Evidence of seismic anisotropy and a lower temperature condition in the D″ layer beneath Pacific Antarctic Ridge in the Antarctic Ocean

Deep Earth Structure: Lower Mantle and D″

“…The large majority of observations involve horizontally polarized shear-wave components (SH) traveling faster through D 00 than vertically polarized shear waves (SV) for grazing incidence or wide-angle reflections, with relatively large-scale regions of D 00 displaying 0.5-1.5% anisotropy (e.g., Fouch et al, 2001;Garnero and Lay, 2003;Kendall and Silver, 1996;Ritsema, 2000;Rokosky et al, 2004;Thomas et al, 2007Thomas et al, , 2011Usui et al, 2005Usui et al, , 2008Vinnik et al, 1998b;Walker et al, 2011;Wang and Wen, 2007b;Wookey and Kendall, 2008). While almost none of the studies have significant azimuthal raypath sampling, the observations are at least compatible with extensive vertical transverse isotropy, as may be caused by hexagonally symmetrical material with a vertical symmetry axis or fine-scale horizontal layering.…”

Elastic, vibrational, and thermodynamic properties of MgGeO3 postperovskite investigated by first principles simulation

“…These are very different from the case of MgSiO 3 , where the S wave of PPv shows a distinct positive jump of +1.5% [ Tsuchiya et al , 2004b], being consistent with the typical character of the D″ discontinuity [ e.g. , Usui et al , 2005, 2008]. In this point, the elasticity of MgGeO 3 PPv is not completely analogous to that of MgSiO 3 , since the transition pressures are of course determined by the thermodynamic energy balance, which is not directly connected to the elasticity.…”

“…Polarization anisotropy of S waves in the transversely isotropic media, which is more directly connected to the seismic anisotropy in D″ [ Garnero and Lay , 1997; Usui et al , 2005, 2008], is defined as A S T = ( V SH − V SV )/ V S × 100, where V SH ( V SV ) is horizontally (vertically) polarized S wave propagating horizontally [ Tsuchiya et al , 2004b]. V S are the usual isotropic averages.…”

“…[14] Polarization anisotropy of S waves in the transversely isotropic media, which is more directly connected to the seismic anisotropy in D 00 [Garnero and Lay, 1997;Usui et al, 2005Usui et al, , 2008, is defined as…”

Mineralogy under extreme conditions

“…Discovery of this Fe-rich ppv phase may open a new paradigm for Earth's D 00 layer and core-mantle boundary, where the crystalline silicate mantle meets the molten iron core and the Fe-rich ppv may be the major phase. This phase may play a central role in Fe exchange and chemical interaction between core and mantle, and dictate seismic velocities and heat transfer in the boundary layer (Hirose et al, 1999;Mao et al, 2004Mao et al, , 2006aTsuchiya et al, 2005;Wentzcovitch et al, 2006;Yamazaki et al, 2006;Maruyama et al, 2007;Idehara et al, 2007;Usui et al, 2008).…”