第95回ジオダイナミクスセミナー
　 　Geodynamics　Seminar

要　旨
　We present seismic images of the upper mantle beneath the active intraplate Changbai volcano in Northeast Asia determined by teleseismic travel time tomography.Our results show a columnar low-velocity anomaly extending to 400 km depth under Changbai. High velocity anomalies are visible in the mantle transition zone, and deep earthquakes occur at depths of 500-600 km under the region, suggesting that the subducting Pacific slab is stagnant in the transition zone. These results suggest that the Changbai intraplate volcano is not a hotspot like Hawaii but a kind of back-arc volcano related to the deep subduction and stagnancy of the Pacific slab under Northeast Asia. A 3-D ray tracing technique is used to investigate ray path variations of P, PcP, pP and PP phases in a global tomographic model. Our results suggest that if the blocks or grid nodes adopted for inversion are relatively large (3-5 degrees) and onlya low-resolution 3-D model is estimated, 1-D ray tracing may be feasible; but if fine blocks or grid nodes are used to determine a high-resolution model, 3-D ray tracingbecomes necessary and important for the global tomography.







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　　　 　　　　　　　　　　　　　　　　E-mail　　yamazaki@sci.ehime-u.ac.jp