HR: 0800h
AN: U21A-0006    [Abstracts]
TI: Illuminating Slab Remnants in the Lower Mantle Using PKP Precursors
AU: * Romanowicz, B A
EM: barbara@seismo.berkeley.edu
AF: Berkeley Seismological Laboratory, 215 McCone Hall, Berkeley, CA 94720, United States
AU: Cao, A
EM: acao@seismo.berkeley.edu
AF: Berkeley Seismological Laboratory, 215 McCone Hall, Berkeley, CA 94720, United States
AB: High quality recordings at the Yellowknife seismic array (YK) provide a good opportunity to locate the scatterers responsible for some of the observed PKP precursors, specifically those that appear well separated on the seismograms. Using data from high quality earthquake doublets, we have shown (Cao and Romanowicz, EPSL, 2007) that it is possible to precisely locate the scatterers responsible for these precursors, and determine whether they originate from the PKPbc or the PKPab phase, and on the source or receiver side. We have now expanded this dataset to non-doublet events. The most reliably measured individual scatterers delineate a region in the lowermost mantle where tomographic models indicate the presence of a transition from fast to slow velocities, likely associated with subducting slabs. To produce the scatterers, this transition should be sharper than seen in large scale tomographic models. This provides evidence for the penetration of slabs deep into the lower mantle beneath western North America and for the persistence of heterogeneity in composition during the slab's slow descent to the core-mantle boundary.
DE: 7200 SEISMOLOGY
DE: 7203 Body waves
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 7299 General or miscellaneous
SC: Union [U]
MN: 2007 Fall Meeting