5. Tsunami Sources in Hokkaido and Southern Kuril Regions

Adding new data of tsunamis which were observed at tide stations of Japan and USSR during the last 76 years (1894～1969), the characteristics of tsunami sources in the Kuril region are investigated. The estimated tsunami sources are located on the steep continental slope near the ocean trench and agree approximately with the aftershock areas reported by the USSR sources. According to the statistical formula (Iida, 1958), the source dimensions of tsunamis in this region generated by shallow earthquakes (d<30km) are of the standard size. Judging from the initial motion of the tsunami observed by tide gauges, the shoreward sea bottoms in the tsunami source areas are upheaved in most cases. The peaks of tsunami spectra are in the range of 16～35 min and the peak period is longer for the larger tsunami magnitude. From the tide gauge records in Hokkaido, the possibility of tsunami generation in this region is uncertain for the earthquakes in the magnitude range M=5.9 to 6.7.|戦後,南千島に起きた津波は,Solovievを中心とするソ連の研究者により,精力的な調査研究が行なわれてきた.1958年エトロフ沖,1963年ウルップ沖の津波のほかに,多数の微小津波が報告された.今回,1894年釧路沖津波,1918年ウルップ沖の歴史的津波をはじめ,北海道の検潮記録とソ連の報告をもとに,逆伝播図の方法から,これら微小津波の波源域を推定する.以上の結果を加えて76年間(1894～1969),南千島沖における波源の大きさと地理的分布の特徴を調べた