第82回ジオダイナミクスセミナー
　　　Geodynamics　Seminar

　　　　　　　　　　
"Crustal structure and Moho topography beneath southwest Japan
as estimated from crustal reflected waves"
　　　　　　　
　　　　　講師：Mohamed K. Salah（愛媛大博士3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　：　２００３年１２月５日（金）　午後17時〜
　　　　　場所　：　愛媛大学理学部講義棟　２０１教室

要　旨
　In this study we have tried to detect and collect later phases reflected at the surface and/or at the Moho discontinuity and use them to study the velocity structure as well as the Moho depth variation beneath southwest (SW) Japan. Taking the advantage of the high-quality and high-quantity of Hi-net waveform data now available, we have detected a large number of direct and Moho-reflected phases. We have used these phases to obtain the Vp and Vs crustal structures and to estimate the depth distribution of the Moho discontinuity in the study area using the travel time differences between these later phases and the first P and S arrivals. Our results revealed significant low velocity anomalies beneath the active and Quaternary volcanoes in SW Japan. Results obtained using each data set (P, PmP, S, SmS and sSmS) separately are generally consistent with each other and all showed low velocity anomalies beneath most of the active and Quaternary volcanoes and along the eastern part of Shikoku and Kii Peninsula. Ray-path analysis of direct phases showed that the data set used have quite good ray coverage that is sufficient to accurately locate the velocity anomalies in the study area. In addition, results of the checkerboard resolution test indicate that these structures are generally well recovered and that adding later phases could significantly improve the resolution of the tomographic images compared to those from first arrivals alone. Results of the Moho depth estimation were in general agreement with most of the previous results. The Moho is generally deep beneath the land area at about 31-33 km and gets shallower to about 28-30 km beneath the coastlines of the Japan Sea and the Pacific Ocean.



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