The US Air Force is delivering a cargo of liquid coolant to the Tokyo Electric Power Company's Fukushima-Daiichi nuclear power plant - where one of six reactors seriously affected by today's quake is still alarmingly hot many hours after it was automatically shut down when the quake struck.
Electrical, mechanical and diesel generator failures are said to have combined to deprive the reactor of power for its coolant pumps.
The Tokyo Electric Power Co told Japanese news service Jiji News that pressure in the reactor vessel is rising and that the company intends to "take measures" to release it. CNN reports that activity around the plant hints at a "struggle" to cool down the facility. Indeed, Japan's trade minister said this evening that there could well be what he described as "small radiation leak" from the Fukushima plant.
US Secretary of State Hilary Clinton said local US air bases are helping deliver the coolant. The reactor - one of six - is thought to be a boiling water reactor, so the coolant is likely to be demineralised light water, meaning it is depleted of the hydrogen isotope deuterium.
Some 3000 local residents living within a 3 kilometre radius of the Fukushima plant have been evacuated by the Japanese defence force.
1722 GMT, 11 March 2011
Michael Reilly, senior technology editor
Seismologists at the US Geological Survey in Menlo Park, California, have just revised their calculations regarding the magnitude of today's quake. They now say it was magnitude 9.0. Already one of the top 10 recorded earthquakes in history, the revision suggests the quake was even more powerful than first thought.
Harold Tobin of the University of Wisconsin-Madison told New Scientist that this figure will probably change again. This is typical in the hours after a large seismic event, as more information becomes available.
Earlier today, it was suggested that the tremor may have occurred along a splay fault - a branch off the main megathrust fault which runs through this area of the Japan trench. If so, that could mean the fault was previously unknown to geologists.
Splay faults tend to break at steeper angles than megathrust quakes, making them highly likely to lead to a large uplift of the seafloor that produces damaging tsunamis such as the one that crashed ashore in Sendai and the Honshu coast earlier today.
But the new set of calculations indicate that the giant quake ruptured at an angle of 14 degrees below horizontal. Such a shallow slip suggests the earthquake did in fact occur along the main megathrust fault.
Tobin said that in the next few days, seismologists will be working feverishly to come up with a new set of calculations known as an "inversion" to determine over what area the fault slipped and how great the slip was. It's likely to have been several metres for an earthquake of this magnitude.
Once that's established, geologists will begin to look at how this earthquake may have transferred stress onto - or away from - faults in the Tokyo bay and Nankai trough regions, to the south-west.
This will help get a handle on the big question that will be on everyone's mind: when, and where, will it happen again?
(Image: Yasushi Kanno/AP/Press Association Images)
1514 GMT, 11 March 2011
Paul Marks, senior technology reporter
The Japanese government declared its first ever "state of nuclear emergency" today after two of its nuclear power stations suffered major failures in the aftermath of today's earthquake.
Quake damage cost one plant its reactor cooling system - an absolutely critical capability for a nuclear facility - while another suffered a fire in its turbine hall. Residents in a 3-kilometre radius of the coolant-afflicted plant have been evacuated.
Both incidents were considered risky enough to require the issuing of emergency alerts to the International Atomic Energy Authority in Vienna, Austria. However, the Japanese government insists this was precautionary and that no radiation release has occurred.
As the quake struck, seismic sensors triggered shutdowns at 15 of Japan's nuclear power stations. Eleven are thought to have resumed operation, but the four nearest the epicentre have remained shut - and the problems occurred at two of those.
After a nuclear plant is shut down, control rods are normally inserted into the reactor core to quench the fission reaction. But the reactor remains hot and still needs cooling.
At the Fukushima Daiichi nuclear power plant, located just to the south of the Miyagi district, which was worst hit by the quake and tsunami, electrical systems powering the plant's cooling system failed - and a backup diesel generator powering water pumps didn't cut in. The shut-down reactor remains hot.
"Japan's Nuclear and Industrial Safety Agency says the plant has been shut down and no release of radiation has been detected," said the IAEA in a statement.
Nearer the epicentre, the Onagawa nuclear plant in Miyagi was pictured with smoke streaming from its turbine building. While that's not a nuclear issue as such - it uses superheated steam to turn a generator - any incident near a reactor is bad news. The fire is now said to be out.
These failures will probably speed efforts to make Japan's nuclear plants more rugged against seismic risks - a process that was set in train after a July 2007 quake severely damaged Japan's Kashiwazaki-Kariwa nuclear plant in Niigata prefecture.
1305 GMT, 11 March 2011
(Image: AP/Press Association Images)
Michael Marshall, environment reporter
The Japanese earthquake has triggered a series of tsunami waves that are now moving east across the Pacific. How will the countries they hit be affected?
The shape of each landmass is a major factor determining how the tsunami behaves. Tsunamis are most dangerous when they run over a large area of shallow water. This causes the first wavefront to slow down, so successive waves pile up to form one tremendous wave.
As a result small Pacific islands, especially ones that lie in otherwise deep water, should be largely unaffected. Wave height here might reach 30 centimetres at most. "A little atoll presents a pencil in the water, and the wave just goes right past," says Robert Cessaro, a senior geophysicist at the Pacific Tsunami Warning Center (PTWC) in Hawaii. Because most of the islands in the tsunami's path are fairly small, they should see waves 10 to 30 centimetres high at most.
Islands with a diameter of 80 kilometres, including any underwater sediment surrounding them, will slow down the waves and thus experience a larger tsunami impact.
"It looks like the Hawaiian islands will see [waves] between 1 and 2 metres [in height], depending on where you are," Cessaro says. The first wave is expected in Hawaii at 1707 GMT (0307 local time).
