HR: 16:30h
AN: U44A-03 INVITED    [Abstracts]
TI: Global Predictions of the Post-Perovskite Phase Thickness
AU: * Sun, D
EM: sdy@gps.caltech.edu
AF: Seismological Laboratory, California Institute of Technology, 252-21, Caltech, Pasadena, CA 91125,
AU: Helmberger, D
EM: helm@gps.caltech.edu
AF: Seismological Laboratory, California Institute of Technology, 252-21, Caltech, Pasadena, CA 91125,
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. Recent mineral physics experiments indicate a positive Clapeyron slope (γ) between 5 to 13 MPa/K with a small S-velocity jump and an even smaller P-velocity jump cross the phase boundary. Earlier, Sidorin et al. (1999) used a mapping of δVs from Grand's tomographic model to estimate ΔT (temperature) and the differential times (Scd-S) to determine a global reference height (h_ph = 200 km) and a γ = 6 MPa/K assuming a jump in shear velocity β = 1.5%. Here we use the δVs to estimate h_ph and β locally by matching synthetics to observations over the S-Scd-ScS window to set up a mapping parameterization. The timing separation between (Scd-S) fixes the phase onset (PV to PPV) and (ScS-Scd) fixes the phase return (PPV to PV). We find that the 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 delineated by both P and S-waves in tomographic display very rapid changes in phase boundary heights producing complex Scd waveforms. These features can explain the scatter in (Scd-S) data sets and the unstable nature of this phase with easy detection to no detection commonly observed. We generate global models for various values of γ's, displaying the temperature at the phase boundary and PPV thickness. The temperature variation for γ = 3 Mpa/K is over 1000 K which appears extreme based on effects produced by sinking slab rates. Values of 6 <γ< 12 MPa/K appears to be easiest to reconcile with seismic data, although the PPV thickness is poorly sampled beneath the Superplumes.
DE: 1212 Earth's interior: composition and state (7207, 7208, 8105, 8124)
DE: 7203 Body waves
DE: 7208 Mantle (1212, 1213, 8124)
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
SC: Union [U]
MN: 2007 Fall Meeting