第121回ジオダイナミクスセミナー
　　　Geodynamics Seminar

要　旨
　In order to better understand the structure and seismotectonics of the entire arc of Tohoku Japan and Hokkaido in Japan, we combined arrival time data from earthquakes beneath the land area and sub-oceanic earthquakes in the Pacific Ocean to image three-dimension (3-D) P- and S-wave velocity structures under the entire arc from the Japan Trench and Kuril Trench to the coast area of the Japan Sea. We adopted 176,431 P- and 110,953 S-wave arrival times from 5123 local earthquakes and 2845 sP depth phase from 385 sub-oceanic events occurred beneath the Pacific Ocean. The 385 sub-oceanic events are accurately relocated by using the P-, S-wave and sP depth phase arrivals jointly. Our inversion results confirmed the major features delineated by the previous studies and revealed some new features of structural heterogeneity beneath the Northeast (NE) Japan forearc and Kuril forearc. The high velocity anomalies of the cold subducting Pacific slab and low velocity anomalies in the hot mantle wedge are imaged clearly. Strong lateral heterogeneities are revealed on the upper boundary of the Pacific slab under the forearc region, which shows a good correlation with the spatial distribution of large interplate earthquakes. These results indicate that strong coupling sections or asperities, weak coupled or decoupled patches perhaps exist along the upper boundary of Pacific slab. Widespread slow velocity anomalies are visible in the forearc mantle above the subducting Pacific slab, which may reflect the serpentinization of the forearc mantle associated with the dehydration process of the subducting slab. Our results also suggest a general tendency for seismic coupling in the asperities to be located surrounding the low velocity areas beneath the sub-oceanic region along the subducting plate in the Pacific Ocean.




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