2021 年 9 巻 1 号 p. 113-124
Wigner and Choi-Williams distributions produce increased time-frequency resolution and are applied to obtain the time-frequency distributions for tsunamis. In this study, a chirp signal was analyzed to examine the performance of the Wigner distribution. The Choi-Williams distribution, which suppresses the cross terms, was applied to estimate the time-frequency distributions for tsunamis. The distribution for the tsunami waveform observed at Susaki, Kochi Prefecture showed that variations in the natural time periods at Susaki Bay were predominant and the maximum peak of the time-varying spectrum appeared about 80 minutes after the first tsunami wave arrived. The decay relation of the tsunamis was theoretically estimated using a wave energy equation with the rate of dissipation due to bottom friction and turbulence. A Talbot formula was obtained as the relationship of tsunami decay with time and its applicability was verified.
