Insights into the ground motion records of the Honshu (Japan) earthquake of 11 March 2011
This paper is a follow-up of a preliminary report on the same subject, which was posted on the website of this Journal on 25 March 2011. The report investigated the ground motion records of the Honshu earthquake of 11 March 2011, made available by the Japanese accelerometric networks KIK-NET and K-NET and by an Italian seismometric network, operated by the CERI Research Centre (Sapienza University of Rome) and located in the central Apennines. The paper highlights some kinematic and spectral features identified in the above records after analysing them in the time and frequency domains. Possible amplification effects due to the local geological setting also result from a preliminary analysis of the ratios of local ground motion to bedrock motion. The comparison of the distribution of these effects with the location of the main nuclear power plants (NPPs) of the Honshu island shows that: i) local seismic amplification was not particularly significant in these sites, and ii) the response spectra of the Honshu earthquake did not exceed the design spectra of the NPPs located along the eastern coast of Honshu. Finally, a preliminary analysis of the damages caused by the Honshu earthquake vs. previous seismic events which hit Japan and Italy in the last century indicates that the ratio of casualties to ex- posed inhabitants substantially dropped after the second world war (below 1% in both countries). Nevertheless, it is worth stressing that the latest two seismic events considered here (L’Aquila earthquake in 2009 and Honshu earthquake in 2011) had an almost equal ratio of casualties to exposed inhabitants, in spite of a difference of about 3 orders of magnitude.
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