2017年5月22日(月) 10:45 〜 12:15 202 (国際会議場 2F)

コンビーナ:Teh-Ru Alex Song(University College London)、Younghee Kim(Seoul National University)、Xuzhang Shen(Lanzhou Insititute of Seismology, China Earthquake Administration)、深尾 良夫(地震津波海域観測研究開発センター/海洋研究開発機構)、座長:Song Teh-Ru Alex(University College London)、座長:Kim YoungHee(海洋研究開発機構)

Large seismic velocity gradient between 400 km and 1000 km depth led Bullen in 1940 to the construction of the layer C, which includes the mantle transition zone and uppermost lower mantle defined in the preliminary reference earth model, or PREM. While phase transition of olivine to its high pressure polymorphs generally defines the 410 and 660 km seismic discontinuities, several interesting findings associated with the lower half of the layer C are somewhat difficult to be reconciled with the olivine phase transition alone. First, just below the 660 seismic discontinuities, travel time and triplication data typically define a large velocity gradient down to about 800 km depth. Second, observations of high frequency seismic scattering originating from 700 to 1000 km depths remain puzzling. Third, in some latest global tomographic models, positive radial anisotropy appears prominent near or below the slab in the upper lower mantle. Fourth, downgoing slabs and upwellings interpreted in recent tomographic models are not always linked to the olivine phase boundaries and they frequently experience strong distortion near the bottom of the layer C.



If the internal structure of the Earth and its layering are evolved from long term mantle convection and mechanical mixing due to plate construction or destruction over billions of years, one may attempt to understand the nature of seismic complexities in the layer C as a whole. One may ask how the layer C controls modern mass and heat advection in the mantle. If the layer C is compositionally inhomogeneous with depth, one may wish to refine its density profile and discuss plausible dynamic consequences.



This session solicits all efforts characterizing seismic properties in all wavelengths in the layer C, and we also encourage integrated and multidisciplinary efforts to help untangle the nature and the dynamic impact of the layer C.