2020 Volume 20 Issue 4 Pages 4_1-4_17
The tsunami source models of the 2011 Tohoku Earthquake, which reproduce the wave gauge record offshore the Fukushima Daiichi Nuclear Power Plant, were obtained by the joint inversion of tsunami waveform data, 1-second sampling GPS data, and sea bottom crustal deformation data. For improving the reproducibility of the wave gauge record, we used an approach that includes a “hypothetical tsunami waveform” data in the joint inversion. The hypothetical tsunami waveforms were defined at the depth of 50 m offshore the Fukushima Daiichi Nuclear Power Plant,. The tsunami waves at the position of the wave gauge were simulated based on nonlinear long-wave theory using the tsunami source models obtained by the joint inversion including the hypothetical tsunami waveforms. The final modified hypothetical tsunami waveform, which minimized the sum of squared residuals between observed and calculated tsunami waves at the position of wave gauge, was searched among many hypothetical tsunami waveforms. By including the modified hypothetical tsunami waveform in the joint inversion, we obtained the tsunami source models reproducing the wave gauge record well. A similar approach using the hypothetical tsunami waveform data was also applied for improving the fit between the observed and calculated tsunami heights from Hokkaido to Chiba prefectures. It also became clear that the combined use of the 1-second sampling GPS data in the inversion is effective for constraining the characteristics of the fault rupture process.
