海底設置用長波計による大船渡湾の静振観測結果について
1966 年 22 巻 1 号 p. 7-16
詳細
1966 年 22 巻 1 号 p. 7-16
The long-wave recorders which can be installed on the sea bottom of the depth from 10 m to 40 m are developed. By using them, the observation of seiches was carried out in order to know the characteristics of the oscillation of Ofunato Bay, along the coast of which the Chilean Tsunami in 1960 gave severe damages. Four observation points were selected from bay head to bay mouth. The spectral analyses of the records were made for each observation points and the coherences and phase differences between the records obtained at the bay head and those at the other three points were calculated. In Ofunato Bay, two modes with period of 40 min. and 15 min. are predominant. The maximum amplitude of the seich of 40 min. mode occurs at the bay head and that of 15 min. mode occurs at the intermediate point of the bay. These tendencies correspond to the height distribution of the Chilean Tsunami in 1960 and that of the Sanriku Tsunami in 1933, respectively. The observed amplitude distribution of the seiche of 40 min. mode shows good agreement with the calculated distribution, but that of 15 min. mode does not show good agreement. It seems that the ratio of the spectral density of 15 min. mode to that of 40 min. mode increases with increase of the wind velocity.
