An earthquake off the north-east coast of Japan puts the region on high alert, but a tsunami warning is lifted after 90 minutes.
Japan: Earthquake prompts Fukushima evacuation
Authorities in north-east Japan ordered a general evacuation and workers at the damaged Fukushima Daiichi nuclear plant took shelter after an earthquake triggered a new tsunami warning.
However, the tsunami warning was lifted after 90 minutes and the earthquake - with a magnitude of 7.1 - did little obvious damage.
Fukushima officials said the quake had no detectable effect at the plant.
Last month's 9.0 earthquake set off a tsunami which devastated the region.
Shelter
The earthquake - at a depth of 49km (32 miles) - struck off Japan's north-east coast, close to the epicentre of the 11 March quake.
All seven of the workers at Fukushima Daiichi were safe, a spokesman for plant operator Tepco told a news conference in Tokyo.
"They have not been injured and they have all taken shelter in our seismic-resistant building. We are continuing to inject water, or we are continuing the injection operation at reactors 1, 2 and 3," said the spokesman, whose name was not given.
The workers are trying to keep the damaged reactors cool to stop further releases of radioactive material.
Thursday's quake struck at 2332 local time (1432 GMT) on Thursday, 118km (78 miles) north of Fukushima, 40km offshore.
First reports said it had a magnitude of 7.4 but that was later revised downwards to 7.1, according to the US Geological Survey (USGS).
Last month's earthquake had a magnitude of 9.0 and struck at 32km deep.
USGS geophysicist Paul Caruso said Thursday's quake struck at about the same location as the 11 March quake, the AP news agency reported.
The quake was strong enough to shake buildings in Tokyo, 265km to the south.
"The earthquake was moving in an up-and-down motion," Miri Gono in Tokyo told the BBC by e-mail. It started off with small shakes, then shook bigger. I was alone in my house with my brother and we were so scared... We took our bottles of water and hid under the table."
Japan's meteorological agency issued tsunami warnings and advisories for a stretch of coast 420km long, from Aomori prefecture in the north to Ibaraki prefecture in central Japan, just north of Tokyo.
Hundreds of aftershocks have shaken north-eastern Japan in the wake of the earlier earthquake, but few have measured higher than 7.0.
About 28,000 people are dead or missing, and hundreds of thousands were left homeless after the tsunami which ripped through north-eastern Japan.
Radiation levels in towns north of the stricken reactor are
particularly high (Image: Christian Alund/Greenpeace)
The readings were taken by the Japanese science ministry, MEXT, and reveal high levels of caesium-137 and iodine-131 outside the 30-kilometre evacuation zone, mostly to the north-north-west.
Iodine-131, with a half-life of eight days, should disappear in a matter of weeks. The bigger worry concerns caesium-137, which has a half-life of 30 years and could pose a health threat for far longer. Just how serious that will be depends on where it lands, and whether remediation measures are possible.
The US Department of Energy has been surveying the area with an airborne gamma radiation detector. It reports that most of the "elevated readings" are within 40 kilometres of the plant, but that "an area of greater radiation extending north-
west… may be of interest to public safety officials".
$6.8 billion needed to ready US for the next big quake
How a 7.8-magnitude earthquake might spread
along the San Andreas fault (Image: David McNew/Getty)
The recent magnitude-9.1 megaquake and the tsunami that followed it showed that Japan was not fully prepared for so violent a tremor. If even a country that suffers frequent earthquakes wasn't ready, what of the US, which itself contains several seismic hotspots?
Over the past two decades, the US has made considerable advances in fortifying its cities against quakes, but geologists and engineers agree that there is still much to be done. In a National Research Council (NRC) report published today, they have outlined just what that means.
The National Earthquake Resilience report is particularly concerned with the possibility of a "Katrina-like earthquake": not just a moderately damaging tremor, but a cataclysm rivalling the 1906 San Francisco quake, estimated at magnitude 7.9, which probably led to thousands of deaths.
Geologists fear that because of the US's relatively unshaken recent history, its citizens have been lulled into a false sense of security, believing that a devastating earthquake is unlikely to strike the country – although it's not even 50 years since Alaska felt the force of the second largest quake in recorded history. The magnitude-9.2 Prince William sound event led to 115 deaths in Alaska alone.
