.
When an earthquake strikes, this week happens when rocks break
and slide past each other on surfaces called, folks.
They could think of a knife cut in the earth and the rocks are
sliding past each other on. At knife, cut.
Now normally it's held together by friction and you have to
overcome that friction. So imagine you have a brick on a
table and you push the brick. You have to push a certain
amount before it actually jumps forward and that's what's
happening in. The earthquake is friction which
is an overcome and it's the shaking as the Rocks grind past
each other, doing that movement, which causes the damage, the
earthquake people feel and is the shaking.
But the cause of it, is this breaking of rocks on false So do
we know where all these Faults Are what we look like cotton
under that, because what happens is that, they move again and
again, in earthquakes, the same fault, will move again and again
it only moves a few meters even in the biggest earthquakes, but
given the huge time we have on Earth, after thousands of these
earthquakes, you actually make the landscape.
So the landscape is often a clue to where The Faults Are and so
reading the landscape is a bit like learning to read at new
alphabet when you book once you speak, The language, you have a
head start and where these things are.
Does that mean that if there are faults away from landscape
features? We don't know where they are.
Well, most of the folks have some effect in the landscape.
So the folks can either move up and down or sideways moving up
and down, makes mountains, or it makes basins and lakes,
depending, which side of the fault you are.
And so that's a help and places where this is going on the other
folks move sideways. As they do an example, the San
Andreas Fault in California, They still end up as features in
the landscape because as the Rocks grind past each other and
folks who get broken up and they get the easily eroded by streams
and rivers and so on. So, they quite often make linear
values, or Scott's or features in the landscape, which are
quite often visible from the air, for example, in are
photographs or Satellite photographs and they're often
followed by roads and rail hissing.
So, people exploit these things also So when an earthquake
strikes, how much movement might occur across a fault?
Well, that is basically what determines the size of the
earthquake, or the magnitude or the Richter magnitude has been
straight As refer to it. But even in the really ready,
biggest earthquakes, the movement is 1020 meters of
biggest. We know, of, in modern times was
the one in Japan in 2011, which moved 50 meters which was
extraordinary, but that really was unusual.
Most the small earthquakes will move just a few millimeters or
so. Two meters.
So that's really what determines the size of the earthquake.
So thank you Nate earthquake. You're talking about maybe 10
meters or more slip a magnitude 5 earthquake.
You're talking about a centimeter or a few centimeters.
That's really what determines the size of the earthquake.
And how could we measure this slip?
Well, there are various ways of doing it.
Sometimes it breaks the surface, and you can just see it because
actually, the magnitude also determines how long the
faulting. So the great earthquake in
smarter in 2004 which produce sucks Me for example, was 1,200
kilometers long. That's from here, where I'm
speaking Cambridge London to Rome, right?
That's a great length and it, moved 20 meters or so huge
amount. So, that kind of thing is easy
to spot. The smaller ones are often
underground. A don't have any motion visible
at the surface at all, but we have very sophisticated ways of
seeing what's going on. We can tell from the sound or
shaking that the earthquakes, generate how much that there's
been. That's the science of
seismology. We can see How much the ground
surface roundabout moves by looking from space with radar
images, or Optical images? And we also now use GPS to do
the same thing, GPS is the technology that is used for your
sat-nav, a, from the car, for example, which if you process it
carefully enough, will show you how things move to within a few
millimeters. You don't need that accuracy for
your car, but we can do it when we use it for our purposes.
So did we do that? For example, for the big T 11
earthquake in Japan? Yes, you do.
Because actually and this is quite interesting, the analogy I
gave you a pushing a brick across the surface of the table
isn't quite right. Imagine you had a sponge and you
push the sponge across the surface.
The sponge will actually compress quite a bit before it
suddenly jerked forward. And that's what happens to the
Rocks. So you can see the Rocks
actually bending and bulging before earthquakes and you can
see after earthquakes how they relax again and they change
shape. So after The great Japan
earthquake in 2011, the whole of Japan on that and stretched, it
relaxed about 3 meters. So Japan was 3 meters wider
after the earthquake and it was before and do we measure that by
having GPS sensors on each Coast?
