Solid Earth Sciences(S)
Session Sub CategoryScience of the Earth's Interior & Tectonophysics
Session IDS-IT31
TitleRevisit Bullen's layer C - Mantle transition zone and beyond
Short titleMantle transition zone and beyond
Main ConvenerNameTeh-Ru Alex Song
AffiliationUniversity College London
Co-Convener 1NameYounghee Kim
AffiliationSeoul National University
Co-Convener 2NameXuzhang Shen
AffiliationLanzhou Insititute of Seismology, China Earthquake Administration
Co-Convener 3NameYoshio Fukao
AffiliationCenter for Earthquake and Tsunami / Japan Agency for Marine-Earth Science & Technology
ScopeLarge 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.
Type of presentationOral and Poster presentation
Invited authorsMaxim Ballmer (Institute of Geophysics, ETH Zurich)
Nicholas Mancinelli (Department of Earth, Environmental, and Planetary Sciences, Brown University)