The NRC report recommends three major goals: raising understanding of earthquakes; developing cost-effective measures to reduce the effects of earthquakes on individuals, the built environment and society at large; and improving the earthquake resilience of communities nationwide. Over 20 years, reaching those goals is likely to cost $6.8 billion.
Science Daily (Mar. 14, 2011) — While Japan's 8.9-magnitude earthquake and accompanying tsunami represent a devastating natural disaster for the country's residents, scientists should also seize upon the massive temblor as an important learning tool for future quakes around the world, including the Pacific Northwest coast of the United States, according to experts from the Woods Hole Oceanographic Institution (WHOI).
WHOI geophysicist Jeff McGuire said such lessons may be particularly germane to residents of Northern California, Oregon, Washington and Vancouver--a region he said, could be subject to a similar quake/tsunami scenario. "Today's earthquake happened on a subduction zone thrust fault where the Pacific plate subducts, or dives, under the Japanese islands," he said. "Japan regularly has large earthquakes and tsunamis all along its east coast due to subduction.
"The west coast of the U.S., offshore of Oregon, Washington, Northern California, and Vancouver Island Canada, has a similar subduction zone that we think had similar size earthquakes regularly in the past, based on geologic evidence. The last one was in AD 1700, and they have a 250- to 500-year repeat time. There are no historical records from Oregon/Washington at that time, but the tsunami it generated was so large that it killed people in Japan."
McGuire has also studied foreshocks extensively, a phenomenon in which a smaller quake seems to foreshadow a larger one. "A few percent of earthquakes will trigger an event that is larger than the first event," he said.
That scenario may have been at work in the Japan quake -- formally identified as the N Honshu earthquake, according to WHOI Senior Scientist Jian Lin, currently on a research cruise in the Southern Ocean aboard the Korean icebreaker R/V Araon. Lin noted that a sizeable foreshock preceded the Japan quake.
"What is noticeable about the March 11, 2011 quake is that there was a magnitude 7.2 foreshock [on March 9], which is only 40 kilometers (km) away from the epicenter of the mainshock," said Lin, who has studied large quakes extensively, including last year's major quakes in Haiti and Chile.
"Foreshocks have been used previously as a tool for forecasting larger earthquakes," he said. "I am sure that we will be looking closely at this and other foreshocks."
The Araon started its mission in Christchurch, New Zealand, which experienced its own damaging earthquake this February. Now, heading back to Christchurch, it may encounter the remnants of the Japan tsunami -- albeit perhaps barely noticeable at the ship's current location. "Our cruise started with the Christchurch earthquake in New Zealand, and ends in sailing through a tsunami caused by the great Japan earthquake," Lin said.
The magnitude 8.9 quake struck 125 km off shore and about 370 km northeast of Tokyo, Lin said. It is likely to be the fifth largest earthquake ever recorded by instruments, he added.
Working on shipboard computers, Lin said that as of Friday afternoon, March 11, "I have already received notes of more than 40 aftershocks with magnitude greater than 5.8.
WHOI earthquake seismologist Jeff McGuire has studied foreshocks extensively, a phenomenon in which a smaller quake seems to foreshadow a larger one. He and his colleagues have developed a new suite of ocean bottom seismometers (OBSs) capable of accurately recording both foreshocks and mainshocks "A few percent of earthquakes will trigger an event that is larger than the first event," he said. (Credit: Photo by Tom Kleindinst, Woods Hole Oceanographic Institution)
"One of the areas hit by the tsunami, Sanriku, was hit by previous tsunamis, including a tsunami caused by a 1933 magnitude 8.1 quake that killed 3,000 people, as well as the tsunami from the 2010 magnitude 8.8 quake in Chile," he said.
He compared the current quake to the 1923 great Kanto earthquake of magnitude 7.9, which he said marked the beginning of modern seismology in Japan. "Although that was smaller than the current quake, it struck very close to Tokyo and Yokohama," Lin said. It caused more than 142,000 deaths and also caused a tsunami in the Sagami Bay with wave heights as high 20 to 39 feet in some areas.
McGuire and others have long been aware that a similar scenario could occur off the Pacific Northwest coast.
Led by McGuire, John Collins and Ken Peal, WHOI currently has ocean bottom seismometers deployed offshore of Vancouver Island to study the properties of the fault system there.
"Over the next five years, WHOI will be involved in the National Science Foundation's Cascadia Initiative," McGuire said. "This will be the first large-scale instrumentation of the fault offshore of Oregon and Washington that is capable of generating a magnitude 9 earthquake and tsunami."
