屈折法地震探査によって見いだされた地殻中間層ー地震学的性質と温度分布ー

概要

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From results of deep seismic profiling conducted by RGES (Research group for explosion seismology) in the past decade, we found intermediate crustal layers with P-wave velocity of 6.3-6.4 km/s, between upper and lower crustal layers. The intermediate layers (ICL) lie just beneath the volcanic front of Hokkaido, Tohoku, and Northern Kanto. The record sections of the wide-angle reflections show that the ICL seems to have a reflective structure, but reflectivity is not as strong as that of the lower crust. The temperature of the upper surface of the ICL was estimated from geothermal gradient data compiled by Japan Geological Survey of Japan. We found that the temperature of the upper surface of the ICL is about 500℃, which is almost the same as that of the lower crust. The intermediate layer was not found beneath non-volcanic western Honshu. We interpreted this to mean that the intermediate layer is composed of transient materials in which mafic materials change into felsic materials due to magma and hydrothermal processes. By discovering ICL, more substantial problems related to the formation and the development of the island arc crust may be suggested.
東京大学の論文