"Just after lunchtime on March 11th, the most powerful earthquake ever measured in Japan shook the country." "It was big enough to shift the Earth on its axis." "It sent a tsunami ten metres high racing towards the mainland." "The Tohoku earthquake had unleashed on to Japan one of the great forces on the planet." "People had just minutes to save their lives." "The tsunami then triggered a near-meltdown in one of the country's nuclear power stations." "The disaster has claimed over 10,000 lives." "Almost twice as many are still missing." "When something as shocking as this happens, it's hard to see past the terrible loss of life and devastation." "Certainly, it makes you appreciate the power that our planet holds over our lives, our cities, over our civilisation." "And in that sense, it raises fundamental questions about my science - the science of earthquakes." "In this film, I'll be looking at the causes of this earthquake deep within the planet." "I'll be examining its consequences and finding out whether this earthquake could trigger another big one." "Two weeks after the earthquake, people are still struggling to come to terms with the scale of this disaster." "Aftershocks are a daily occurrence." "So far, there have been over 700." "Normally in Japan, earthquakes don't cause this kind of destruction." "But the events of the last fortnight have been far from normal." "As emergency crews help those left among the ruins, scientists worldwide are now starting to work out what made this earthquake so powerful and so deadly." "I've come to the Royal Society in London to piece together the anatomy of this disaster." "When I heard the news and watched those first images, it was clear that this was something different." "Something really unusual." "Big earthquakes like this are few and far between, and as an earthquake geologist, you're immediately intrigued as to just what happened." "Crucial evidence is already starting to emerge in the seismic record." "These are seismic traces, blow-by-blow accounts of earthquake jolts deep underground." "This happens to be a quiet morning in Japan." "3:00am, hardly anything happening." "There's a little rattle towards the end." "3.10, 3.20, nothing. 3:50." "4:00am - another little rattle." "But if this is a quiet day, then look at it when the big shock comes." "Here it is." "It's been quiet before 12:00pm, and then through the afternoon, and then here, 14.46, the big one strikes." "The needle just goes off the scale and then what happens is..." "Well, all hell breaks loose - just a storm of aftershocks that sweeps its way through juddering and jolting Japan." "But the thing is that it's wrong to think of this event just somehow in isolation." "What we can see if we take a longer view of this is that earthquakes are happening all the time in Japan." "Here is the big one, the 11th of March, big quake, and here are all the aftershocks, but two days before, another pretty big earthquake." "And that's the point" " Japan is just incredibly seismically active." "This seismic activity is all down to a fragile jigsaw of tectonic plates - giant slabs of rock which move across the planet's surface." "Heat generated by Earth's core keeps these plates constantly in motion." "Where they grind together, huge forces build up." "When the pressure gets too much, the edges of the plates suddenly slip... causing an earthquake." "This map shows where earthquakes happen in the world, something like 100,000 every year." "But 30% of those are up here in Japan." "You can see them, black dots all the way around here, past Alaska here, and down to California where the famous San Andreas fault line rips through." "Then over here, here's New Zealand." "The line of earthquakes goes right through it." "Christchurch had an earthquake last month." "That was small compared to Japan, and the reason for that you can see on this close-up." "Japan sits at the meeting place of at least four plates." "There's one here, one here, one here and one right underneath." "And these numbers here, 90 under northern Japan, is 90mm per year that the Pacific is moving towards Japan." "That's that much in a year." "So the reason why Japan is kind of earthquake country is because you've got all these plates meeting and all the stress gets concentrated under there." "To really understand how events unfold, you have to understand the time line of an earthquake." "This is the live TV feed from the Japanese parliament." "At 2:47pm, this appears." "This is an automatic alert." "It warns TV viewers that an earthquake has occurred." "Unaware of this warning, the delegates continue the debate as the announcer reels off a list of areas expected to be hardest hit." "ANNOUNCER READS LIST OF AREAS" "What you're seeing is the gap between the earthquake happening, and its shockwaves arriving in Tokyo." "But it's only a matter of seconds before those shockwaves strike." "Despite the obvious confusion above ground, below, a very particular sequence of events is beginning to unfold." "The earthquake starts with the sudden release of this immense pent-up energy in these massive tectonic plates." "And within a few seconds, huge seismic shockwaves race outward from the epicentre." "And the thing about shockwaves generated by earthquakes is that there are different kinds, but for the people of Japan on 11th March, there were two types that were important." "One is P waves - primary waves - which kind of push and pull the