In the meantime, Lin and his colleagues are heading to Christchurch, having just finished a very successful cruise of hydrothermal, geophysical, and geochemical sampling cruise of mid-ocean ridge segments "that nobody has studied before," he said.
Lin plans to survey the Christchurch earthquake zone and the widespread liquefaction before returning to WHOI on March 15.
After that, he will work with colleagues at the USGS National Earthquake Center in Menlo Park, Ca., to investigate both the Christchurch and Japan quakes
CHIANG RAI, Thailand — A severe magnitude 6.8 earthquake struck a sparsely populated mountain area in the Golden Triangle region of northeastern Myanmar on Thursday, with tremors being felt over a wide radius.
News agencies reported Friday that as many as 50 people had been killed, a bridge was destroyed near the epicenter, homes were damaged in southern China and buildings shook as far away as Bangkok; Hanoi, Vietnam; and Yangon, Myanmar’s largest city.
Buildings were damaged near the epicenter in Myanmar’s Shan State and villagers felt aftershocks for several hours, said an official with World Vision, a children’s aid agency, in Myanmar. Reports of any damage and injuries, though, were slow to emerge overnight from the remote mountains and valleys.
The area affected is landlocked, and no tsunami warning was issued.
One woman was killed in this Thai border city, about 70 miles south of the epicenter, when a wall fell on her as she was sleeping, Thai television reported. Some people here said they were shaken from their beds or ran into the streets. One woman attending a funeral said she clung to a pole to stay upright.
“I felt I was swaying like a child in a cradle,” the woman, Nutpisut Thongkika, a 50-year-old teacher, said in a telephone interview from Chiang Rai. “The situation here was very chaotic when the earthquake hit.”
Thai television said no serious damage was reported in Chiang Rai.
Many tourists in nearby Chiangmai fled their hotels and remained for hours in the streets.
The United States Geological Survey said the earthquake was just six miles deep, meaning that severe shaking could have caused major damage to buildings in a wide area. It also reported a smaller quake, of 4.8 magnitude, about a half-hour later.
Buildings shook for more than a minute in China’s nearby Yunnan Province and many residents fled their homes in Nanning City, the capital of Guangzi Autonomous Region, the Xinhua news agency reported. It said officials were investigating the extent of the damage.
Another earthquake on March 10 in Yunnan Province in southwest China took 26 lives and destroyed a number of schools, Xinhua reported. The tremors Thursday caused panic in Hanoi, 380 miles to the east of the epicenter, where residents said they heard the shattering of windows, the Vietnam News Agency reported. Tall buildings shook and chandeliers swayed in Bangkok, 480 miles to the south.
Hours after the quake, people in villages near the epicenter remained in the streets afraid to return indoors, said Jenny McIntyre, communications manager in Yangon for World Vision, a children’s aid agency.
“These are subsistence farmers, simple people who have got simple water systems which will potentially be threatened,” she said, adding that the damaged bridge had cut off an area near the epicenter.
She said she also felt the tremors in Yangon, 350 miles to the southwest. “I suddenly felt really sick and strange and I realized that everything was rocking and the lightshades were all rocking,” she said.
Wongdeun Kongcharoen, 34, a hotel manager in Chiang Rai, said the earthquake cracked the walls of houses and scattered glassware and other belongings in all directions.
“People here are still nervous and staying outside,” she said about two hours after the tremors. “We feel like the situation that happened in Japan. It was so scary.”
She said a Japanese friend told her the shaking was light compared to earthquakes in that country. “But this was the first time for us to experience a situation like this,” Ms. Wongdeun said. “So that’s why we were still outside and still scared.”
Poypiti Amatatham contributed reporting from Bangkok.
Tokyo water 'unfit for babies' due to high radiation
Tokyo's tap water is unfit for babies to drink after radiation from Japan's quake-hit nuclear plant affected the capital's water supply, officials said.
Radioactive iodine levels in some areas were twice the recommended safe level.
People in Fukushima prefecture, where the nuclear plant is located, have been told not to eat certain vegetables because of contamination worries.
Workers have been temporarily evacuated from the plant after black smoke was seen rising from reactor No 3.
Engineers have been trying to cool the reactors and spent fuel rods to avoid a major release of radiation, after power to the cooling systems was knocked out by the earthquake and tsunami.
The authorities are warning people living in Tokyo not to allow babies less than a year old to drink water from the tap.
