"Spatio-temporal Gravity Variation During the 2000 Volcanic Activity of the Miyakejima Volcano, Japan (2)"

presented by the ERI Gravity Group: Shuhei Okubo (okubo@eri.u-tokyo.ac.jp), Masato Furuya, Sun Wenke, Yoshiyuki Tanaka, Hidefumi Watanabe, Jun Oikawa, Tokumitsu Maekawa

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The figures below show gravity change as of Sept. 4, 2000 since June 1998 and since July 6, 2000. Gravity decrease expected around the summit(center) cannot be verified because danger to human life prevents access to the observation point. Most spectacular in the figures is the butterfly pattern with a symmetry axis stretching from the center to the southwest of the island. It suggests the closing of a dyke below the axis, which supports the idea of sucking the magma beneath the island. In addition, the tensile closing offers adequate explanation why crustal movement is larger in the southern part than in the northern (refer to the GPS analysis).

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"From a Vacuum Cleaner to a Butterfly : Interpretation"

・ We proposed a vacuum cleaner model in the previous issue to explain the ever growing caldera collapse without significant mass ejection. The model naturally predicts closing of a dyke, if it does exist. More rigorous analysis based on the dislocation theory is now under way.

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