1975 年 28 巻 4 号 p. 461-471
Adding mareographic data at the Kuril Islands, the source areas of the 1973 Nemuro-oki tsunami and the 2nd tsunami accompanying the largest aftershock on June 24, 1973 are reanalyzed. The result is the same as shown in the preliminary report: The source length of the 1973 Nemuro-oki tsunami is 130km long parallel to Nemuro Peninsula and the area is 7.2×103km2. The source length of the 2nd tsunami is 100km which is longer than the aftershock area reported by NOAA, and the western half of the source area seems to overlap with the source area of the first tsunami.
The 3rd tsunami of Sept. 27, 1974 was observed with small amplitude at Hanasaki. The estimated source area of this tsunami is within the source area of the 1973 tsunami. The 4th tsunami of June 10, 1975 was generated by an earthquake with the magnitude of about 7 (JMA), but the tsunami magnitude was relatively large. According to the author's method based on the attenuation of tsunami height with distance, the tsunami magnitude (Imamura-Iida scale) is m=1.5. This magnitude is the same grade to that of the 1973 Nemuro-oki tsunami. The estimated source area falls inside the source area of the 1969 Shikotan tsunami. The source length is about 100km long and its area is 6.3×103km2. The sea-bottom of this area may be uplifted, judging from the initial motion of the tsunami observed at Hokkaido and Sanriku.
The source areas of the tsunamis generated after the 1973 Nemuro-oki tsunami moved to the north-eastern direction along the continental slope. Within the source area of the 1969 Shikotan tsunami, many tsunami sources are located. On the contrary, there is a remarkable gap of the tsunami source area between the 1952 Tokachi-oki and the 1973 Nemuro-oki tsunamis. The source area of the 1973 tsunami occupies only the eastern half of the 1894 tsunami source. The area to the south-west of the 1973 tsunami may be considered a region of relatively high tsunami risk.