The level of radiation picked up in tests carried out on Tuesday was more than twice the level that is safe for infants to drink.
But officials have stressed that children would have to drink a lot of it before it harmed them. There is no immediate health risk to others.
The government has also ordered people living in Fukushima not to eat 11 types of green leafy vegetable grown locally that have been contaminated by radiation.
Local producers have been ordered not to send the goods to market, and in the neighbouring prefecture of Ibaraki they have been told to halt shipments of milk and parsley with immediate effect.
The Japanese Cabinet Secretary, Yukio Edano, said: "Even if these foods are temporarily eaten, there is no health hazard.
"But unfortunately, as the situation is expected to last for the long term, we are asking that shipments stop at an early stage, and it is desirable to avoid intake of the foods as much as possible."
He told a news conference that importers of Japanese foods should take a "logical stance".
Hong Kong has banned a variety of food imports.
The Food and Drug Administration in the US said that all milk and milk products and fresh fruits and vegetables from four Japanese prefectures - Fukushima, Ibaraki, Tochigi and Gunma - would be stopped from entering the United States.
Countries including China, Taiwan and South Korea have already been carrying out rigorous checks of Japanese food imports.
Setbacks
The confirmed death toll from the earthquake and tsunami has risen to 9,408, and more than 14,700 people are listed as missing.
An estimated half a million people have been made homeless and some 300,000 people remain in evacuation centres or temporary housing.
Japan has said it will cost as much as 25 trillion yen ($309bn; £189bn) to rebuild the country after the disaster.
Meanwhile, work has been halted at the Fukushima Daiichi plant after black smoke was seen rising from reactor 3.
Radiation levels were reported to be unusually high before the smoke was spotted; they later fell but remain higher than in recent days.
Engineers were earlier forced to halt testing of the electrical system at reactor 2 after radiation levels spiked. There is also concern about the rising temperature at reactor 1.
Power cables have been connected to all six reactors, and lighting has been restored at reactor 3.
The plant's operator, Tokyo Electric Power (Tepco), had hoped to try to power up water pumps to reactor 3 on Wednesday but it is unclear whether that will now happen.
Tepco has said restoring power to all the reactor units could take weeks or even months. Engineers' efforts have been frequently hampered by smoke and spikes in radiation.
On Tuesday, an International Atomic Energy Agency (IAEA) senior official, James Lyons, said he could not confirm that the damaged reactors were "totally intact" or if they were cracked and leaking radiation.
"We continue to see radiation coming from the site... and the question is where exactly is that coming from," Mr Lyons told a news conference.
The situation at Japan's quake-damaged nuclear plant remains very serious, the head of the UN nuclear watchdog said.
But IAEA director-general Yukiya Amano said he had "no doubt that this crisis will be effectively overcome".
Workers at the Fukushima Daiichi plant have been battling to cool reactors and spent fuel ponds to avoid a large-scale release of radiation.
Meanwhile, the death toll from the quake and tsunami has risen to 8,450, with nearly 13,000 people missing.
'Positive developments'
The Fukushima plant was crippled by fire and explosions after the 11 March quake and tsunami.
Electricity has been restored to three of six reactors and engineers hope to test water pumps soon.
Earlier, some workers were temporarily evacuated from the complex after grey smoke was seen rising from the No 3 reactor.
Reports said the smoke appeared to have come from a pool where the reactor's spent fuel rods were kept.
Radiation levels did not appear to have risen significantly though after the smoke was spotted, the IAEA and Japan's nuclear safety agency said.
White smoke was later seen rising from the No 2 reactor.
"The crisis has still not been resolved and the situation at the [plant] remains very serious," Mr Amano, the head of the IAEA, told an emergency board meeting.
But he said he was starting to see positive developments; the cooling system had been restored to reactors 5 and 6, and they "are no longer an immediate concern".
The US Nuclear Regulatory Commission - whose staffs are in Tokyo conferring with the Japanese government and industry officials - said the Japanese nuclear crisis appeared to be stabilising.
The NRC said that reactors 1, 2 and 3 had some core damage but their containment was not currently breached.
Meanwhile, the government has ordered a halt to some food shipments from four prefectures around the Fukushima nuclear plant, as concern increases about radioactive traces in vegetables and water supplies.
Villagers living near the plant have been told not to drink tap water because of higher levels of radioactive iodine.
