HR: 0800h
AN: U41B-0404    [Abstracts]
TI: Constraints on shear-velocity reductions in the lowermost mantle by using ScP postcursor data
AU: * Idehara, K
EM: idehara@sci.ehime-u.ac.jp
AF: Geodynamics Research Center, Ehime University, Matsuyama 790-8577, Japan, Matsuyama, 790-8577, Japan
AU: Yamada, A
EM: yamada@sci.ehime-u.ac.jp
AF: Geodynamics Research Center, Ehime University, Matsuyama 790-8577, Japan, Matsuyama, 790-8577, Japan
AU: Zhao, D
EM: zhao@aob.geophys.tohoku.ac.jp
AF: Department of Geophysics, Tohoku University, Sendai 980-8578, Japan, Sendai, 980- 8578, Japan
AB: Lateral distributions of the ultralow-velocity zones (ULVZs) at the base of the mantle are constrained by ScP waves reflected and converted at the core-mantle boundary (CMB). The amplitude of postcursor to ScP, which is excited at the ULVZ surface, is strongly dependent on the shear velocity contrast and has been proven to be a very powerful probe for detecting the localized ULVZs in previous studies. In this study, we have assembled a large amount of waveform data of ScP recorded at short-period seismic stations deployed in the Japan Islands and world-wide seismic stations of International Monitoring System. Clear arrivals of postcursor are detected beneath Philippine-Kalimantan and East of Australia, indicating shear velocity reductions of 15% to 40%. On the other hand, no postcursor is found beneath North Pacific and the Asian continent. The estimation of noise levels of waveforms bounced in North Pacific and the Asian continent indicates that there is no significant boundary with shear wave velocity reduction over 5% in the lowermost mantle under those regions.
DE: 1025 Composition of the mantle
DE: 1212 Earth's interior: composition and state (7207, 7208, 8105, 8124)
DE: 7207 Core (1212, 1213, 8124)
DE: 7208 Mantle (1212, 1213, 8124)
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
SC: Union [U]
MN: 2007 Fall Meeting