Well changing. So, in fact, there are hundreds
or thousands of GPS sites measuring all the time because
ditions in places like Japan and that's increasingly throughout
the world. And part of the reason is to
monitor earthquakes. And so on these sites will tell
Where they are relative to each other through within a few
millimeters. So they move several meters,
that's very, very easy to spot. But actually, to be honest, the
main reason they're being installed everywhere around the
world is this is now how you define property boundaries on
maps, you no longer say the boundary of my house is where
that tree is or where this river is, you just give it a latitude
and longitude from the GPS and that's the basis now of modern
surveying. So that's why that is now
rapidly expanding as a resource. The other thing you can do, this
is another Modern trick, which is very interesting.
You can do this with radar images, from space or Optical
images from space. Is you take a photograph of a
large area and you divide it up into little pixels, little
patches on the ground, maybe 50 centimeters across and then you
take another picture after the earthquake.
And in the region where the fault is.
These pixels have moved around on the edges of your picture.
If they haven't moved around. So, you simply superimpose one
on the other and round, the edges of your picture.
The pixels have moved, they all overlap.
Perfectly. And we're the folks is they've
all moved slightly and you can measure how much they've moved
in this will again give you the movement of the ground within a
few centimeters. It's not as accurate as GPS, but
you cover a much wider area, instead of just a single point
and these things are very powerful when they're all used
together. So if you use seismology and the
space Imaging and the GPS all at the same time, you really can
nail what happens in extraordinary detail which we
could only have dreamt about 20 years ago.
That's amazing. So So, with these satellite
image Maps, can we but of actually see this building
moved. So many meters over that way and
river move that way. Yes, indeed.
You can easily and actually, this is a bit of a pain in the
neck for land, surveys in countries like New Zealand.
Their National Grid is moving around all the time, it has to,
it has to change with time because because this is
happening throughout the country and the same is true in Japan.
The downside of measuring things to Within A millimeter is that
they are moving within a few millimeters a year.
Most of these, are they Any of you.
So although most of the earthquakes we hear about happen
in areas that we know high risk, like, you mentioned Sumatra in
Japan and I suppose that apply to the whole Western rim of the
Pacific, as well as places, like, California earthquakes
actually, do also happen elsewhere, but much less often.
Why is that? Yes, this is an interesting
feature of our modern Earth today is that the really, really
big earthquakes happen around the rim of the oceans and the
Pacific and in place. Is like Indonesia, but that is
not actually where most people die.
In earthquakes, many more people die in earthquakes in the middle
of continents and particularly in Asia.
So the Great Earthquake felt for Trans all the way through the
Mediterranean, the Middle East and into Asia, all the way to
China through places like North India, Tibet and Central Asia
that area which is a huge, huge area as small earthquakes, but
they kill many more people. And there are multiple reasons
for that but the reason why it's so different is Because the
continents behave in a different way, from the oceans, the oceans
are really the story of plate tectonics which everybody learns
about now even in primary school that the Earth is split up into
these spherical caps which move around relative to each other
and the earthquakes happen, where these caps interact with
each other and round, the edges of the oceans places like Japan,
South America, Central America, or Alaska.
For example. What happens is the ocean slides
underneath the adjacent continent?
Rather like a conveyor belt. Imagine the conveyor belt or
escalator on the staircase, going back into the ground.
That's what's happening to the ocean as it slides on the
continent and that interface where we ocean slides under the
continent, that's where the earthquakes happen.
So there's essentially one fault, which is doing the job
and it has to move pretty often because it's moving quite fast.
Typically a few centimeters per year.
Now, the continents are all the different because the continents
are not really part of that story.
The continents are like, Floating on these plates.
They like passengers. And they don't cause any
trouble. If they're just an island in the
middle of the Pacific or something, you get a problem
where one continent bashes into another continent.
And this is the problem with India, for example, which
belongs adjacent to Madagascar and Antarctica and Australia in
the Southern Ocean, it broke away and crossed as an island in
the Indian Ocean until it bashed into Asia.
