HR: 0800h
AN: S41C-1024    [Abstracts]
TI: Physical constraints on the ultra-low velocity zone at the lowermost mantle
AU: * Idehara, K
EM: idehara@sci.ehime-u.ac.jp
AF: Geodynamics Research Center, Ehime University, Bunkyo-cho 2-5, Matsuyama, 790-8577 Japan
AU: Yamada, A
EM: yamada@sci.ehime-u.ac.jp
AF: Geodynamics Research Center, Ehime University, Bunkyo-cho 2-5, Matsuyama, 790-8577 Japan
AU: Zhao, D
EM: zhao@sci.ehime-u.ac.jp
AF: Geodynamics Research Center, Ehime University, Bunkyo-cho 2-5, Matsuyama, 790-8577 Japan
AB: Array analysis of core-reflected phases recorded by the short-period array stations enables us to constrain the existence and properties of the ultra-low velocity zones (ULVZs) at the base of the mantle. In this work we have investigated the fine-scale ULVZ structure beneath the western Pacific region using PcP and ScP waves recorded by seismic array stations of the Hi-net network in Japan and the International Monitoring System. Densely sampled PcP and ScP data with high signal-to-noise ratios provide us robust evidence for spotty ultra-low velocity bodies near the core-mantle boundary beneath Philippine-Kalimantan and East of Australia. The observed ScP precursors and postcursors and the absence of PcP precursors can be best explained by a flat-layer ULVZ with the ratio of S-to-P velocity reductions of 2-2.5:1, and Vs-to-density ratio of -3:1, with S velocity reduction of up to 40%. The estimated ratio of Vs to Vp reduction is not very different from that of the experimental value by assuming purely thermal effect (1.8-2.2), although the large density jump (up to 13%) may suggest an enrichment of iron in the layer.
DE: 1212 Earth's interior: composition and state (7207, 7208, 8105, 8124)
DE: 1213 Earth's interior: dynamics (1507, 7207, 7208, 8115, 8120)
DE: 7208 Mantle (1212, 1213, 8124)
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
SC: Seismology [S]
MN: Fall Meeting 2005