古地磁気方位・強度測定による桜島の溶岩流の年代推定

概要

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A paleomagnetic study was carried out on four historic and three pre-historic lava flows at Sakurajima volcano, Kyushu, Japan. Measured directions of natural remanent magnetizations and paleointensities indicated good concentration for each lava flow with a few exceptions. The directions and paleointensities from historic lava flows are concordant with those expected from known geomagnetic secular variation in Japan. This suggests that they correctly reflect the ancient geomagnetic field and such comparison is applicable for the age estimation. The Nagasakibana, Kamonzaki, and Miyamoto lava flows were paleomagnetically corresponded to the late 8th century, about 3 ka, and about 4 ka, respectively. These ages are consistent with lava stratigraphy. The paleointensity determination combined with directional measurement was much helpful to reduce possible candidates of those erupted ages.
1999-06-30