Bird’s Eye: What caused that earthquake? What exactly is going wrong in the nuclear power plants? Those answers don’t exist, but we offer the best of the many explanations we’ve seen this week. We start with the tectonic (or subduction) plates whose movement initiated the tsunami, and how that happened. Then we have a 3 minute video showing the succession of quakes over the last week. Then a BBC explanation of Fukushima, step by step, followed by a general overview of how much radiation is coming from the plant, compared to chest x-rays and more familiar experiences.

* Japan earthquake: The Explainer Scientific American

Japan is situated in a complicated plate boundary region where three subduction zones meet. Two of these subduction zones run parallel to the east coast of Japan. To the south, the Philippine plate is being subducted beneath the Eurasian plate, whilst to the north, the Pacific Plate is being subducted beneath the North American plate….With all of these tectonic plates jostling against each other, it is no surprise that Japan has a long history of catastrophic earthquakes….

Over the other side of the Pacific there are similar gaps in our knowledge, but we do know enough to understand that the real risk to the western US and Canada is not from tsunamis generated across the other side of the Pacific, but ones generated on this side. North of the San Andreas Fault, the plate boundary that runs along the west coast is a subduction zone very similar to the ones that run along the coast of Japan, and just as capable of generating large earthquakes. … There is no way to predict exactly when an earthquake will occur, but it is a 100% certainty that eventually the Cascadia subduction zone will rupture. The only question is over the willingness of the societies that live on top of it to face this tectonic inevitability.

* Japan Quake Map

A remarkable flash map running through all the earthquakes from the day before the 9.0 one to the present. Gives a full sense of how many major quakes there were on both sides of the big one.

* Japan quake: Power line laid to Fukushima nuclear plant BBC

An update from Thursday (with rare good news). But scroll to the bottom, where an excellent 12 panel explanation gives a complete and clear explanation of the nuclear plant, and what went so wrong in it.

* Potential Health Effects of Radiation Exposure Technology Review

The health effects of radiation depend on the dose a person receives. The acute effects of radiation sickness usually begin when an individual receives a dose of radiation that is one sievert (the standard international measurement of radiation exposure) or above. Most of the workers hospitalized after the nuclear disaster that destroyed a reactor in Chernobyl in 1986 received estimated doses of between one and six sieverts. Because such levels are rarely encountered, radiation levels are most often given in millisieverts (one thousandth of a sievert) or microsieverts (one-millionth of a sievert). For comparison, a chest x-ray delivers about 0.2 millisieverts of radiation, and the average person in the U.S. is exposed to about six millisieverts of radiation per year, about half of which is from natural sources and another half from medical procedures.

Radiation levels at the Fukushima plant have fluctuated widely. The highest emissions levels so far are 400 millisieverts per hour—rates that are high enough to cause symptoms of radiation sickness within two or three hours. But that level quickly dropped, and other readings have been far lower. On Tuesday, measurements at the gate of the power plant ranged from 0.6 millisieverts per hour to 11.9 millisieverts per hour, according to the International Atomic Energy Agency. The levels at the gate were at 1.9 millisieverts per hour on Wednesday, according to the Japan Atomic Industrial Forum. Radiation levels, however, are changing rapidly, and there have been reports of rapidly rising levels due to problems with stored spent fuel rods.