Study of Honshu Earthquake Aftershock Raises the Spectre of Future ‘Quakes at Fukushima

The Findings of the Iwaki Earthquake Study

Using a technique called seismic tomography, which identifies variations in density of the crust and mantle, the team concluded that the Iwaki earthquake was caused by fluids rising within the fault zone – a mechanism which can, by ‘lubricating’ the fault, cause earthquakes to occur.

Location of the 2011 M7.0 Iwaki  aftershock (image by USGS)

Location of the 2011 M7.0 Iwaki aftershock (image by USGS)

These fluids are generated by the process of subduction, in which one of the Earth’s crustal plates is forced downwards below another (the mechanism which generated the M9.0 earthquake). Heating of the subducted crust releases fluids which are forced upwards through fault zones, increasing the risk of earthquakes.

Potential Reactivation of the Fault Zone

Although Professor Zhao confirmed to Decoded Science that the Iwaki earthquake was the only significant aftershock close to Fukushima, it nonetheless raised cause for concern, occurring as it did in an area where recent earthquakes had been absent. In addition, a second, similar structural anomaly (indicating the possible presence of fluid) was identified under a second fault zone closer to Fukushima,

The study concluded that the reactivation of the fault zone which caused the Iwaki event and the possible presence of crustal fluids raise the prospect of a potentially devastating future event near to the Fukushima nuclear power plant. In the face of increased risk, the researchers recommended that ‘the security of the plant should be strengthened to withstand potential large earthquakes in the future.


United States Geological Survey. Latest Earthquakes M5.0+ in the World. Accessed February 16, 2012.

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Zhao, D. et al Tomography of the 2011 Iwaki Earthquake and Fukushima nuclear power plant area(2012). Solid Earth. Accessed February 16, 2012.

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© Copyright 2012 Jennifer Young, All rights Reserved. Written For: Decoded Science

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