39.八丈島における海洋長周期波の解析

Long-period wave recorders were installed at Kaminato and Yaene, Hachijo Island. The observations at Yaene were carried out over a period of eight years in order to understand the characteristics of water level oscillations at an isolated island. According to spectral analyses, the seiche periods of 4 min and 5 min are always predominant in the fishing port at Kaminato. While features of wave spectra at Yaene are flat on ordinary days, predominant peaks are found in a band of periods of 5 min, 7 min and 10 min at the time of typhoons and cyclones. It is remarkable that long-period waves of more than 15 min are not significant at both stations. On the other hand, in cases of tsunamis, the predominant peaks of spectra fall in the band of long periods and its position moves to the low frequency part as earthquake magnitude increases.|宮城江ノ島と伊豆大島津波観測所の補助ステーションとして,1958年11月八丈島の神湊に携帯用長波計を据付け,長周期波の観測を行なってきた.しかし神湊では,常時4分と5分の漁港のセイシュが卓越していることが判り,観測は6ケ月間で中止した.一方,同島西部の八重根において,1959年3月より1967年12月まで同様な長周期波の観測を行ない,この間に1964年3月アラスカ津波と1965年2月アリューシャン津波を記録した