HR: 09:30h
AN: S51A-06    [PDF]
TI: Searching for sharp lower-mantle discontinuities in the lower mantle beneath the western United States by stacking thousands of P-to-S converted phases
AU: Liu, K H
EM: liu@ksu.edu
AF: Kansas State University, 108 Thompson Hall, Department of Geology, Manhattan, KS 66506
AU: * Gao, S S
EM: gao@ksu.edu
AF: Kansas State University, 108 Thompson Hall, Department of Geology, Manhattan, KS 66506
AB: The existence (or confirmed non-existence) of velocity discontinuities in the lower mantle is critical for a number of first-order problems in geoscience, such as the style of mantle convection, and phase change and chemical composition in the lower mantle. So far positive identification of sharp lower-mantle discontinuities on a large scale is scarce. We hand-selected about 3000 high-quality receiver functions from shallow (80 km or less) earthquakes recorded by broadband seismic stations in California, made moveout corrections along the time of P-to-S converted phases, and performed an n-th root stacking to form a single depth image. About a dozen apparent arrivals have been imaged for the depth range of 700 to 2000 km. To identify and reject false discontinuities associated with non P-to-S phases, we generated a synthetic seismogram using CORE (Complete Ordered Ray Expansion, Clarke and Silver, 1993) for each of the 3000 seismograms by taking account the actual focal parameters. We then processed the synthetic seismograms using exactly the same procedure as what was used for the real data, and generated a synthetic depth image. Comparison between the observed and synthetic depth images suggest that about six of the 12 observed arrivals do not correspond to arrivals on the synthetic image, and are thus likely to represent real lower-mantle discontinuities. Those positively identified discontinuities are in the depths of about 1040, 1080, 1230, 1400, 1600, and possibly 2000 km. Comparison with previous observations and implications of those discontinuities will be presented.
DE: 7200 SEISMOLOGY
DE: 7203 Body wave propagation
DE: 7207 Core and mantle
DE: 7299 General or miscellaneous
SC: Seismology [S]
MN: 2003 Fall Meeting