And when you have a situation because the continents are made
of different material from the ocean, it's much less dense the
confidence that I life jacket. So they simply won't go down
there. I go down the hole like the
escalator or the conveyor belt and they just bash into the next
continent and the whole thing crunches up.
And so what's happened in the case of India is India, has
smashed up Asia all the way from the edge of the Himalayas to
Mongolia which is 3,000 kilometers further.
North, the whole place is smashed up.
So there are many, many earthquakes are of a much wider
region instead of essentially being a single big fault on big
earthquake, Do you have around the edges of the oceans?
So what happens over millions and millions of years?
As movement happens repeatedly over either a single fault as
you mentioned at the plate boundaries or this massive
network of faults that you may have in the interior of a
continent. Well, what happened to India,
collided with a sure about 50 million years ago and it's going
at about 4 centimeters per year. It's not like a car crash, it's
not stopped, it's still plowing into Asia that rate for He's
here about the rate, your fingernails grow and over 50
million years, then India has plowed 2000 km into Asian crush
it up. And that's why there are
hundreds and thousands even of faults in that part of Central
Asia. And because each of them is
contributing to that job of allowing India to move north,
eat particular, one doesn't have to move very often whereas The
Faults offshore Japan or South America.
For example, they have to do all the work, they're moving
frequently because they have to do all the work.
Does anybody want V to do it? So words earthquake to repeat
every few tens or maybe a hundred years or so in Japan and
South America, in Central Asia, where there thousands of faults,
each fault, may only repeat its movements.
Every few thousand years often Way Beyond human memory or
recorded history. And so they tend to catch
people. Unawares.
People are unaware that they're living in a dangerous place
because there are earthquakes all over the place.
There's nothing particularly distinguishes where they are.
Let's come down to the Fatal Attraction between cities and
earthquakes. Why do we build cities in areas
that are prone to earthquakes? Yeah, this is an interesting
feature again of Central Asia, really?
Or this great Alpine Himalayan earthquake belt from the
Mediterranean to China is that earthquakes occur and seemed
quite often to Target places where people live and you think
it's just as bad luck or is this the kind of being vindictive?
And the reason for that is that the earthquakes and the faults.
Responsible for making the mountains and the particular
responsible for the edges of the mountains where the mountains
meet deserts or high plateaus like to bed.
And that's where people live. If you like living on the edges
of mountains, because that's where the water supply is, its,
where agriculture is possible. It's usually where the trade
route runs on the edge of the mountains and of course it's
strategically important for access to those trade routes as
well. So what happens is that
settlements grow up along those trade routes on the edges of
Mountains and then they develop, and they become bigger and
bigger. And so, the populations
concentrate in these dangerous places, it would be fine to live
in the middle of the flat desert in Iran or Central Asia, but
there is no likelihood there. There's no Waters and
agriculture possible. You can't live there.
And so you live with where life is possible in these desert
countries and that is almost inevitably places where life is
possible because the faulting has created the circumstances
that make agriculture and water supply possible.
So, You've described how that can happen at the edge of
mountain ranges such as the Himalayas or the Alps where you
have well in the Himalayan case India plowing into Asia.
Does that also apply on coastlines?
Because we love to build cities on coastlines in places where
the earthquakes. Yes, is tectonic plates that
just crunched together. They can also pull apart and
drift apart, and that's for example, why the coastline is
where it is between Greece and Turkey or between Norway and
Scotland. Although Annoying Scotland is no
longer active. It did it all about 100 million
years ago, but now it's active in places like Greece, Central
Central Aegean, Sea of Japan, Greece, and Turkey, and indeed,
that is why the coastline is where it is.
That's where most of the action is, that's where the earthquakes
are. And so, if you live in countries
where there are earthquakes, it's a good idea to ask why is
landscape? Like it does.
