HR: 16:15h
AN: U34A-02 INVITED     [Abstracts]
TI: Evidence for a plum pudding mantle from deep seismic scattering
AU: * Shearer, P
EM: pshearer@ucsd.edu
AF: IGPP/SIO, U.C. San Diego, La Jolla, CA 92093-0225 United States
AU: Earle, P
EM: pearle@usgs.gov
AF: U.S. Geological Survey, MS 966 DFC PO Box 25046, Denver, CO 80225 United States
AU: Hedlin, M
EM: hedlin@ucsd.edu
AF: IGPP/SIO, U.C. San Diego, La Jolla, CA 92093-0225 United States
AB: Recent analyses of PKP precursors and other seismic phases indicate scattering from small-scale heterogeneities in the deep mantle. These features are almost certainly compositional in origin because thermal perturbations would not last very long at the 5 to 20 km scale length of the anomalies. These results support ``plum pudding'' models of the mantle, in which incomplete mixing permits small blobs of chemically distinct material to persist for many convection cycles. In general, analyses of short-period scattered waves provide a window into deep Earth structure at much finer scales than those resolved by tomographic inversions for three-dimensional seismic velocities. Recent computational advances permit modeling of scattering throughout the Earth, despite large differences in scattering strength. Most observations to date can be roughly explained with about 4% RMS velocity heterogeneity in the upper 200 km of the mantle and 0.5% heterogeneity in the lower mantle, although there are also large geographic variations in scattering strength.
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 7203 Body wave propagation
DE: 7207 Core and mantle
SC: Union [U]
MN: 2004 AGU Fall Meeting