Deep Structure of Seamount of Younger Age Inferred from Gravity Anomaly.

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概要

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• In the recent studies of the ridges in the Indian Ocean, it was found that the compensation depth of isostasy became shallow with mean ascending speed of about 1mm/year. "Bubble Model" and "Two Layers Model" were proposed. For the better understanding of the upward movement of low density material, we studied the relation between gravity anomaly and topography for the Hawaiian Ridge. The ridge has two topographic highs having different wave length: about 1, 700km and 350km. As for the topography of wave length of more than 1, 000km, calculated depth of compensation is about 80km. The depth is nearly the same with the depth of the boundary between lithosphere and asthenosphere given from difference between observed gravity anomaly and that calculated from the crustal velocity structure. On the other hand, the depth of compensation for the topography of wave length of about 350km is 40km, assuming Airy's isostasy. This gravity effect is equivalent to that of the structure at two different depths: 10km (depth to the Moho) and 80km, where the contribution of the Moho for the isostatic achievement is about 60% and the contribution of the deep boundary is 40%. The result coincides with the velocity structure below the Islands of Hawaii. Though the results are for the ridge or the seamount of hot spot origin, we suspect that the model can apply to the case of the formation of an island arc.

• 日本学士院の論文

著者

• Fujimoto Hiromi

  Ocean Research Institute University Of Tokyo

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