And that's nearly always because of faulting associated with
earthquakes in places like California or the Mediterranean
Middle, East Central Asia. Zeeland East Africa, the
mountains are there because of the activity and faults in
earthquake. So what impact have earthquakes
had over history on these cities that have succumbed to this
attraction to earthquakes well. So this is very interesting that
the number of modern cities which have grown into a huge
population, centers along, for example, the old Silk routes,
which connected China, to the Mediterranean, a lot of cities,
along those routes have been destroyed, Multiple times in the
past, but in the past, they were intended to be rather small,
they tended to be stopovers on trade routes but now there are
any of them even capital cities of countries in Central Asia and
they've been destroyed in the past, but whereas, in the past
say, they're unlucky, they lost 10,000 people or so now they
have cities of million or more and they're very much more
vulnerable. It's still in the dangerous
place but they've increased the population dramatically without
I'm sorry to say in most cases. Their resilience to the
earthquakes that are bound to happen again.
Can we help people in these cities, prepare for the next
earthquake, by predicting when it'll happen or roughly when
it'll happen, for example, I know that we can detect bulging
movement on volcanoes that for warn us of eruptions on
volcanoes. Does that also apply on the
tectonic scale? Two continents.
Well, now you've touched a very interesting question and we have
to be careful how we use words in this area.
Short term prediction means saying, there's going to be an
earthquake sometime within. You know, say let's say next
Wednesday, plus or minus of a and in some particular place
such and such a size and we can't do that the science isn't
there, people have looked very hard for precursors.
They're called with some sort of Warning Sign beforehand.
There's nothing which has been found to be reliable and it's
not something which has been successful.
We contrast that with Forecasting, long-term
forecasting is fine. Long-term forecast is simply
saying where there's been an earthquake in the past few days
about it will happen again in the future sometime.
You can't say when but we can say quite a lot with a bit of
work, about how big that earthquake will be, what its
characteristics will be, how much the likely shaking will be
along last, how big it will be, how much the default might move.
But all these things are of interest to Architects and
engineers and planners because if they know what the threat is,
what they're up against, they can actually design things for
it and that's It's been very successful again in countries
around the Pacific Rim. For example, it's much harder to
do in Central Asia because there are more faults most that we
don't know about and there are generally other priorities and
this is the problem is that in many cities in places where
earthquakes are less frequent, but more dangerous in those
places people have other priorities.
So if I was to say to you that the last earthquake was 500
years ago in your city, you would say.
Well everyday, I takes me two hours to get to work.
As congestion, the air quality is rubbish.
Our problems of water supply traffic Thomas on this
earthquake, 500 years ago, that's not my problem, but
actually, it is your problem eventually, but it's not highly
prioritized by contrast. If you lived in, in Chile, for
example, you feel earthquakes all the time, and, you know,
that you'll feel 95. Earthquake every year.
You'll feel 97 probably every ten years and they'll probably
be a magnitude 8 earthquake in your lifetime.
You know, this is not a theoretical threat, it will
affect you, your Children and your grandchildren and people
are quite happy to prioritize it.
And so in fact they're helped around the Pacific Rim by having
many many more earthquakes in the same place repeating as it
were and in Central Asia where they're more distributed and
less frequent in any one particular place and so we can
help them. They need to do the work to put
in the work to know what the hazard is that they're actually
facing. There's no real shortcut to that
but it's just on the whole not. Sighs places like Japan, New
Zealand, California and Chile have put in decades of really
hard, scientific effort to find out what they're up against so
they can plan and prepare and they've been super be successful
at it. When you say what they're up
against, does that mean mapping the faults in detail?
So we have a better idea to east of where the next one might be
that's going to rupture the. Yes certainly that's part of it.
But there are two things which could send a few or an engineer
building a dam. For example, in a River Gorge,
you want to know why that Gorge is there and if the gorge is
there because there's a fault, the rivers flowing down it that
affect how you build your down, which I get physically ripped
apart. So there's an interest in
knowing where the fault itself is for sure, for particular
facilities and threats. But also, in many places for
planning purposes, statistics are good enough.
You just want to know in this particular area, what is the
largest likely ground shaking the duration, one of the First,
you select shaking in order to allow people to plan how to
build buildings and so on. So there's a difference between
being physically ripped apart by being astride the fault and
being shaken. Because your next to the fold,
how good are the historical records?