rocks." "And the other is S waves - secondary waves - which shear it from side to side." "P waves travel much faster than S waves, something like 10 times the speed of sound, but S waves, although they are 60% slower, are the ones that do all the damage." "The difference in the arrival times turns out to be absolutely crucial because sensors can detect P waves and can send out warnings to mobile phones and TV stations." "Although the gap between the arrival of the two types of waves is just a few seconds, that's precious enough time to get clear of buildings and to take cover before the dangerous S waves strike." "Of course, when the first tremor of an earthquake hits, nobody knows what's coming next." "And at first, it seems like many of the other ground tremors so common in Japan." "But soon, the severity of this quake becomes clear." "PEOPLE START SHOUTING" "Let me set the scene." "This is Tokyo, Friday afternoon on 11th March." "The P waves have just come through and the deadly S waves are starting to arrive." "And you can tell they're arriving because as we start to watch, these sky scrapers are starting to sway." "It's hard to see it on this view, but if you zoom in, you can really see it." "That sky scraper is just rocking back and forth." "And what must it have been like to be 20, 30 storeys up there as that sways back and forth?" "Absolutely terrifying." "LOUD CREAKING" "People immediately turn to the earthquake drills which have been rehearsed so often in Japan." "But as the intensity of this earthquake increases, it's clear that this is on a scale that nobody has anticipated or rehearsed for." "The shockwaves are starting to tear at the fabric of the city." "Earthquake right now." "This is actually moving." "See the cracks moving?" "That crack was not there." "DOG BARKS WILDLY" "This footage just absolutely takes your breath away." "What we're seeing is a path of concrete or asphalt just being ripped apart by the shaking." "See how it's moving up and down." "The reason for that is because although the shockwaves come from tens of kilometres down and travel upwards, it's in the uppermost few metres that they're at their most destructive, because as the vibrations move from the solid rock into the looser sand and muds of the soil," "the vibrations amplify so they get more destructive." "Look at that." "You can see the whole thing moving back and forth." "The whole ground is behaving like jelly." "It's shaking for a long time." "From start to finish, the earthquake rupture is five minutes." "Imagine standing for five minutes in the park and it's like the open sea - you're getting tossed around." "The reason for the land moving back and forth is because under there, there's water trying to get out." "It's been trapped in the soil and there earthquake has released it." "It's bursting open." "There it goes." "This is called liquefaction - the ground is literally turning into a liquid." "After a few minutes, the shaking reaches its peak." "So great are these forces that they are felt in towns and cities across much of Japan." "The spread and extent of this shaking has already been mapped by seismologists." "The red parts show the areas which shook hardest." "Great swathes of the Japanese mainland are severely affected." "You probably heard on the news that this event of March 11th measured nine on the magnitude scale and that scientists have labelled this a mega-thrust earthquake." "But what does all that mean?" "It's been calculated that the energy released in this event was 600 million times greater than that released in the nuclear bomb that destroyed Hiroshima." "But it's just so hard to get your head around." "The thing is as a geologist, you're always looking at the big picture." "And for an earthquake like this, a giant quake." "it doesn't get much bigger." "Which is why the global effects of this are truly staggering." "Huge forces were released by this earthquake." "They shifted the Earth's axis by up to 25cm." "They changed the shape of a planet, which affects the speed at which it rotates in space." "The result?" "The length of each day is now a tiny bit shorter for all of us." "It's hard to imagine how an earthquake can reshape a planet, but consider this " "Japan's East coast has lurched four metres out towards the Pacific, and sunk by over a metre." "But what made this earthquake so big?" "And what triggered it?" "To find out, I visited the University of Ulster, in Belfast." "I've come here to meet one of the top earthquake scientists in the world and someone that I think has got a real handle on what's happened with the Japanese quake." "Much of the data's still coming in, but already the picture is becoming clearer." "Professor John McCloskey is a pioneer of earthquake research." "He's spent years studying seismic activity across the Pacific region where the earthquake occurred, and, crucially, he's studying how stress builds up in the Earth's plates and how that can set off earthquakes." "Well, to understand why an earthquake ends up being a big earthquake, we have to think really about hundreds of years of very slow, steady accumulation of stress." "The very interesting thing is that this now is a process where we have a very highly stressed fault, with patches of very high stress, and on to that we just put the smallest amount of stress loading," "and sometimes that can have an amazingly large effect." "Just two days before the earthquake struck, another quake, measuring 