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From article

Source article

Solid Earth

Published By

Dr. Dick van der Wateren

Tags

Earthquake, Tomography, Tsunami, Nuclear disaster, Fukushima


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Earthquakes still threaten Fukushima Daiichi nuclear plant

17.02.2012, Age: 2259 days

A new article in the open-access journal Solid Earth presents high-resolution tomographic images of the crust and upper mantle in the area around the Fukushima nuclear power plant, which has been seriously damaged during the M7 earthquake of 11 April 2011.

The research team, led by Dapeng Zhao, a geophysics professor at Tohoku University, stated this week: “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. 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 Fukushima Daiichi plant lies on crust with similar structures as the crust under Iwaki, where the earthquake occurred. The paper notes that the seismicity near the plant is relatively low compared to that near Iwaki, but says the ascending fluids can still be a threat. A fault line that runs close to the plant could be weakened by these fluids.

Abstract

High-resolution tomographic images of the crust and upper mantle in and around the area of the 2011 Iwaki earthquake (M 7.0) and the Fukushima nuclear power plant are determined by inverting a large number of high-quality arrival times with both the finite-frequency and ray tomography methods. The Iwaki earthquake and its aftershocks mainly occurred in a boundary zone with strong variations in seismic velocity and Poisson's ratio. Prominent low-velocity and high Poisson's ratio zones are revealed under the Iwaki source area and the Fukushima nuclear power plant, which may reflect fluids released from the dehydration of the subducting Pacific slab under Northeast Japan. The 2011 Tohoku-oki earthquake (Mw 9.0) caused static stress transfer in the overriding Okhotsk plate, resulting in the seismicity in the Iwaki source area that significantly increased immediately following the Tohoku-oki mainshock. Our results suggest that the Iwaki earthquake was triggered by the ascending fluids from the Pacific slab dehydration and the stress variation induced by the Tohoku-oki mainshock. The similar structures under the Iwaki source area and the Fukushima nuclear power plant suggest that the security of the nuclear power plant site should be strengthened to withstand potential large earthquakes in the future.


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