HR: 09:30h
AN: MR21A-07    [Abstracts]
TI: Is there a Post-Perovskite layer beneath the African Superplume?
AU: Helmberger, D
EM: helm@gps.caltech.edu
AF: Seismological Laboratory, Caltech 252-21, pasadena, ca 91125 United States
AU: * Ni, S
EM: stone@gps.caltech.edu
AF: Seismological Laboratory, Caltech 252-21, pasadena, ca 91125 United States
AU: Sun, D
EM: sdy@gps.caltech.edu
AF: Seismological Laboratory, Caltech 252-21, pasadena, ca 91125 United States
AB: Most tomographic models display relatively fast velocity patches beneath regions involving past subduction. Synthetic seismograms generated for such models will produce a small triplication matching S, Scd and ScS data sets, if we allow a small jump in velocity of 1% or more, depending on the global model (Sidorin et al, 1999; Ni et al., 1999). The variation in observations from patch to patch suggests a positive Clapeyron Slope ($\gamma$) of about 6 megapasscal per Kelvin which produces the layer thickness varying from 300km (fast regions) to 60 km (slow regions). Assuming a larger $\gamma$ can eliminate the layer in the slower regions. \par Here we attempt to detect such a boundary beneath the African Superplume by examining data along a 2D section from South Sandwich Island to Arabia, including several arrays. Close examination of paths where ScS is nearly in the middle of the structure reveal simple looking waveforms where (ScS-S) waveform observations are similar to PREM synthetics. Perhaps, the jump associated with a possible phase change in velocity occurs near the onset of the thin CMB thermal-boundary-layer with a negative change producing near cancellation, or it is not present. Since this large structure seems unique in terms of relative sharp walls (lateral boundaries), it may have unique chemistry as well.
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 3919 Equations of state
DE: 3924 High-pressure behavior
SC: Mineral and Rock Physics [MR]
MN: 2004 AGU Fall Meeting