1964 年 12 月∿1965 年 2 月の伊豆大島付近の群発地震 : 地震と噴火の関係

概要

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A remarkable seismic activity took place during the period from December 1964 to February 1965, near Oshima, one of the Izu Islands, south off Honshu, Japan. This seismic activity had three distinct stages. The first stage from 9 to 13 December, 1964, is of foreshock-mainshock-aftershock type in which the main shock is of magnitude 5.8. The second stage from 25 to 31 December 1964, is of swarm type, which includes three large shocks of magnitudes 5.2, 5.3 and 5.5. The third stage on 20 February, 1965, is of typical swarm type containing eight shocks of magnitudes larger than 4.0, of which the largest one is of magnitude 4.8. Volcanic tremors began to occur on 27 December, 1964, and the Volcano Mihara-yama had eruptions intermittently from 29 December, 1964, to 7 January, 1965. No intrinsic relation between seismic activity and volcanic eruptions is recognized in the present case, though a model implying indirect relation had been offered by Dr. K. Nakamura. Generally speaking, there is no significant correlation between volcanic eruptions of Mihara-yama and seismic activity near Oshima.
1975-05-01