HR: 0800h
AN: S31B-02    [Abstracts]
TI: Lower mantle phase-boundary variability
AU: * Sun, D
EM: sdy@gps.caltech.edu
AF: California Institute of Technology, Seismological Laboratory 252-21, Caltech, Pasadena, CA 91106, United States
AU: Helmberger, D
EM: helm@gps.caltech.edu
AF: California Institute of Technology, Seismological Laboratory 252-21, Caltech, Pasadena, CA 91106, United States
AB: A lower mantle S-wave triplication with a Scd branch occurring between S and ScS appears to be explained by a recently discovered Perovskite (PV) to Post-Perovskite (PPV) phase-change. It is predicted to have a positive Clapeyron slope (γ) between 5 to 13 MPa/K with a small S-velocity jump (1.5 to 4%) and an even smaller 1 to 2% jump in P-velocity. Seismic observations indicate that Scd arrives earlier and stronger beneath fast regions (circum-Pacific) than slow regions (super plumes) indicating a positive γ. However, it proves difficult to separate effects produced by downwelling (slab debris) from upwelling (plumes) in refining the actual physical properties. Here we model dense record sections collected from USArray and existing PASSCAL data to isolate effects produced by lower mantle structure as evidenced by P and S tomographic models, to better define the seismic phase-change properties beneath Central America. We find that the PV-PPV velocity jump is twice as strong beneath slow regions as fast regions requiring distinct reference heights indicative of changing chemistry. Moreover, the edges of the supposed buckled slabs deliminated by both P and S-waves display very rapid changes in phase-boundary heights producing Scd multipathing. These features can explain the unstable nature of this phase with easy detection to no detection commonly observed. The fine structure at the base of the mantle beneath these edges contains particularly strong reflections indicative of local ultralow velocity zones, which is predicted by some dynamic models.
DE: 7203 Body waves
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7290 Computational seismology
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
SC: Seismology [S]
MN: 2007 Joint Assembly