第90回ジオダイナミクスセミナー
　　　Geodynamics　Seminar

　　　　　　　　　　
　　　　　　　　「トンガ下のマントル遷移層構造」
"Structure of the mantle transition zone beneath the Tonga region"

　　　　　　　　講師：今任嘉幸（愛媛大学修士１年）

　　 　　　　　 　　　　　
　　　　　主催　：　愛媛大学地球深部ダイナミクス研究センター
　　　　　日時　：　２００４年２月１３日（金）　午後17時〜
　　　　　場所　：　愛媛大学理学部講義棟　２０１教室

要　旨
　Mineral physics studies suggest that the phase change at the 410 km discontinuity has a positive Clapeyron slope, while the 660 km discontinuity has a negative slope. Thus near the cold subducting slab the 410 may be uplifted to a shallower depth, while the 660 is depressed to a greater depth. Hence the mantle temperature has a great influence on the depth variations of the two mantle discontinuities.In this study I have investigated the depth variations of the 410 and 660 km discontinuities and estimated the lateral variation in the thickness of the mantle transition zone beneath the Tonga region using S-to-P converted phases.A Phase Weighted Stacking method has been used in this study because these converted phases usually have small amplitudes which are not identifiable in each seismogram. Several S-to-P converted and reflected waves at the mantle discontinuities are clearly detected in the stacked waveforms.My results show that in the vicinity of Vanuatu trench the mantle transition zone becomes thicker due to the subducting Australian plate. In the centeral parts of Tonga region the 410 discontinuity becomes deeper due to the influence of hot materials as imaged by seismic tomography. In the vicinity of Tonga trench the mantle transition zone becomes thicker layer due to the subducting Pacific plate.




　　　　　　　　問い合わせ先：山崎　大輔 　TEL　　　（089）927-8408
　　　 　　　　　　　　　　　　　　　　E-mail　　yamazaki@sci.ehime-u.ac.jp