Analyses of Sub Moho boundary in Island-arc

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In Japan, the seismic structure has been obtained based on the earthquake prediction project. Recently, seismic studies using receiver function study were also done to declare the seismic structure beneath Japan. In the analyses, spatially high dense seismic array named Hi-net was used. The seismic images obtained from receiver function studies were compared with those of refraction studies. In southwestern Japan, the seismic images obtained from receiver function studies are consistent with those obtained from refraction studies. In the central part of Japan and northeastern parts of Japan, the seismic images of receiver function analyses are consistent with those of refraction studies. In addition to refraction Moho, a clear boundary was found which is 10 km deeper than refraction Moho, in the regions. This study suggested that existence of the sub-Moho boundary, which is 10 km deeper than refraction Moho boundary, in the central part of Japan and northeastern part of Japan. The boun … More dary was obtained from the comparison between the refraction survey and receiver function study. The characteristics of the regional variation of the sub-Moho boundary were researched. An interesting characteristic of the regional variation was found. The area that the sub-Moho boundary is located in the region that the active volcanoes are located. The seismic structure between the refraction Moho and sub-Moho was researched. A characteristic structure was found at the layer. The layer was characterized to be reflective. The scatter distributed model is suitable to explain the observed characteristics at the layer. In the continental region, the seismic structure of the crust and uppermost mantle has been studied. The seismic structure in the continental region was characterized with following structure which has transparent upper crust, reflective lower crust and transparent uppermost mantle. The seismic structure in Japan is different that of continental region. The uppermost mantle beneath Japan was not transparent. In this study, the formation process of the sub-Moho boundary was also studied. The seismic structure with sub-Moho boundary seems to be caused by the magmatic under plating. The sub-Moho boundary is the bottom of the magmatic under plating. Less