Seismic structure of the old oceanic Pacific plate and its implications

Abstract

In the northwestern part of the oceanic Pacific plate off northeast Japan, JAMSTEC has conducted extensive controlled-source seismic surveys. The results of the structural analysis show that there is a good correlation between the thickness of the oceanic crust and the water depth there, suggesting the static isostacy. This means that a few hundred meters difference in water depth corresponds to a few tens of percent difference in the thickness of the oceanic crust, resulting from the formation process of the oceanic plate at the ancient spreading ridge axis. A petit-spot site was found in an area of thin crust, suggesting that the ancient scars caused at the spreading ridge axis may control current volcanic activity on the old oceanic plate.