第86回ジオダイナミクスセミナー
　 　Geodynamics　Seminar

要　旨
　Tomographic models for the Earth's mantle based on conventional ray-theoretical interpretation of teleseismic travel-time shifts have revealed spatial variations in compressional and shear velocity anomalies on various scales. Ray theory is valid, however, strictly only for a hypothetical infinite-frequency wave, while observed seismic waves have a finite-frequency range undergoing diffractive wavefront healing and are sensitive to three-dimensional (3-D) structures off the geometrical raypaths. This fundamental limitation in ray theory leaves large uncertainties in the determinations of the magnitude and shape of the anomalous mantle structures. A more rigorous theory for a finite-frequency travel-time shift, hereinafter referred to as finite-frequency kernel theory or banana-doughnut theory, yields a hollow banana-doughnut-shaped sensitivity, which is identically zero right on the ray. In this talk, recent investigation into the theoretical underpinnings of finite-frequency kernel theory will be briefly reviewed. A new tomographic method that makes use of 3-D banana-shaped sensitivity of finite-frequency travel times is then employed to image high-resolution subsurface velocity structure beneath the Iceland hotspot. The results from kernel-obtained tomography will be compared with those from standard ray-based tomography.


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