7.2, occurred nearby." "Professor McCloskey believes that the stress transferred by this smaller, earlier earthquake was enough to trigger the big one." "So this is the situation, the 7.2 earthquake started here and it shed stress in the surrounding region." "And the outside of the bull's-eye is an area of increased stress." "This area of additional stress covers the location of the big earthquake on March 11th." "And what's remarkable is how minimal the force of this additional stress actually was." "The amazing thing is that amount of stress that's represented by these red colours, is actually the amount of stress in a gentle handshake." "The force of an actual handshake was all it took to trigger the earthquake which made headlines around the world." "So a big earthquake, a magnitude nine, needs a handshake of stress to start it off." "That's phenomenal." "A handshake is all that it takes." "It's an extreme." "It is the straw that breaks the camel's back." "Notice the straw, it doesn't supply the force, it just supplies that extra small load which is all it takes to trigger, in this case, the release of such enormous amounts of energy." "And that energy had to go somewhere." "The violent earthquake now shaking Japan had already unleashed another force, one far more deadly." "About three minutes after the earthquake," "Japan's Meteorological Agency broke into TV broadcasts with another warning." "Analysis of the earthquake data had predicted it would cause a tsunami." "They were right." "A giant wave was racing across the ocean towards Japan." "But people seemed to have little sense of what was in store." "After all, many buildings appeared to have survived the earthquake." "And tsunami warnings are common here." "But in reality, people in some parts of the coast, now had just 20 minutes to escape before the wave struck land." "Tsunamis are fairly rare events that are not entirely understood." "But that may change because there's more footage of this tsunami than any other in history." "For scientists, that footage from news helicopters and mobile phones forms an extraordinary body of information." "And the hope is that by studying these incredible images in detail, we'll understand where the tsunami's great destructive power comes from and also how to survive them." "The ferocious power of the tsunami began deep under the sea inside the planet." "The huge energy released by the earthquake ruptured a 300 kilometre stretch of the Earth's crust." "It forced the seabed up perhaps ten metres, driving a giant column of water up above the surface of the ocean." "The tower of water collapsed, sending a tsunami racing at 200 kilometres a hour east across the Pacific ocean, and west towards Japan." "The tsunami consisted of up to ten individual waves, each about a kilometre apart." "This remarkable footage was filmed on the Matsushima, a coastguard vessel 5 kilometres out to sea off Japan's north-eastern coast." "It records the progress of the tsunami through the ocean." "On the bridge, the crew capture the moment they crest the wave." "CREW GASP" "As it neared the coast, the tsunami became much more dangerous." "In the shallow water, the individual waves began to catch up with each other, becoming higher." "The tsunami had become a giant wall of water." "24 minutes after the earthquake, the tsunami hit Japan's northeast coast." "In places, it was 15 metres high." "That's as tall as a three-storey building." "PANICKED VOICES" "GASPING" "Our vulnerability in the face of the Earth's natural forces, was captured as never before." "These satellite images show how the landscape was utterly transformed." "In Japan, many of the communities are forced to live on the coastal plain just because the interior is so mountainous and they know the coastline is prone to tsunamis, but what this terrifying footage shows is just how utterly uneven" "the balance is between people and nature in this coastal zone." "This is the fishing port of Miyako, home to 60,000 people." "Although I've seen this footage loads of times on the news, what I hadn't realised is this here is a ten-metre coastal wall, a sea wall designed to protect against tsunamis." "And you can see what's happened." "The water's got so high it's completely swamped it." "Overwhelmed it." "Look at that." "40 per cent of the Japanese coastline has a sea wall like this." "And the point is that in times like this, when it's huge waves, rather than be a barrier, rather than protect, they are actually giving a false sense of security because once the water's over here, it just keeps going." "The wave here was ten metres high." "The same as the sea wall." "But during the earthquake, the whole coast had dropped by about a metre." "so the wall offered little defence." "It looks like the tsunami has engulfed several cities in Miyagi Prefecture." "Live footage of Miyagi as the tsunami has struck the area obviously engulfing farms, homes, alongside the river." "In Sendai City, this is, in Miyagi Prefecture." "SCREAMING" "What we are seeing here is the tsunami front coming in this bay near Sendai." "You can see this wall of water, it's not a wave, but a wall of water just ploughing through." "You can see minibuses, cars coming through - it's a wall of metal and concrete and timber ploughing forward." "Look at this - there's cars desperately trying to get out of the way." "It just keeps coming." "The sheer relentless onslaught of it all is just what's really