HR: 11:25h
AN: U32A-04    [Abstracts]
TI: Origin of SdS and PdP and Implications for a D" Phase Change
AU: * Cormier, V F
EM: vernon.cormier@uconn.edu
AF: University of Connecticut, Physics Department, Storrs, CT 06269-3046 United States
AU: Fitzpatrick, M
EM: mfitz@tvcconect.net
AF: University of Connecticut, Physics Department, Storrs, CT 06269-3046 United States
AB: Precursors to ScS and PcP seismic phases, often labeled as SdS or PdP, have been included in evidence for a sharp discontinuity in seismic velocities at depths between 100 and 300 km above the core-mantle boundary (the D^"region). The poor lateral coherence of observed SdS and PdP may be consistent with either the effects of constructive interference of distributed heterogeneity in D^"or topography on a discontinuity or both. P and S wavefields interacting with 2-D models of D^" heterogeneity are modeled by a pseudospectral method. Structures examined include a discontinuity with topography, spatially continuous heterogeneity, and bimodal models of heterogeneity containing either high velocity inclusions (solid-solid phase changes) or low velocity inclusions (partial melt regions). Deterministic models of topography on a D^" discontinuity are generated from tomograms, an assumed temperature derivative of velocity, and a Clapeyron slope of a perovskite phase change. Synthetics from these models are compared with 2-D waveform profiles to determine whether existing tomograms of the D^" region can predict the observation of PdP and SdS phases, their amplitudes relative to PcP and ScP, and their lateral coherence.
DE: 7203 Body wave propagation
DE: 7207 Core and mantle
DE: 7260 Theory and modeling
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 9810 New fields (not classifiable under other headings)
SC: Seismology [S]
MN: 2005 Joint Assembly