1974年伊豆半島沖地震の余震観測報告 : 新島観測点

概要

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1974年伊豆半島沖地震調査概報An earthquake occurred at the southern tip of the Izu Peninsula on May 9th in 1974. A large fault, running in a NW direction along the south coast line of the Izu Peninsula, appeared at Irozaki, in the southern tip of the Izu Peninsula. Aftershock observation was carried out at Nil-jima Island, which is SE off the IzuPeninsula. Many aftershocks and many earthquakes near Nil-jima were observed. The former occurred in two active regions, that is, one along the fault and another near Mt. Amagi. These two regions are separated from each other. The activity near Mt. Amagi was similar to a swarm type. The activity near Nil-jima caused eight noticeable shocks. The period of greatest acti- vity was almost simultaneous for Mt. Amagi and areas near Nil-jima. Many disastrous earthquakes have occurred near Nil-jima, Kozu-jima and Miyake-jima during the past 85 years. These were also of a swarm type.