The suspension - which the government said was just a precaution - applies to spinach from the prefectures of Fukushima, Ibaraki, Tochigi and Gunma, as well as milk from Fukushima.
Over the weekend spinach and milk produced near the nuclear plant was found to contain levels of radioactive iodine far higher than the legal limits.
However, senior government official Yukio Edano told a news conference that eating or drinking the contaminated food would not pose a health hazard. "I would like you to act calmly," he said.
The World Health Organization said it had no evidence of contaminated food reaching other countries. However, China, Taiwan and South Korea have announced plans to toughen checks of Japanese imports.
Bad weather forced Japanese Prime Minister Naoto Kan to cancel a planned visit to emergency workers near the Fukushima plant.
It is also making the recovery work a much more difficult task.
Search-and-relief efforts in the prefecture of Miyagi, where the police chief believes the final quake-tsunami death toll could reach 15,000, have been delayed by driving rain.
"We basically cannot operate helicopters in the rain," Miyagi official Kiyohiro Tokairin said.
"We have been using helicopters to deliver relief goods to some places but for today we have to switch the delivery to places that we can reach by road," he said.
Japan Nikkei climbs and yen weakens on G7 intervention
Japanese shares have climbed and the yen weakened after finance ministers from the G7 group of the world's richest countries agreed to step into the currency market.
The Nikkei 225 stock index rose 2.7% to 9,205.67, while the yen weakened against the US dollar to 81.21.
The yen hit a post-World War II high of 76.25 yen earlier this week, raising concerns about Japan's recovery.
Analysts said markets will remain volatile.
Also on Friday, the Bank of Japan said it would pump another 3tn yen ($38bn; £24bn) into the financial system, bringing the total cash injected by the bank this week to 37tn yen.
Big falls
Exporters gained the most from the G7's move, as a weaker yen makes their products cheaper to customers overseas.
Semiconductor manufacturer Tokyo Electron rose 3.4%, while electronics group TDK was up 3%.
Last Updated at 18 Mar 2011, 05:00 GMT*Chart shows local time
$1 buys
change
The Nikkei has seen some of its most volatile trading in the past week.
The index fell more than 16% over Monday and Tuesday, its biggest two-day fall for 23 years, before rebounding on Wednesday.
However, concerns about the strength of the yen pushed the index lower on Thursday.
"The main things investors are worried about now are the nuclear plant, impact of the earthquake and tsunami on firms and power cuts putting pressure on Japanese manufacturers," said Norihiro Fujito at Mitsubishi UFJ Morgan Stanley Securities in Tokyo.
However, following the decision by the G7 to intervene in the currency markets, the focus may now shift away from the yen.
Not least because there there are plenty of other concerns occupying investors, analysts said.
Japan tribute from Prince William at NZ quake memorial
Prince William has offered condolences to the people of Japan, while paying tribute to victims of last month's earthquake in New Zealand.
Prince William said: "Here today, we love and we grieve."
Speaking to a crowd of more that 30,000 people at a national memorial for quake victims in Christchurch he said: This community... can appreciate the full horror of what is unfolding in Japan."
The prince is on a tour of disaster zones in New Zealand and Australia.
He also saw the scene of a mine blast and will go on to flood-hit Australia.
Speaking at the memorial in Christchurch, in New Zealand's south island, he said the world had watched the city's resolute response to the disaster with awe and admiration.
He said the ordeal endured by residents of the city, New Zealand's second largest, gave them a unique insight into the situation facing Japan.
"Our thoughts and prayers are with them too," the prince told the memorial service.
New Zealand Prime Minister John Key also used the memorial to extend sympathies to Japan.
"Even today as we mourn here, we think of Japan's desperate plight," he said.
He said the images from the country brought "flooding back the raw emotional pain that accompanies such a devastating event".
The number confirmed killed during the magnitude 6.3 earthquake in Christchurch, on 22 February, stands at 166 but officials have said it is likely to rise to 182.
By Richard BlackEnvironment correspondent, BBC News
A satellite photo shows steam rising from the site around reactor buildings 1-4
Thursday's attempt to use helicopters to dump seawater on to the Fukushima power station is almost certainly unprecedented in more than half a century of nuclear power operations around the world.
Long-range video footage indicates why it is not a more widely-used technique: it does not appear to work.
Water cannon - tried, with similar results - seemed a similarly desperate measure.