striking." "You can see fire, some building has been set on fire." "The tsunami goes into these drainage ditches and look, there's one wave coming up and look there's another one coming down." "It's like a pincer movement." "How you could survive that?" "And the point is that this land is so flat, that this wall of water just travels inland for ten kilometres." "So those people escaping have ten kilometres to try to escape." "PANICKED VOICES" "These disturbing scenes show the tsunami striking the fishing port of Minamisanriku." "They just demonstrate how people react in the face of disaster." "This is a town of 17,000 people and you can just see their wooden houses being swept away." "This community received a warning, enough warning for people to get up on to high ground and, in this case, film the wave as it comes on." "But many people delayed - perhaps going back to their houses to collect possessions or there little group here that look as if they are carrying an elderly relative." "And down in this corner, a real human drama unfolds." "At first, they don't seem too concerned, the water's moving slowly, and they're moving up the slope, but very quickly the wave accelerates and the pace gets picked up and suddenly they're right on the frontline" "and the water's just coming across and speeding up." "And suddenly that's it, they're trying to escape." "It doesn't matter how many times you do tsunami drills, when the terror strikes, those split second decisions made in the heat of the moment, ultimately decide if you live or die." "Japan was hit by two very different forces on March 11." "The earthquake they coped with pretty well." "The tsunami completely overwhelmed them." "The final major wave hit Japan about three and half hours after the earthquake." "The same pattern of destruction was repeated in countless towns and villages along hundreds of miles of coastline." "Some of the towns along these shores which can trace their history back over a millennium had virtually ceased to exist." "The people in Japan get less than a minute's warning of the earthquake and maybe 10 to 20 minutes' warning of the tsunami." "And in both cases, it just wasn't long enough." "And one question that generation after generation of geologists have been wrestling with and one that absolutely intrigues me is - why can't we predict earthquakes?" "This earthquake happened in a country whose huge seismic activity is the most studied in the world." "Across Japan, more than 1,000 seismic instruments record each twitch of the ground, and GPS devices every 20km track the movement of the underlying plates." "But even so, nobody was able to predict when this earthquake would happen." "But there's one place in the world where scientists really thought they were getting close to the holy grail of earthquake prediction." "This line of hills with the trench cut through the middle is the San Andreas Fault in California." "The world's biggest attempt to try to predict earthquakes took place here." "In a small town on the fault, there seemed to be a pattern of earthquakes occurring at regular intervals." "Scientists hoped they could predict the next one by spotting telltale clues in the movement of the ground." "This is Parkfield." "26 years ago, it seemed this insignificant dot on the map held the key to predicting earthquakes." "It began when a team of geologists noticed something unusual here." "Parkfield had been repeatedly struck by earthquakes." "It was in the '70s and early '80s, it was recognised that there was a sequence of magnitude-six earthquakes that repeated the same stretch of the San Andreas Fault every 20-odd years." "It didn't take too much imagination to extrapolate and say, "OK, the next one ought to be in the late '80s."" "In 1985, geologists began setting up hundreds of instruments here to track the build-up to the next quake." "They believed it would occur some time between 1987 and 1993." "Well, what you're hoping to see - the analogy is a stick breaking." "So, in the long term, you're bending the stick, you see it deform, and then maybe just before the stick goes "snap", you'll hear "crack, crack, crack" or something like that." "Now they had narrowed down the time window and knew where it was going to strike, this was science's best chance to see the build-up to an earthquake." "Millions of dollars flooded in to fund the research." "All they had to do now was just sit and wait." "We had some creepmeters that measure fault slip, some geochemical experiments, strain meters, global positioning system." "1993 came and went with no earthquake." "So did 1994, '95 and '96." "Our guess was basically - what'll we call it?" "Ambitious or optimistic." "In fact, the earthquake didn't happen until 2004." "And then it struck without warning." "Whatever the trigger, it had eluded the instruments." "Despite all their efforts, the geologists had failed to spot any telltale clues." "It was like the fault was quiet, quiet, quiet." "And then it broke." "And it was a fairly negative result." "We were waiting to catch that precursor with all these instruments, and nothing happened." "The failure of the Parkfield experiment was a significant moment in earthquake science." "Earthquakes are sensitive to small triggers far below the surface of the planet, too far down to be measured." "After Parkfield, trying to spot clues to when an earthquake would happen seemed too simplistic." "In Japan, events were to push earthquake science