The massive rumbling energy released in an earthquake is from built-up stress within the Earth’s crust. Aftershocks aside, one might expect that such a release would let grinding tectonic plates chill out for awhile. Unfortunately, at the Fukushima Daiichi nuclear plant, seismic risk has increased since last March’s magnitude 9 earthquake. According to a report published in geoscience journal Solid Earth, the massive quake actually reactivated a seismic fault near the plant.“There are a few active faults in the nuclear power plant area, and our results show the existence of similar structural anomalies under both the Iwaki and the Fukushima Daiichi areas," team leader Dapeng Zhao, geophysics professor at Japan’s Tohoku University, said. "Given that a large earthquake occurred in Iwaki not long ago, we think it is possible for a similarly strong earthquake to happen in Fukushima,”The magnitude 7 Iwaki aftershock happened April 11, 2011, a month after the main quake. It happened just 60 kilometers away from Fukushima, while the main epicenter was 160 km from the plant. According to the study, if a new earthquake occurs, it will likely be much closer to the plant.Zhao’s team found that the Iwaki quake was caused by fluids being pushed up by the subducting Pacific plate. Those fluids act like a lubricant between a pair of grinding tectonic plates, and thus can alter the properties of faults. This can lead to a cascade effect, where one shift increases pressure on another area of the fault, which pushes it past the breaking point, potentially causing the cycle to repeat. That’s what happened in Iwaki, where more than 24,000 tremors were recorded between March and October 2011, as compared to just 1,300 total in the nine previous years.“Ascending fluids can reduce the friction of part of an active fault and so trigger it to cause a large earthquake," lead author Ping Tong said. "This, together with the stress variations caused by the 11 March event, is what set off the Iwaki tremor.”It almost feels like an ‘ignorance is bliss’ moment. Even as Japan struggles to deal with the aftermath of one of the worst nuclear disasters in history – not to mention an unbelievably devastating natural disaster – here’s the terrible news that the tremors might not be over. But as the country continues with cleanup operations that may take 20 years, it’s extremely important to have an idea of what’s to come. So while decontamination efforts are key, this study would suggest that the most important task in the near future is to make sure the plant’s reactors – which are still leaking low-level radiation – are locked down and as secure as possible.
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