Speaking of knowing what the impact is being in history in
these high-risk areas and ironically, the risk areas which
are certainly in Central Asia and the Alpine.
Himalayan Central Asia region their historical record is much
better than around the Pacific Rim so that the historical
record in the right places at least between the Mediterranean
and China go back 2,000 years or so.
Whereas around the Pacific Rim, they've been inhabited by people
writing records or keeping records for not very long, a few
hundred years except for Japan but in Asia there's an enormous
amount of information in the records of Empires.
So the Byzantine Empire, the Ottoman Empire, the various
Persian Empires and of course China were quite bureaucratic.
They kept very good records of these things which Be an
enormous goal by now. People go back and look at these
counts kept by the bureaucracies of those time.
It's a very, very scholarly activity.
You have to be a fantastic linguist and historian just to
get to first base, might be able to look at in this stuff and
then you have to know we talked about in terms of the geology.
The seismology engineering to know how to interpret.
These records are very often exaggerated.
They have particular styles of describing these calamities and
they're not interested in things like ground motion, their
interests Add in disruption to life and property and trade and
so on. But you can interpret these
things and they are extremely helpful.
You have to get at that sort of information in these other
countries should be settled this or for less Long in a more
forensic. Detective kind of way by looking
at the geological evidence, which is also possible that hard
work, that's fascinating that work that needs to be done is
both very much historical and sociological and really human in
nature. Going back these thousands of
years as I was on the other end very cutting-edge measuring
precisely where Faults Are and using all the battery of
techniques that we have today to figure out the present
situation. It's very interesting it and
there's a very good relationship between these routes.
The historical work. Is an immense.
Long-term work of scholarship is not the sort of thing.
You achieve in a three-year research around it.
Something we know people spend their life time, researching the
history of earthquakes in Clash or something like that, and they
come up with these historical earthquakes and then it It's the
job of the modern scientists to then figure out.
Okay, where was The Fault? Which was responsible for that
earthquake? Can we actually find on the
ground? What did it and the evidence
that it really did do it for the whole thing together.
So, there's a very close working relationship between these
different groups. So, you live in Cambridge near
London and I live in Boston. Are we in a safe area for my
historical earthquake point of view in the sense that most of
the earthquakes in the United States on the West Coast?
And most of the earthquakes in Europe, by the Mediterranean
heading Eastward, through Italy, Italy, Greece, and Turkey and so
on, it doesn't mean we don't have any, we have some and lost
of confidence have smaller earthquakes.
We have any from in Cambridge. I remember from the last ten
years, the couple of earthquakes, which are working
people up there. It's very, very small by the
standards of these proper earthquake countries.
Could something people wouldn't get out of bed for, but they're
not negligible, you have to watch out slightly.
So for example, if you're building something which is very
sensitive, like a nuclear power station, you really need to know
what's going on. So you will have some assessment
of what you think. The likely largest historical if
B was or might be in the future and you will over designed to be
safe in that. And so although people in
England really don't think about it, breaks the electricity
generating board who run the new capacitation, certainly do.
And they've designed to in order to be conservative for what they
think is the largest historical earthquakes.
And the same is true, for example, needs Coast United
States. And that's more interesting.
Because actually you probably know that the Atlantic opens in
the Jurassic 150 million years ago something and of course, the
Appalachians is part of Scotland, essentially belonged
up against Ireland and Scotland and you think it's just the
other half of that situation in the North Sea.
Now, in the UK and Northern Europe, we have of a long
historical record mainly based on monastic record monastic
Chronicles, which go back. Nearly two thousand years and
there really has never been a really big earthquake in the UK
and the We'll see in those last two thousand years, nothing
awesome about Matthew 5 and a half which is really not going
to cause trouble and you go to United States.
The same is not true. It's been settled for a few
hundred years at least a good historical record for the last
few hundred years. And in that time, they've been
several earthquakes quite a lot, bigger than anything in Europe
in the last 2,000 years, and most famous was in Charleston.