in a very different direction." "The catalyst was another failure of prediction." "In 1995, the city of Kobe was devastated by an earthquake." "6,000 people were killed." "The disaster was so significant for science because no-one had thought the city was at risk." "Now the most urgent task was to identify which other areas of the country were most threatened by earthquakes." "To try to find out where," "Japanese scientists began to place hi-tech seismometers all over Japan to try and detect the slightest little movements of the ground." "Alongside, they placed GPS devices to track the build-up of strain in the rocks below, and after all this work, this is what they came up with - the earthquake hazard map of Japan." "The thing about what this map represents is really where earthquake science is in Japan today, because what it shows is the areas that are most at risk of being affected by an earthquake, with those that are most vulnerable coded red." "Now, this map was made in 2010, just last year, but you can see one of those red danger zones is right here" " Sendai, which is the city that was closest to the earthquake on March 11." "So, can we predict when the next big earthquake will strike?" "No." "But can we forecast the areas that will need to prepare for one?" "Yeah, I think we can." "And that is a big advance." "'Professor John McCloskey is pushing the boundaries 'of this kind of forecasting in another of the world's seismic danger zones.'" "In Sumatra, we have the pieces of the jigsaw puzzle which will allow us ultimately not to predict earthquakes, but to be able to say that there are certain sections of these fault systems which are more likely to fail" "in the next ten years than any other sections." "But I think we will globally be able to identify a series of earthquake hot spots." "We won't be able to say when the next earthquakes will happen there, but we will be able to identify earthquakes or places that will give us earthquakes of magnitude eight or bigger, that will produce really damaging shaking," "that will produce secondary hazards like tsunamis and landslides and that will be potentially absolutely lethal for populations." "So earthquake science is working today in the absence of prediction..." "Yeah. ..to help people prepare and to survive future big earthquakes." "'Of course, preparation for natural disaster 'is all about knowing what risks to expect.'" "But in Japan, what started as a natural disaster unexpectedly became a man-made one." "In one small part of the coast, the crisis was entering a new critical phase." "A battle was on to stop radiation escaping from this power station." "Immediately after the earthquake, seismic sensors had automatically triggered the shutdown of four nuclear power stations across Japan." "Among them was the Fukushima No.1 plant, 240km from Tokyo." "It's standard procedure after an earthquake to insert control rods into the core of a reactor to stop the nuclear chain reaction." "But elsewhere in the plant, there was a problem." "The earthquake had knocked out the power supply to the reactor's cooling system." "Looking at this map, you find yourself wondering why anyone would build a nuclear power plant in Japan, a country with nearly a third of the world's earthquakes." "You can see them all here in red dots scattered along." "There you can see the outline of Japan with the nuclear power plants." "It's a decision that's been forced on them by geology, because this is a nation with a real thirst for energy and yet no real oil or gas of its own." "It's got 17 nuclear power plants dotted around the coastline because they need massive amounts of water." "Of course, the coastline is where people live, so it's an example, really, of an uneasy bargain that's been struck between people and the planet." "But Japan's engineers prided themselves on having made their nuclear power stations quake-proof." "This reactor complex you can see them - one, two, three, four - was built with earthquakes in mind." "It was designed to withstand a magnitude 7.9 shake." "With the sea just here, they built a sea wall 6m high to protect against tsunamis." "But what they didn't plan for was an earthquake so big or a tsunami so high." "If that wall had just been 1.5m higher, it would have kept the wave out." "But as it was, it overtopped it and set off a terrifying chain of events." "What this represents is a catastrophic failure of imagination." "The earthquake had severed the power supply to the cooling system." "Then the tsunami swept over the sea wall and destroyed the backup generators." "Now the engineers were forced to rely on batteries to run the cooling system." "And these had just eight hours' life." "When THEY ran out, the cooling system died." "Although the main nuclear chain reaction had been stopped, when atoms of uranium are split, other radioactive elements, like iodine and caesium, are released." "As they decay, they create heat." "Without a cooling system, there's nothing to stop the reactor overheating." "A day later, an explosion blew away much of the roof and outer walls of reactor number one." "As the fuel rods heated up, the cladding around them reacted with steam and produced hydrogen gas." "The gas exploded, propelling radioactive elements into the atmosphere." "Then explosions hit two other reactors, and levels of radioactivity around the plant rose." "Now Japan and the world were haunted by uncertainty." "Just how dangerous was the