*Younghee Kim1, Xuzhang Shen2, Teh-Ru Alex Song3, Hobin Lim1 (1.Seoul National University, South Korea, 2.Lanzhou Institute of Seismology, China Earthquake Administration, China, 3.Seismo Lab, Department of Earth Sciences, University College London, UK)
S (Solid Earth Sciences) » S-IT Science of the Earth's Interior & Tectonophysics
[S-IT31] [EE] Revisit Bullen's layer C - Mantle transition zone and beyond
Mon. May 22, 2017 3:30 PM - 5:00 PM Poster Hall (International Exhibition Hall HALL7)
convener:Teh-Ru Alex Song(University College London), Younghee Kim(Seoul National University), Xuzhang Shen(Lanzhou Insititute of Seismology, China Earthquake Administration), Yoshio Fukao(Center for Earthquake and Tsunami / Japan Agency for Marine-Earth Science & Technology)
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.
*Xiaobo He1 (1.Dept. of Marine Sciences, Zhejiang University)