The wave that washed over the eastern coast of Japan was more than 130 feet high.

You would expect that a disaster of the magnitude of the Tohoku tsunami and earthquake, which killed 15,000 people and caused about $210 billion in property damage, would have people feeling more apt to evacuate when another killer wave approaches. But, strikingly, scientists who interviewed Japanese people a year before the event and afterwards found that the size of the waves they would think dangerous enough to flee had grown. As Adam Mann writes at Wired, people had stopped recognizing the height at which a wave becomes dangerous:

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Reactor 3 at the Fukushima Daiichi plant, on March 24

What’s the News: A non-peer-reviewed study (pdf) publicized last week by radioactivity-detection expert Ferenc Dalnoki-Veress suggests that nuclear fission reactions continued at Japan’s Fukushima nuclear power station well after the plant’s operators had allegedly shut down the reactors there. The paper says there may be what are called “localized criticalities” have occurred in the plutonium and uranium left in the reactors—little pockets of fuel that have gone critical, propagating the nuclear chain reaction and generating potentially harmful radiation. The existence of criticalities is controversial: some researchers say there are certainly none; Dalnoki-Veress himself says it’s only a possibility.

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Update (March 15): Shortly after this post was originally published, the situation at the Fukushima Daiichi facility worsened dramatically: there was an explosion at a third reactor, which may have damaged the containment unit there, along with a new fire. Reports elsewhere now suggests that more radioactive material escaped, but the extent of the risk of further release of radioactivity is not yet clear. The title of the post has been edited to reflect the changing situation. (Original title: “Relax: Fears Of Japan’s Radioactive Leakage Are Overblown”)

A  second explosion hit Japan’s Fukushima Daiichi nuclear power plant today and authorities are preparing to pump seawater into a third imperiled reactor. But considering that Friday’s earthquake was seven times more powerful than the maximum limit they were designed to withstand, we’re lucky the situation isn’t much worse. Japan’s scenario is a far cry from Chernobyl: Any radioactive leakage that has occurred is low, and unlikely to affect anyone outside the local area (if that).

What Happened

Both today’s explosion (in reactor No. 3) and the one on Saturday (reactor No. 1) have the same cause: a breakdown in the cooling system as tsunami waters swamped generators. Specifically, today’s explosion was caused by hydrogen gas, which builds up as the seawater that’s pumped in to cool the reactor also heats up. From video footage, the explosion looks devastating, and while 11 people were injured, the steel and concrete containment shell around the nuclear reactor was not damaged—which is the main reason why authorities say the situation is mostly under control. “There is no massive radioactive leakage,” Cabinet Chief Cabinet Secretary Yukio Edano told the New York Times. Here’s a rundown on the risks in the leakage that has occurred:

What Is Escaping (and How)?

The root problem is heat: Even though the nuclear chain reaction is safely stopped in all of Japan’s nuclear reactors, that doesn’t stop heat from building up.

The uranium “stopped” the chain reaction. But a number of intermediate radioactive elements are created by the uranium during its fission process, most notably Cesium and Iodine isotopes, i.e. radioactive versions of these elements that will eventually split up into smaller atoms and not be radioactive anymore. Those elements keep decaying and producing heat. Because they are not regenerated any longer from the uranium (the uranium stopped decaying after the moderator rods were put in), they get less and less, and so the core cools down over a matter of days, until those intermediate radioactive elements are used up. [The Energy Collective]

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Oil refineries aflame. Train tracks twisted like string. Buildings ripped from their foundations. Japan’s 8.9-magnitude earthquake has left its mark, especially in the expected death toll of over 1,000 people. This video roundup shows the science behind what happened today in Japan.

Why (Most) Buildings Didn’t Crumble

The death toll is estimated around 1,000, which is bad enough, but it would have been much higher without good engineering, mandated by strict building codes. But these codes haven’t been strict for long. In the 7.3-magnitude Kobe earthquake in 1995, 6,500 Japanese people died, and engineers looked on in horror as many buildings came crashing down; the most deadly ones were built before 1981, when building standards were still lower.

The Kobe tragedy, says The Telegraph‘s Peter Foster, compelled Japanese officials to tighten building regulations for residential offices and transportation infrastructure. Engineers made buildings  “earthquake proof” by outfitting them with “deep foundation and massive shock absorbers that dampen seismic energy,” and by enabling the bases of buildings to move “semi-independently to its superstructure, reducing the shaking caused by a quake.” Skyscrapers now sway during an earthquake but don’t collapse, Foster says, and that helps explain why damage to buildings in Tokyo was kept to a minimum this time around. [The Atlantic Wire]

Why Couldn’t Geologists Predict It?

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Japan’s massive earthquake today may be over, but we’re still feeling the effects, from nuclear reactor scares in Japan to tsunami warnings along the entire west coast of North America, from Mexico to Alaska’s Aleutian Islands. Much is still unknown about this earthquake, including official destruction assessments and total death tolls, but here’s what we do know:

Two preliminary earthquakes with magnitudes of 7.2 and 6.3  struck off the coast of Honshu, Japan, the day before the major blow: This 8.9-magnitude quake—the largest in Japan’s recorded history—struck at 2:46 pm local time on Friday, its epicenter located about 231 miles northeast of Tokyo at a depth of 15 miles. Even after this large one, over thirty aftershocks—the strongest measuring 7.1 in magnitude—continued to batter the island nation.

The Immediate Effects

Fires and collapsed buildings were the main cause of injuries and death early on, from conflagrations sweeping an oil refinery in Chiba prefecture near Tokyo to the roof collapsing during a graduation ceremony in Tokyo. But fears soon centered on Japan’s nuclear facilities: Four power plants successfully shut down, but one experienced problems:

According to Nature’s Tokyo correspondent, David Cyranoski, Japanese media are reporting that the emergency core cooling system (ECCS) at the Fukushima #1 plant is not working due to a loss of electrical power, and problems with the backup diesel generator. The reactor is currently relying on an alternate cooling system that circulates water using a pump system. This system can operate for about 7 to 8 hours. According to the Nuclear and Industrial Safety Agency of the government’s industry ministry, this is the first time in Japan that the ECCS of a nuclear power station has not functioned. [Nature]

The local governments near the Fukushima plant urged the area’s 2,000 residents to evacuate, though no leaks have been detected and the Japan Atomic Industrial Forum assured everyone (pdf) that Fukushima reactor’s core “still has a sufficient amount of water for cooling, with no danger of the nuclear fuel being exposed”.

Why It Could Have Been Worse

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