radiation that been released?" "In this nation, radiation evokes a particular dread." "As fear spread, hundreds of thousands of people living near the plant were evacuated." "Some governments advised their nationals to leave the country." "But it was the workers who stayed behind at the plant that were most at risk." "Some have been exposed to very high levels of radiation." "Their ongoing struggle to keep the reactors cool is heroic." "But the continuing inability to bring the plant under control has only fuelled anxiety." "I wanted to ask Professor Jim Al-Khalili, a nuclear physicist, just how dangerous this release of radioactivity was." "The caesium and the iodine, I mean, what can they do to you?" "Both iodine 131 and caesium 137, if you breathe them in, or you ingest them through food or through water, and they collect inside the body, the particles they spit out, can damage cells, can even cause cancer." "I've been hearing about these plant workers getting doses of 400 millisieverts per hour and sometimes an instance of 10,000," "I mean what are these units?" "What do they mean?" "The sievert, or the millisievert in this case, is a unit of measurement." "It tells the level of exposure to the radiation that we have." "I think it's very useful to compare it with how much radiation we're exposed to otherwise normally." "So if you think the base level, no radiation is zero, all of us are exposed to natural background radiation of about two millisieverts, OK." "So that's what we get from the atmosphere, from the food we eat, coming up from the ground." "If you have a CT scan, then that will give you something like ten millisieverts." "So you don't want to have too many of those." "A typical nuclear worker would have a safety margin of about 20 millisieverts per year." "Per year?" "So 400 millisieverts an hour is somewhere away over there?" "Is way over there, absolutely." "Yes, that's where the concern is." "What about the wider community?" "I mean, how concerned should they be?" "Well, I think it's important to understand just how far this the radiation will extend." "So this is the Japanese government's imposed exclusion zones." "So the plant is here and you have a 20 kilometre radius exclusion zone and the 30 kilometres outside it." "Beyond the exclusion zone, the risk is very, very low, it's negligible." "It's no higher than natural and you can compare it with just natural radiation, depending on what part of the world you live in." "The worry is how far the air will carry this radioactive material, the plume, and as far as we know, it was travelling out east into the Pacific, not inland." "But some radioactive fallout has come on land, hasn't it?" "Because there's been talk of iodine in the water in Tokyo." "We have to remember this is the other way that this radioactivity can spread, other than just through the air." "If it gets into the water supply, it can get into the food chain, then that's the way that the Japanese population might ingest it and that is cause for some concern." "And how much concern then, iodine in the water?" "Well, I think, we've heard that what they measured was that the level was higher than what might be deemed safe for young children." "But iodine has a half-life of just eight days, and so eight days from now, the level drops to half of what it was before, so it very quickly drops down to manageable and safe levels." "But it's not sounding as if this is a kind of no-go Chernobyl-type disaster zone at all?" "No, I mean, we certainly know this isn't a Chernobyl." "So, basically, we've got to keep this into perspective?" "It's certainly a major public concern and we understand that people are afraid of radiation - it's invisible, it can cause cancer, of course there are worries." "But people need to understand the real risks and, yes, keep things in perspective." "What this disaster illustrates so starkly is a failure to plan for events that nobody wants to imagine." "But when it comes to nuclear power, the stakes could not be higher in that bargain we strike with the planet." "You know this isn't the first time that a Japanese nuclear power plant has been breached during an earthquake." "In 2007, a magnitude 6.6 seismic jolt struck the country's largest plant and caused a minor radioactive leak, and around the world the 440 odd nuclear power plants, something like a fifth lie in these seismically active areas." "So if we think that we can design for earthquakes, these are going to be the ultimate test." "The triple calamity of the past two weeks - earthquake, tsunami and threat of nuclear meltdown - have left this country in a state of shock." "The scale of the human tragedy is only just sinking in." "10,000 killed, over 17,000 missing, an estimated half a million displaced." "This has become the most recorded earthquake in history, and it's set to be the most studied." "Scientists of all disciplines are starting to analyse this disaster in incredible detail." "And the hope is that that work will ensure that next time what begins as a geological event somewhere in the world won't end up such a human tragedy." "One of the most pressing questions that researchers are already trying to answer is this - what is happening to the tectonic plates across the world in the aftermath of the earthquake?" "A lot of people have been asking me about whether the earthquake that happened in Japan has got anything to do with the quake that struck Christchurch last month." "Is