Far more orthodox was the plan to reconnect the stricken facility back to the national grid, enabling the delivery of electrical power.
Although power stations' main job is to generate electricity, their grid connections flow both ways - the return leg meaning that everything at the site can keep working even if all its reactors shut down.
The connection supplying Fukushima was presumably swept away on Friday by the same wall of water that submerged its back-up on-site generators.
Early on Friday morning in Japan, authorities announced they had connected a cable from a functioning power line about 1km away.
That should allow technicians to re-start the main pumps - provided that the site's internal electrical circuitry and the pumps themselves have not been damaged by the earthquake, the tsunami or the series of gas explosions.
"It's clear that this is going to help significantly, because it'll allow them to start the pumps to re-circulate water both in the reactors and in the fuel ponds, because the water is constantly re-circulating," said Andrew Sherry, director of the Dalton Nuclear Institute at the University of Manchester.
Drying out
As the week progressed, the focus switched from reactors 1, 2 and 3 to the fuel storage pools, also known as cooling ponds, in reactor buildings 3 and 4.
Parts of reactor buildings 3 and 4, pictured during the helicopter mission, were severely damaged
They look like big, deep swimming pools, and are designed to store bundles of fuel rods - assemblies, as they are properly called.
Fuel assemblies are put in the pond when they come out of the reactor during its shut-down period.
If they are relatively new, they go back in the reactor again prior to start-up - if not, they may remain in the pond for months, even years, before going to a more long-term storage site and eventual re-processing.
At the time of the earthquake, reactors 4, 5 and 6 had been shut down for routine maintenance.
The tops of the rods are supposed to be about 5m (16ft) below the water surface. The water keeps them cool and prevents radiation.
In the absence of water, the temperature of the fuel can soar, increasing the chances of radioactive substances being released.
By Tuesday, it was clear that the pond in building 4 was short of water, for reasons that have not been completely explained; and on Wednesday, the US Nuclear Regulatory Commission (NRC), which has a team of 11 experts advising in Japan, said it was completely dry.
The International Atomic Energy Agency (IAEA) released data showing that on Tuesday and Wednesday, the temperature in pond 4 was 84C - way above normal, and about 25C higher than the equivalent ponds in buildings 5 and 6.
Thursday's entry for building 4 reads: "no data" - possibly because instruments monitoring the pond had been destroyed by heat.
Critical Issue
It appeared that cladding around some of the fuel rods had been damaged - possibly by fire.
What made the situation concerning the fuel pond in building 4 seem particularly serious was Wednesday's statement from Tepco saying: "The possibility of re-criticality is not zero".
The helicopters' water-lifting gear is more commonly deployed on forest fires
This meant that in the company's view, it was possible that enough fissile uranium was present in the cooling pond in enough density to form a critical mass.
In other words, a nuclear fission chain reaction could start in a pond that lies outside parts of the building designed to contain radioactive materials.
This raised the issue of just how much fuel was stored in the pond, how densely it was packed, and what precautions were being taken to absorb neutrons, the particles that sustain a chain reaction.
Some clues are contained in a presentation given by an employee of the Tokyo Electric Power Company (Tepco), which runs the power station, at a conference on fuel storage last November.
It confirms that the cooling ponds had been "re-racked" - in other words, they were storing more fuel assemblies than allowed for in the original design.
This is neither uncommon nor unsafe, provided the assemblies are properly spaced - although it may mean that additional measures are needed to absorb neutrons and prevent criticality, such as the use of solid boron sheets or the addition of boric acid to the water.
The presentation shows an abundance of spent fuel rods at the plant, taking up 84% of the available space in the various storage facilities.
The dry storage facility was completely full, while a big cooling pool away from the reactors contained 6,291 fuel assemblies - the maximum allowed being 6,840.
This left a further 3,450 assemblies distributed between the pools in the six reactor buildings.
How they were distributed is not known.
But the pools in buildings 4, 5 and 6 may have been very full at the time of the earthquake, given that any older stored rods would have been supplemented by those taken from the reactors for maintenance.
If "re-criticality" did materialise, it would lead to the enhanced and sustained release of radioactive materials - though not to a nuclear explosion - with nothing to stop the radioactive particles escaping.
Wind factor
Anyway - when the helicopters eventually flew in, after a day's delay, building 4 appeared to be the likely target.
An earthquake off the north-east coast of Japan puts the region on high alert, but a tsunami warning is lifted after 90 minutes.
