Analysis and Verification of the 2011 Tohoku Earthquake Tsunami at Nuclear Power Plant Sites

Abstract

The tsunami caused by the 2011 Tohoku earthquake resulted in a severe accident at the Fukushima Daiichi nuclear power plant (NPP). In light of analysis of the generation mechanisms of the earthquake and tsunami, a tsunami source model is inferred and further verified by the seismic source model inferred from ground motions. Distribution of large slip in the area along the Japan trench is a common finding obtained from both models. Through simulation analysis of the observed tsunami at the NPP sites, it becomes clear that the large slip in the shallow area along the Japan Trench, the time difference of rupture propagation, and the time delay of tsunami propagation are the main factors that significantly affect the tsunami heights.

The Characterizing Model for Tsunami Source Regarding the Inter-Plate Earthquake Tsunami

“…As stated earlier, Sugino et al 8) proposed a TSM R of the Tohoku Earthquake Tsunami. While TSM R and TSM P are intrinsically different from each other, they are both tested and evaluated for reproducibility of past tsunamis.…”

“…Sugino et al 8) performed an inversion analysis based on these observation data and proposed a TSM R of tsunami waveforms observed by GPS wave gauges and the trace heights of four nuclear power plants including the Fukushima Daiichi Nuclear Power Plant. In addition, the Cabinet Office 12) , Imamura et al 13) , Fujii et al 14) , and Satake et al 15) also proposed TSM R of the same tsunami.…”

“…Analyses of the Tohoku Earthquake Tsunami, however, revealed that the large source area made it impossible to ignore the effect of these parameters. 8) As shown in Table 2 by the wave source models for the reproduction of the Tohoku Earthquake Tsunami, several models reflecting such a dynamic rupture effect have been proposed. For these models, from the rupture propagation velocity obtained by dividing the distance of the rupture starting point to the center point of each sub-fault by the time required until each sub-fault starts to slip, the average rupture propagation velocity is calculated to be approximately 1.5 to 2.0 km/s.…”

“…Note, however, that because the characterized tsunami The present purpose is, however, validation based on the Tohoku Earthquake Tsunami. Hence, it is premised that the area and location of the tsunami source for the characterized model are handled as known information, similarly to the case with the tsunami source model of Sugino et al 8) for the reproduction of the Tohoku Earthquake Tsunami.…”

“…As part of the effort to identify the cause of the Fukushima Daiichi Nuclear Power Plant Accident, Sugino et al 8) investigated the occurrence mechanism of the Tohoku Earthquake Tsunami to help improve the safety of future nuclear power plants. Their main achievements include: (a) creation of tsunami source models for simultaneously simulating the tsunami at the four tsunami-damaged nuclear power plants, and an estimation of the consequent slip distribution; (b) clarification of the fact that the dominant regions strongly influential on the tsunami levels for the nuclear power plants all concentrate in "the tsunami earthquake" occurrence area near the Japan Trench in the entire tsunami source area; and (c) the discovery of the fact that the earthquake source model estimated from the observed long-period earthquake ground motions agrees with the tsunami source above in that large slips concentrate near the Japan Trench.…”