it part of a seismic chain reaction?" "On a global scale, no, I don't think they're related, but on a local scale, we already know that one earthquake can affect another, and we know that the March 11th quake was triggered by stress" "that shifted from another smaller quake just a couple of days before." "The question that geologists are really trying to get to grips with is could the events of the last two weeks be the trigger for another earthquake, perhaps Japan's big one, one directly under Tokyo?" "Over 30 million people live in and around Tokyo, a quarter of the country's population." "An earthquake centred on this city is what the Japanese call the big one." "And it's such fear today because of what happened to this city in 1923." "On September 1st, shortly before midday," "Tokyo was struck by a large earthquake." "The ground shook for at least four minutes, bringing down swathes of the city." "It claimed over 100,000 lives and left almost 2 million without homes." "But here's the thing, this earthquake is estimated to have measured 7.9 on the magnitude scale, more than ten times smaller than the earthquake two weeks ago." "The question of how the recent earthquake might now affect Tokyo is one that John McCloskey is studying." "He's produced a very revealing map showing what's happened under Japan since the earthquake." "It displays changes in stress levels deep under ground." "So the blue area is where the stress has been released, stress has dropped down, and the red area is where the stress has gone up." "So what we left with is a picture of areas that are blue, in which the stress has dropped, and, therefore, the risk of other earthquakes has probably dropped." "And red areas, where the stress has increased and the risk of other earthquakes has increased accordingly." "It's looking as if a lot of the stress increase is around the area to the south, and that's the area of Tokyo then." "That's absolutely true because most of the slip happened up here, most of the interaction stress is forced towards the south." "That is evidenced by the hundreds of aftershocks that have happened in this area." "So is it fair to say that the big earthquake in the north has increased the risk of an earthquake in the south?" "The big earthquake in the north is already increasing the risk." "It is already generating earthquakes in the south." "Magnitude 7.9 earthquake is a direct result of the stress shed from this earthquake in this region." "This is already happening." "It's early days, the data are still coming in, but it does seem like the recent earthquake makes the possibility of a big quake in Tokyo more likely." "Facing up to the threat of earthquakes is vital." "And for me, it's not about predicting when they will happen." "It's about how you protect yourself for when they arrive." "When I was in Tokyo a few years ago," "I saw the latest innovations in earthquake-proofing the city's buildings." "Normally the rigid walls of tall buildings will shatter under the pressure of a big earthquake." "But in Japan, special features are added to absorb these forces and make the superstructure flexible." "Here at Tokyo's Nihon University, bendable braces have been designed for this laboratory building." "Professor Masao Saito is the earthquake engineer responsible." "Can you tell me about the system you have got here to reduce earthquake shaking?" "These bracing system are arranged along the whole wall." "So you have this bracing system all along the wall." "Hundreds of these braces ensure the laboratory is twice as flexible as a conventional building." "I'll show you through this model." "As Professor Saito's model shows, when an earthquake hits, each brace contains a piston, which acts like a shock absorber." "If the frames moves, the piston works in this direction." "So it's dampening down everything." "Dampening here." "Beautiful." "So amidst all the tragedy of the past few weeks, there's on image that I think holds hope." "This building swaying in the earthquake, but remaining standing." "Japan leads the world in designing buildings that can survive earthquakes." "Sure it's terrifying to be inside one when a quake strikes, but the simple fact is that in many parts of the world these sorts of shocks would reduce a building to rubble." "Things could have been very different in Japan if the earthquake had struck not offshore, but under a major city." "The thing is, this was a huge earthquake and, actually, comparatively few buildings fell down." "And that's the point, really." "It's possible to engineer structures not to fall down in earthquakes and that more than anything else is what we've got to take forward." "Ten of the 20 largest cities in the world are located in seismic danger zones." "For the millions of people living on tectonic boundaries, the risk of earthquakes is inescapable." "The hope has to be that we'll build our cities better to help people survive them." "We know where the world's most lethal earthquake zones are." "And in the major cities that lie along them, we know where the big danger areas are." "It's true that we can't predict earthquakes but we can anticipate them and we can build for them." "For me, what the events of the last two weeks have really brought home is that we need to continue to spend time, money and effort preparing for the looming seismic threats ahead." "It really is the only way forward." "Subtitles by Red Bee Media Ltd" "E-mail subtitling@bbc.co.uk"