HR: 0800h
AN: U41B-0409    [Abstracts]
TI: Is the double crossing phase transition in D" ubiquitous?
AU: * Kawai, K
EM: kenji@geo.titech.ac.jp
AF: Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo, 152-8551, Japan
AU: Geller, R J
EM: bob@eps.s.u-tokyo.ac.jp
AF: University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo, 113-0033, Japan
AU: Fuji, N
EM: fuji@eps.s.u-tokyo.ac.jp
AF: University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo, 113-0033, Japan
AB: By using waveform inversion to study the seismic velocity structure of D^'', we found that the upper half of D^'' beneath Central America has S-wave velocity significantly in excess of PREM, while the lower half has S-velocity nearly equal to PREM [Kawai et al., GRL, 2007]. We interpret this as evidence for a double crossing phase transition (a reverse transition from post-perovskite=ppv to perovskite=pv), the existence of which was suggested by Hernlund et al. [2005, Nature]. In addition to the D^'' layer beneath Central America, we have now also inverted seismic body- wave waveform data for the vertical dependence of (isotropic) shear-velocity in D^'' beneath Asia and the Arctic, also using the transverse components of relatively long period broadband waveforms (20-200 s) as data. We found that these data also suggest the existence of high S-velocity in the upper half of D^'' and low velocity in the lower half, consistent with the existence of a double crossing phase transition within D^''. Our results for these three separate regions, when taken together, suggest that the existence of a double crossing phase transition is widespread and possibly global or nearly so. This has important implications for studies of the mineral physics, temperature profile, convection and material transport in D^''. In the near future, we plan to study D^'' beneath Africa and the Pacific in order to further determine the extent to which the double crossing phase transition is (or is not) ubiquitous.
DE: 1212 Earth's interior: composition and state (7207, 7208, 8105, 8124)
DE: 7203 Body waves
DE: 7208 Mantle (1212, 1213, 8124)
SC: Union [U]
MN: 2007 Fall Meeting