HR: 17:45h
AN: DI24A-08    [Abstracts]
TI: Topography of inner core boundary
AU: * Song, X
EM: xsong@uiuc.edu
AF: Department of Geology, University of Illinois, Urbana, IL 61801, United States
AU: Dai, W
EM: wdai@uiuc.edu
AF: Department of Geology, University of Illinois, Urbana, IL 61801, United States
AB: Precise determination of the topography of a major internal boundary of the Earth is difficult because of the trade-off with the unknown velocity structure above it. However, the discoveries of the inner core (IC) rotation and high-quality teleseismic waveform doublets make the precise mapping of the topography of the inner core boundary (ICB) possible, as demonstrated in recent studies. Here we examine IC refracted (PKP-DF) and reflected (PKP-CD) waves recorded at the Yellowknife Array and global stations from 13 high-quality doublets, among a large collection of doublets in S. Sandwich Islands that we have assembled. Our results show clear evidence for spatial and temporal variations of IC reflections in travel times and in waveforms. If the time separation (dT) between the two members of the doublet is less than 3 years, the IC arrivals show little temporal change in travel times or waveforms. If dT is greater than about 6 years, some doublets show large variations but some others do not. The ICB regions beneath Atlantic Ocean and Indian Ocean show little temporal change. The regions show large variations are beneath Africa and the Central America, which coincide with large seismic anomalies at the core-mantle boundary (CMB). Inside these two ICB regions, there are fine-scale (km scale) variations. The largest temporal changes of IC reflections are about 0.10 to 0.15 s, corresponding to a topographic variation of up to 3.7 to 5.6 km. The results suggest ICB topography of a few kms on fine to regional scales. Dynamical models include a bumpy ICB rotating with the IC itself or a transient slurry boundary sloshing about in the turbulence at the base of the convecting outer core. The geographical coincidence of the ICB and CMB anomalies may suggest strong thermal coupling of the mantle and the core.
DE: 1507 Core processes (1213, 8115)
DE: 7203 Body waves
DE: 7207 Core (1212, 1213, 8124)
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
SC: Study of the Earth's Deep Interior [DI]
MN: 2007 Fall Meeting