The few, seemingly miraculous, stories of survival are passed on from person to person, and some are given as much media coverage as the horrific devastation. The rescue of a 60-year-old man from the roof of his house, washed 15 km out to sea; the survival of a 4-month-old girl who was swept away from her family but later reunited with them; the safe birth of a baby by flashlight, in the cold, in a hospital with no power. These are stories we can understand, gain a morsel of sustenance from. The stories of the giant waves, the thousands of deaths, the bodies: these are too big to comprehend.

Sixteen years ago, the last time Japan was struck by a really big quake, it was very different. When the magnitude 6.8 Great Hanshin Earthquake hit Hyogo Prefecture at 5:46 a.m. on Jan. 17, 1995, more than 6,000 people died, mainly in built-up areas, and especially in the city of Kobe.

That quake, originating 16 km underground and 20 km from Kobe, caused some ¥10 trillion of damage, amounting to 2.5 percent of Japan’s Gross Domestic Product. It was a type of tremor known as an inland shallow earthquake, which was caused by east-west movement along the Nojima fault in the vicinity of Awaji-shima in the eastern part of the Seto Inland Sea, whose largest island it is. On that occasion it was the shallowness of the event, rather than its brute seismic force, that exposed buildings to large amounts of energy and led to such serious damage.

Now fast-forward to March 11, 2011, at 2:46 p.m. Some 130 km off the coast of the Tohoku region of northeastern Japan, and 32 km deep, a magnitude 9.0 megathrust earthquake occurred. This is when two tectonic plates collide — not when “mere” faults shift — and one is forced under the other. In this case, the Pacific plate was forced beneath the Okhotsk plate. Megathrusts are the most violent forms of geological activity, and as we all know, the March 11 quake caused a huge, devastating tsunami.

In 1995, the Japanese government was criticized for its slow response to the disaster. Indeed, it was down to the country’s largest yakuza crime syndicate, the Kobe-based Yamaguchi-gumi, to provide much-needed initial aid to stricken citizens.

That lesson seems to have been learned. This time, the government quickly sent in members of the Self-Defense Forces after the disaster occurred. As I write, some 100,000 soldiers are trying to get much-needed food and water to survivors and evacuees, and the government has asked for — perhaps a little tardily — foreign aid.

In 1995, there was no megathrust quake, and no tsunami. Crucially, too, there was no damage to any of Japan’s 55 nuclear power stations, and the Japanese economy was in a much stronger state. On March 11, a tsunami up to 10 meters high traveled as far as 10 km inland, killing thousands and wiping whole towns and villages off the face of the earth. One estimate puts the direct economic hit at ¥16 trillion.

So what’s happened, and continues to happen, is what Katsuhiko Ishibashi, a seismologist at Kobe University, has termed a genpatsu-shinsai (nuclear power quake disaster). He’s been waiting for this to happen. Many have. Not from a ghoulish sense of horror, but from a simple knowledge of geology. In a country with 108 active volcanoes and so many nuclear power stations, it was only a matter of time before an earthquake and/or a tsunami hit in the wrong place.

Among the people I’ve spoken to in Tokyo, there is a sense of the unreal; there is fear, and rumor, but there is also a strong sense of unity. The government is counting on this. Emperor Akihito himself called for it, in an unprecedented televised address to the nation on Wednesday, March 16.

I watched the Emperor’s speech, and felt transported to a kind of Japan familiar from books by Yukio Mishima: a place so incredibly, heartbreakingly formal. However, I imagine that if the Queen of England addressed her nation in a time of extreme crisis, she would hardly adopt an informal tone.

Radiation is not yet a widespread problem, but there is confusion and suspicion about what is going on regarding this invisible presence in the air. As I was writing this, safe in London while the snow fell in Tohoku, a friend in Tokyo phoned me and asked where he could buy a Geiger counter. But another friend in Tokyo said she didn’t care about the radiation in Fukushima — it was the aftershocks that were stopping her sleeping that she cared about.

Though undoubtedly serious, the threat from the stricken Fukushima Daiichi (No. 1) plant operated by Tokyo Electric Power Co. (TEPCO) is nowhere near that posed by the Chernobyl disaster in Ukraine in April 1986. On that occasion, the nuclear power station’s graphite-cooled core itself exploded while in operation and burned for days, spewing large amounts of radioactive material high into the atmosphere, mixed in with carbon soot.

Prevailing winds at the time spread the grimy, radioactive cloud over many parts of Western Europe, as far away as northern England. As it happened, there was heavy rain as the cloud passed over upland areas in Wales and England’s scenic Lake District, and the radiation was taken up by grass, eaten by sheep and cows, and may have entered the food chain. Whole areas around Chernobyl were quarantined for years — some still are — and for many years after, the meat of upland Welsh sheep and ones from the Lake District, as well as milk from those areas’ cows, was not fit for human consumption.

Many scientists, including John Beddington, Chief Scientific Officer to the U.K. government, insist that a Chernobyl scenario can’t happen this time. They say that’s because the reactors at Fukushima are of a different type — they are cooled by water, not graphite — and they had been turned off already when the quake struck and before the tsunami hit.

This means that a Chernobyl-type explosive release of clouds of hot carbon ladened with radioactive materials simply can’t happen at Fukushima.

At Chernobyl, the pressure vessel containing the reactor core was breached, and the reactor had no containment structure. That was why, when the core exploded, it threw its lethal cargo into the atmosphere.

At the time of writing, it is not known whether the inner reactor vessel has been breached at Fukushima, although the relatively small amounts of radiation being released suggest not. In addition, the radioactive elements being released from the Fukushima plant are caesium-137 and iodine-131. Certainly, these can travel far afield — they have already been detected for days in Tokyo, some 250 km distant — but their volatility means that you can’t get a large dose of them blowing in the wind.

In large doses, radioactive iodine can be dangerous, especially to children, but if there is a risk of contamination, potassium iodine tablets can protect against it.

This is the science of what we know about the Fukushima disaster. It doesn’t say anything about whether the reactors were too old, or whether TEPCO, the plant’s operator, is at fault for not renovating them or already decommissioning them — though both charges have been made. And it is easy for me, on the other side of the globe, to urge calm when I’ve got no quakes or isotopes to worry about.

As TEPCO workers continue to labor heroically, remember this: There is no nuclear apocalypse looming. To use that word is almost an insult to the thousands of dead from the tsunami, and to the tens or hundreds of thousands who have lost their homes and loved ones.

The Emperor said: “I hope from the bottom of my heart that the people will, hand in hand, treat each other with compassion and overcome these difficult times.”

Let’s add this: I hope people use rationality to assess, as calmly as possible, the risks they face. And that will help the country through the crisis.

Rowan Hooper is the News Editor of New Scientist magazine, and a JT Nature page writer whose Natural Selections column appears on the second Sunday of every month. Follow him on Twitter @rowhoop.

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