South Carolina in 1886, there's one in caveman, which is where
you never be in Massachusetts. I think that was about 1750
Five, but these were Manchu 6, Plus, and certainly bigger than
anywhere in Northwest Europe, know why there should be that
contrast between geologically. What if you like two halves of
the same mirror, like the lad. You just broke split.
The two in part. Why the American side should
behave? So differently from the European
side. No one really understands, but
they do. And so you have to design for
certainly big earthquakes and people are contemplating in
Northwest Europe. Charleston earthquake did a lot
of damage in South Carolina in 1880.
See, it was a big deal and I just very well investigated and
they were written up and there's a lot of detail about it.
Didn't do too much because of course in those days in South
Carolina, people mostly lived in wooden houses which were quite
well built, they behave very well.
Where does the best building material can happen in office?
Europe would is an expensive building material so it's not
that common. I'm going to ask you for my last
question to be a little bit of forecaster, I know you do.
Like to do that. But what I'm wondering is that
even though the earthquakes that have happened in these dangerous
belts in Central Asia and elsewhere are on time scales
longer than an individual human life.
So, there isn't a personal memory that perhaps makes people
aware and attuned to the risk. One thing that has happened on a
shorter time scale is this enormous growth in our
scientific knowledge understanding which you've
alluded to, in this talk? Do you have a sense as to
whether this knowledge can be brought to bear to make this
connection between cities and false, a little less fatal in
the next few years, and decades while development proceeds in
these countries, I hope so. That is an excellent question
and that has occupied me the last 10 years.
How do you actually turn the scientific knowledge into some
increased Public Safety, and it's presumptuous to think the
problem is just scientific. Of course, it's not it's to do
with well. Health and Social logical
conditions, cultural conditions, economics.
All those kinds of things as well in the long run.
You know, the only thing which works is education.
People need to know what they're up against a need to know, it's
not hopeless, right? That the great iniquity, I think
is short-term earthquake prediction, which is like
promise of a Panacea, a silver bullet if you allow the public
to believe in it, it also allows them to think it's not their
problem, a scientist will sort it out one day, they'll say the
earthquakes can be Wednesday at 9:30.
We I didn't have to do anything. That is faithful that kills lots
of people that attitude and that's one of the roles of the
scientists is to say, actually, that isn't going to happen.
On the other hand, there are things you can do to make life
safer big a on. There are lots of very switched
on good people in those areas governments and ngos and Civic
leaders who want to do the right thing and who care about this
and they need help but the scientists can help them by
helping them be realistic about what the public.
He's going to face and they're in the number of such studies in
countries like China and Nepal where you do a detailed study.
You know this was our son incidentally in Kathmandu which
had the big earthquake in 2015 before that earthquake and NGO
had put together a study of what would happen if the previous
earthquake which was 1934 in Katmandu repeated, right?
And what would happen if that 1934 earthquake repeated today,
given the so change in circumstances in terms of
Greater population population density, the quality of
buildings. The lifelines by which they mean
things like roads and water supply and power Appliance on
what would happen today and they did that study and it wasn't
some arm wavy publicity stunt. It was two years of really hard,
scientific evaluation of what that earthquake was in, 1934,
what caused it, where the fault was that moved?
What was the ground shaking? What would that ground-shaking
do today? And they publish it as a story,
almost as a cartoon picture book illustrating the consequences of
such an earthquake for a Family in Katmandu.
So the father would be working the other side of the city, the
bridges over the river, would have been collapsed so he would
take him two days to get home in Wild.
What do people do? They're going to camp on the
football field. They have 23 Days In and Out of
Water and so on and so on time. And this was a story to get
people to concentrate their minds and what would actually
happen. And then in 2015, the earthquake
did happen and you could read this story book and more.
Let's turn over the page and say this is what's gonna happen
tomorrow and it more or less. Did they had a lucky Escape?
Because you're okay. Wasn't quite as big as 1934.
So instead of getting 100,000 people about 10,000 people James
Jackson, thank you very much.