地震波トモグラフィーから見た地球内部の物質循環

抄録

Whole-mantle 3-D P-wave velocity (Vp) structure under West Pacific and East Asia is investigated using multiscale global tomography. Our results show the subducting Pacific and Philippine Sea slabs, as well as low-Vp zones in the crust and upper mantle beneath active arc volcanoes. The Pacific slab becomes flat in the mantle transition zone beneath East Asia, and a big mantle wedge (BMW) has formed above the flat slab. Active intraplate volcanism is caused by hot and wet upwelling flow in the BMW. Under the Izu-Bonin trench, the Pacific slab subducts all the way down to the core-mantle boundary. Beneath the Hainan hotspot, a whole-mantle plume is revealed. Under SE Asia, subducted slabs, mantle plumes and BMW are also imaged. Subslab hot mantle upwelling (SHMU) occurs below the Australian slab, probably due to return flow of the slab deep subduction. Slab holes are revealed under North Sumatra and eastern Java. Hot upwelling flow in the mantle wedge above the slab is connected with SHMU via the slab holes, suggesting that mixture of island arc magma and SHMU may have caused super-eruptions of the Tambora and Rinjani volcanoes in eastern Java and the Toba volcano in North Sumatra.