What caused the earthquake in Turkey?

Turkey and Syria were hit by a devastating earthquake measuring 7.8 on the Richter Scale. More than 11,000 people have been killed, and many more are still unaccounted for. With us to explain what caused this to happen and what else might be in store is geologist and earthquake specialist James Jackson, from the University of Cambridge.

James - This has happened in Southeast Turkey along near the border with Syria. And it's a part of a very well known fault system, which we know a lot about. And it's there because Arabia is pushing North into Asia, crumpling the place up moving at about two centimetres a year, and Turkey is sliding out of the way sideways on a fault - think like a knife cut where rocks slide past each other sideways and Turkey is moving to the west out of the way of Arabia, which is moving North.

Chris - And how often do these sorts of events occur there?

James - There, I think the last one was around 200 years ago. But we know a lot about the history of that part of the world. People have lived there a long time. And if you go back over the last thousand years there have been quite a number of this sort of size. So it's not in that sense of surprise.

Chris - Is that because people have documented this or are there other records of how this happened?

James - It turns out that the various empires that ran that area, like the Byzantine Empire, the Ottoman Empire, were totally bureaucratic. And when these things happened, the emperor would send out parties to go and describe what had happened and it would all be recorded in the records and people have been through all that sort of thing.

Chris - So in essence then, if it's 200 years since it last slipped, that's 200 years worth of two centimeters a year movement and slippage which has been stored there and has gone all at once.

James - Yes, indeed. That's why it's moved. It'll have moved between five and 10 metres sideways.

Chris - So it's sort of horizontal. It's not up and down?

James - It's not up and down, it's sideways. If you are standing on one side, the other side moves to the left. That's how it works. We know a lot about this particular fault. It's been studied quite well.

Chris - How far out from the area where the slippage happens will the repercussions be felt? How far does that energy propagate dangerously?

James - You don't want to be really within about 20, 30 kilometres, there's quite a difference in terms of which direction you're in. So these things rip like a piece of paper and they rip from one end to the other and this one started in the South West and ripped up towards the North East. And in the direction in which it's moving like that, you get about twice the ground shaking. And that's why most of the damage is to the North East towards Kharamanaras and other places up there.

Chris - And once it goes, does it tend to release all the energy all at once or could there be more in store?

James - No, it ruptures about two kilometres per seconds. So this would've taken about a hundred seconds to do its stuff. So if you've been anywhere near it, you wouldn't have been able to stand up for a hundred seconds.

Chris - But if you've got 200 years worth of energy stored there, does it release 200 years of energy in one event? Or does it go and then wait a bit, couple of days go by and then...

James - You get after shocks. If you have a crack in the windscreen of your car, you know where it's going to go next. And all that's happening is a crack is releasing the stress by the crack and it all concentrates at the end of a crack. And that's what happens while you get aftershocks around these faults.

Chris - So is it done now or are Turkey bracing themselves? There may be more in store?

James - There'll be aftershocks from this earthquake for a year or so. They're not necessarily destructive and they should be smaller than the two we've just had. But on the other hand, they're going to hit buildings which are already damaged and vulnerable.

Chris - Right. And how will geologists like you now be studying this because every event like this, awful as it is, is a learning opportunity. How are people beginning to piece together what's going on?

James - Within a day or two we will know precisely what happened, where this fault moved within a meter, how much it moved within about a metre along its entire length. We can get that information from satellites. So satellites come over and they take a before and after picture, essentially, of the land, either with radar or optically, and you just compare the two and you can see how it moved.

Chris - And does that inform what might be going on next?

James - We do it because we want to know how these things work. You learn from it as you say, by doing this. Someone has to actually decide what you can learn. And the result of all that is that we can't say when the next earthquake's going to happen, but we are quite good at saying what will happen when it happens - in terms of the shaking, the distribution of the shaking, whether it moves up and down or sideways, all this kind of stuff, which is what the engineers and architects want to know. So if you then give that information to the engineers and architects and say, can you build something which will stay up? The answer is yes.

Chris - The classic line is it's not earthquakes that kill people, it's buildings. The number of lives lost here though seems dramatic. Is that just a reflection on how many people live there or is that just a reflection on how serious the event was?

James - It's not large compared to some of the past ones in Turkey. I mean, it is about right for this kind of earthquake in Turkey. And it's a tragedy. I mean, the same size earthquakes in places like Chile and New Zealand are not about killing people in these numbers at all because their buildings are better.

Chris - Is that because they haven't had one every 200 years, so they pay more attention?

James - So you'll feel one which scares you every year, and every 10 years we'll get one which really scares you. And then every lifetime you'll get one this kind of size.

Chris - And that focuses political minds. So buildings are built better, people are better adapted and prepared?

James - If you talk to people in that part of Turkey, and you say the last one was 200 years ago, they'll say every day it takes me two hours to get to work, to collect my children from school. I have problems with traffic, congestion, pollution, water supply. There's a war going on. And 200 years ago, it's a problem for my grandchildren's grandchildren. It just has very low priority. And that's the real difficulty. And that's because of the geology. It's because there are lots and lots of faults in Asia and each one doesn't have to move as often as around the Pacific.