Most of the tsunami's force seems to be heading for the west coast of North America, which could see waves of up to 40 centimetres in some areas. California will see the highest waves, with Alaska "pretty much out of the beam", says Cessaro.
California's Crescent City, which is susceptible to tsunamis because of its confined bay, could get up to 1 metre. Residents have been urged to move to higher ground.
South America is expected to see less of an effect than North America. Waves with a height of roughly 20 to 30 centimetres may occur here.
Cessaro emphasises that these figures are rough. Data on the tsunami is still coming in, and the PTWC will be updating their models throughout the day. As the wave moves on, more gauges will be affected, the measurements generated will feed into the models and the picture will become clearer.
1230 GMT, 11 March 2011
Catherine Brahic, environment news editor
(Image: NOAA)
The US National Oceanographical and Atmospheric Agency has produced this map showing when the tsunamis are expected to hit land across the Pacific. The quake was at 0546 GMT, meaning Hawaii could see the first waves around 1700 GMT (0300 local time) and smaller, low-lying Pacific islands like Tuvalu could be hit in the coming few hours.
The University of Southern California's Tsunami Research Centre also has this map showing the theoretical path of a tsunami, with maximum wave heights. The map is not a forecast for today's events, but the results of modelling studies the centre has done in the past for a quake of similar location and magnitude.
1200 GMT, 11 March 2011
Andy Coghlan, reporter
Brian Baptie, a seismologist at the British Geological Survey in Edinburgh, UK, answers our questions on the Japan quake and related tsunamis, reported at 10 metres in Sendai port in Miyagi prefecture, north-eastern Japan.
Are the recent huge quakes linked?
This one is on the same scale as the Chile quake last year and the Sumatran quake in 2004, so there is a sequence that's been followed. They're all caused by motion of tectonic plates. There's no causal link between them, but it is possible that one quake could trigger another, so it's possible Sumatra has unleashed a chain of quakes and rupture segments to the west of Sumatra.
But it's not linked to the recent earthquake in Christchurch, New Zealand. This latest quake was 8000 times large than the Christchurch quake in terms of the energy released, so it's a different beast.
What was the geology of the quake?
Japan sites at the boundary between two tectonic plates - there are eight major plates worldwide. To the east of Japan is the Pacific plate, and Japan itself sits on the Eurasian plate. The Pacific plate is moving west at about 8 centimetres a year, and is pushing down beneath Japan itself. As the plates push past each other, a massive amount of strain energy is generated, which builds up in the rocks. Sometimes the strain can build for many years, and that's the underlying cause for earthquakes in Japan. The amplitude of the quake decreases rapidly from the epicentre, although it will be felt across all Japan.
What about the tsunamis now moving east?
They travel at the speed of a jet airliner and propagate at low amplitude deep in the ocean. As they approach land, the tsunami slows down but the amplitude increases, generating waves with huge energy. So you still get large waves several metres high many hours after the original quake. They can still cause extreme amounts of damage many kilometres away. Also, individual tsunamis can last for many waves, and sometimes the first is not the biggest.
Was Japan ready?
Japan is a country with a long history of earthquakes, but this one is unprecedented in Japanese history. The previous largest was Great Kanto in 1923, south of Tokyo, which resulted in 140,000 deaths, and that was 7.9 magnitude. That puts this latest one in perspective. It's easily the largest Japan has ever experienced.
Japan has well-regulated building codes, and large buildings are constructed not to collapse. Also, people are well prepared both for quakes and tsunamis, with regular evacuation drills. All those will have saved life this time.
Are Japan's nuclear facilities safe?
They're unlikely to collapse in a quake, but they will have experienced strong shaking. Reactors have their own earthquake warning system that shut them down automatically. These also work for high-speed rail networks. But it's difficult to say what damage there's been to these facilities.
1032 GMT, 11 March 2011
Wendy Zukerman, Asia-Pacific reporter
(Image: Kyodo News/AP/PA)
A massive 8.8-magnitude earthquake struck off the north-east coast of Japan today, creating a tsunami that hit the north of the country and sparking tsunami alerts around the Pacific.
According to the US Geological Survey (USGS), the quake hit at 0546 GMT, with its epicentre 373 kilometres north-east of Tokyo. Preliminary reports suggest it occurred at a depth of 24.4 kilometres.
Japan's Meteorological Agency says that movements in the crust caused by the quake created a tsunami that moved towards Japan's east coast, reportedly reaching a height of 10 metres at the point of impact.
Kevin McCue, a seismologist at Central Queensland University, Australia, says tsunami waves "will be impacting other countries in the north Pacific in the coming hours".
Already, the US National Oceanic and Atmospheric Administration's Pacific Tsunami Warning Center has issued a tsunami warning for many areas bordering the Pacific. The first wave is expected in Hawaii at 1707 GMT (0307 local time).
James Goff, a tsunami researcher at the University of New South Wales in Sydney, Australia, says that tsunamis are virtually inevitable given the power of the earthquake. "Japan has a rigorous earthquake building code and excellent tsunami warning system and evacuation plans - this event will likely provide a severe test for all of them," he says.
While details of the devastation in Japan remain murky, there have already been numerous reports of injuries, and five confirmed deaths. Power has been cut to 4 million homes in and around Tokyo. Five nuclear power plants in northern Japan have been shut down, but there are no reports of leaked chemicals.
Earthquakes are common in Japan because it is one of the most seismically active regions in the world. On 26 February the country experienced a 5.2-magnitude quake; a 7.2-magnitude quake hit just two days ago, and was followed by four more quakes yesterday. But quakes of a similar magnitude to today's are rare. It is similar in scale to the quake that hit Chile almost a year ago to the day.
"This is the largest earthquake known in Japan," says McCue. There have been just seven earthquakes in Japan over magnitude eight since 1891.
