HR: 08:00h
AN: S31B-01    [PDF]
TI: Can we achieve consistent inner-core models from ISC travel-time data and waveform data?
AU: Obayashi, M
EM: obayashi@jamstec.go.jp
AF: IFREE, Japan Marine Science and Technology Center, 2-15 Natsushima, Yokosuka, Kan 237-0061 Japan
AU: * Niu, F
EM: niu@rice.edu
AF: Department of Earth Science, Rice University, 6100 Main street, Houston, TX 77005 United States
AU: Wen, L
EM: Lianxing.Wen@sunysb.edu
AF: Dept. of Geosciences, SUNY at Stony Brook, Stony Brook, NY 11794 United States
AB: While it is now generally believed that the Earth's inner core is anisotropic to compressional wave propagation, the magnitude and existence of depth variations of seismic anisotropy are still controversial among the seismological community. Same is also true on whether there is a hemispherical variation in both the velocity (including the isotropic wavespeed and the magnitude of seismic anisotropy) and the attenuation structure at the top of the inner core. The discrepancy between the inner-core models is, however, deeply related to the type of data used in deriving them: hand-picked differential travel-time data ({\it PKiKP-PKIKP} and {\it PKP-PKIKP}), ISC absolute travel-time data of PKIKP, or normal-mode data. Models from the first type of data appear to have strong lateral and radial variations of seismic anisotropy, as well as the hemisphericity of the inner core, while the other two types of data tend to favor models with seismic anisotropy homogeneously distributed within the entire inner core. Such a discrepancy could result from the sparse and biased sampling of the differential travel-time data, or the large uncertainties in the ISC absolute travel-time data, or both. To solve this discrepancy, we analyzed a total of $\sim$2.1 million {\it PKIKP} travel time data reported to the International Seismological Center (ISC) in the period of 1964-1999. We first computed the ISC travel-time residuals of PKIKP with respect to the PREM model. We used high-quality relocation catalogs with relatively accurate earthquake locations and origin times in the calculation. We then calculated corrections on the {\it PKIKP} travel time due to the heterogeneous mantle structure. Our preliminary results suggested that the corrected travel-time residual data are, surprisingly, very consistent with differential travel-time data. For example, we found that travel times are systematically smaller, by about 0.5-2 s, for waves that travel the "eastern'' hemisphere compared to those travel the "western'' hemisphere. The consistence suggested that the ISC travel-time data, with its great coverage, has the potential to shed light on those unresolved regions, such as the innermost part of the inner core.
DE: 1015 Composition of the core
DE: 7203 Body wave propagation
DE: 7207 Core and mantle
DE: 8115 Core processes (1507)
SC: Seismology [S]
MN: 2003 Fall Meeting