新島・式根島・神津島の変動はなぜ時間変化するのか?ー2000年三宅島噴火に伴う地殻変動ー
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概要
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Displacement velocities of the Niijima, Shikinejima, and Koudushima islands to Minamiizu from June to August in 2000 measured by the GEONET vary over time. It seems that the displacement velocities of the Shikinejima and Niijima islands show a reverse correlation. This can be explained by two pairs of dyke and fault plane, the northern and southern pairs. It is inferred from seismic activity that these pairs alternately became active. The displacement velocity of the Shikinejima was large when the southern pair was active, while that of the Niijima was large when the northern pair was active. Further, all of the displacement velocities became small for a few days after a large earthquake (M>6) occurred. This might be explained by a decrease in volumetric strain in and around the magma chambers in the lower crust.