HR: 0800h
AN: S31B-03    [Abstracts]
TI: Empirical transfer functions: Application to the determination of outermost core velocity structure using teleseismic SmKS phases
AU: * Eaton, D W
EM: deaton@uwo.ca
AF: University of Western Ontario, Department of Earth Sciences 1151 Richmond Street, London, ON N6A 5B7, Canada
AU: Alexandrakis, C
EM: calexan3@uwo.ca
AF: University of Western Ontario, Department of Earth Sciences 1151 Richmond Street, London, ON N6A 5B7, Canada
AB: Teleseismic SmKS waves propagate as S-waves in the mantle and compressional (K) waves in the core, with m-1 underside bounce points at the core-mantle boundary. For long-period or broadband recordings at epicentral distances of 115-135°, higher-order SmKS waves (3 ≤ m < ∞) are not often discernible as distinct pulses. Instead, they are typically manifested as a weakly dispersive waveform that lags SKKS by ~ 12-32s. In a ray-theoretical representation of this process, there is a strong geometrical similarity between the coalescence of SmKS turning waves to form a composite arrival and the interference of mantle S waves to form teleseismic Love waves. SmKS waves can thus be viewed as a type of pseudo-interface wave, the dispersive properties of which depend strongly on the fine-scale velocity structure of the outermost core. In order to analyze SmKS arrivals, we have developed an empirical transfer-function (ETF) technique that uses SKKS as a reference phase. An ETF is a wave-shaping filter that transforms the observed SKKS pulse into the observed SmKS pulse. We obtain this filter by windowing the respective pulses and applying frequency- domain Wiener deconvolution. Each ETF contains SmKS-SKKS differential arrival-time, phase-shift and relative-amplitude information; it also implicitly removes the source-time function and instrument response, thus facilitating the merging of results from different stations and events. Here, we apply this approach to global observations of SmKS phases and invert the results to yield a new velocity model for the outermost core region.
DE: 7200 SEISMOLOGY
DE: 7203 Body waves
DE: 7207 Core (1212, 1213, 8124)
DE: 7260 Theory
SC: Seismology [S]
MN: 2007 Joint Assembly