Focal mechanisms of deep-focus earthquakes show compressional stress fields in the deepest part of upper mantle slabs. We examine mechanisms to realize the stress fields using numerical models of slabs interacting with a phase and/or a chemical boundary. The compressional stress field implies that compositional density difference greater than 2% exists at the 660km discontinuity, or that viscosity increases by a factor larger than a few tens and linear-law rheology dominates the flow mechanism in the lower mantle.
As our basic work to establish precisely the reference isotopic abundance ratios of ruthenium, we examined carefully the isotopic abundance ratios of seven stable isotopes of ruthenium using its solution prepared by Aldrich Chemical Co., Inc., Milwaukee, WI, USA. Prior to our examination, Poths, Schmitt-Strecker and Begemann (1987) at Max-Planck-Institut für Chemie, Mainz, also determined precisely the corresponding ratios using Ru of Ventron-Alpha Co. Our 98Ru/99Ru ratio is about 11 ε higher than that reported by Poths et al., while our 104Ru/99Ru ratio is about 10 ε lower than that by them. As regards 96Ru, 100Ru, 101Ru and potentially 99Ru, there are little if any remarkable differences between us and them. The difference in 104Ru/99Ru is judged to reflect the interference from (88Sr16O)+ ion in their measurement. However, it is difficult to account for the difference in 98Ru/99Ru ratio. One cannot rule out the possibility that this has resulted from the difference in nuclear-decay contribution from 98Tc.