HR: 0800h
AN: S41C-1026    [Abstracts]
TI: Complex Seismic Anisotropy in the Earth's Inner Core Beneath Africa
AU: * Yu, W
EM: yu@mantle.geo.sunysb.edu
AF: Department of Geosciences, Stony Brook University, Stony Brook, NY 11794-2100 United States
AU: Wen, L
EM: Lianxing.Wen@sunysb.edu
AF: Department of Geosciences, Stony Brook University, Stony Brook, NY 11794-2100 United States
AB: Seismic anisotropic velocity structure plays an important role in understanding the geodynamics and mineral physics in the Earth's inner core. Previous seismic studies using the PKiKP-PKIKP phase pairs have suggested no evidence for the presence of anisotropy in velocity in the top 80 km of the inner core. However, the sampling coverage of the PKiKP-PKIKP phase pairs in previous studies was limited, especially along the polar paths. Here we expand our PKiKP-PKIKP dataset by collecting the PKiKP-PKIKP waveforms sampling the inner core globally and along various sampling directions. Our data are selected from the Global Seismographic Network and many regional seismic networks: GEOSCOPE, GEOFON, the Canadian National Seismic Network (CNCN), the Oceanographic Hemisphere Project (OHP), Kazakhstan, and Kyrgyzstan. Our seismic observations show that there is indeed no difference in PKiKP-PKIKP differential travel time residual between the polar and equatorial paths in most regions of the inner core, suggesting no anisotropy in velocity in the top 80 km of the inner core in most regions. Our expanded collection of the PKiKP-PKIKP phases, however, reveals a clear polar-equatorial difference in differential travel time residual in a localized region in the western hemisphere beneath Africa. The PKiKP-PKIKP data sampling along the polar paths in this area of the inner core also exhibit strong lateral variations, requiring the thickness of isotropic layer varying from 10 km or less beneath Uganda and western Africa to 50 km beneath Cameron and Congo. We will show the seismic data grouped according to their sampling regions in the inner core and anisotropic velocity models in each of these regions by waveform modeling the PKiKP-PKIKP data, the PKP data observed at the caustics distance range (141°-145°), and the PKPbc-PKIKP data recorded at larger distances.
DE: 7200 SEISMOLOGY
DE: 7203 Body waves
DE: 7207 Core (1212, 1213, 8124)
DE: 8115 Core processes (1213, 1507)
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
SC: Seismology [S]
MN: Fall Meeting 2005