HR: 1340h
AN: T43A-1317    [Abstracts]
TI: Constraining Inner Core Rotation From a Worldwide Search of Waveform Doublets
AU: Li, Y
EM: yli13@uiuc.edu
AF: Dept. of Geology, Univ. of Illinois at Urban-Champaign, 1301 W. Green St. 245 NHB, Urbana, IL 61801 United States
AU: * Song, X
EM: xsong@uiuc.edu
AF: Dept. of Geology, Univ. of Illinois at Urban-Champaign, 1301 W. Green St. 245 NHB, Urbana, IL 61801 United States
AU: Sun, X
EM: xsun@uiuc.edu
AF: Dept. of Geology, Univ. of Illinois at Urban-Champaign, 1301 W. Green St. 245 NHB, Urbana, IL 61801 United States
AB: A major debate in determining inner core rotation using seismic PKP differential times has been potential systematic event mislocation. The problem can be avoided by using waveform doublets separated by several years (Li and Richards, 2003). The high similarity of the whole waveforms in a doublet ensures that the two events indeed occur at the same location and sample the same Earth structure. The waveform similarity also allows measurements of relative time shifts with high precision. Motivated by the recent successful discovery of waveform doublets of South Sandwich Islands (SSI) earthquakes that show clear temporal changes at stations in Alaska and Canada (Zhang et al., this session), we are conducting a worldwide search for waveform doublets. We have designed an efficient search scheme, which involves initial pairing of earthquakes at a targeted region using catalog locations and semiautomatic correlation and visualization using MATLAB. Our search on SSI earthquakes have yielded 12 new doublets that are separated by 0, 1, 3, 4, 6, 7, 8, 13, 15, 18, 18, 23, and 33 years. When aligned with the PKP(BC) phase (turning at the bottom of the outer core), the PKP(DF) phase (traversing the inner core) of the later event is consistently earlier for the pairs with the time separation greater than 7 years, but pairs separated by less than 4 years show little travel time shifts. The Jul 25, 1970 event forms a triplet with the 1993 and 2003 doublets discovered by Zhang et al. (this session). The DF phase is earlier by 0.35 to 0.40 s over 33 years. We will report our search results on Alaska and Kermadec earthquakes for which evidence for temporal changes in BC-DF times has been reported (along Alaska to South Pole and Kermadec to Norway paths). Waveform doublets will also allow us to examine possible changes in travel times or amplitudes of other phases that sample the inner core (such as PKiKP, PKKP, and inner core scattering waves).
DE: 8115 Core processes (1507)
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 7203 Body wave propagation
DE: 7207 Core and mantle
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting