HR: 1340h
AN: T43A-1308    [Abstracts]
TI: Sensitivity Kernels of PKP Waves in the Lower Mantle and Inner Core
AU: * Calvet, M
EM: calvet@pontos.cst.cnes.fr
AF: Laboratoire de Dynamique Terrestre et Planetaire, UMR 5662, CNRS, Observatoire Midi-Pyrenees, 14 avenue Edouard Belin, Toulouse, 31400 France, Metropolitan
AU: Chevrot, S
EM: sebastien.chevrot@cnes.fr
AF: Laboratoire de Dynamique Terrestre et Planetaire, UMR 5662, CNRS, Observatoire Midi-Pyrenees, 14 avenue Edouard Belin, Toulouse, 31400 France, Metropolitan
AB: Traveltimes of PKP phases are often used to constrain the anisotropy of the inner core and the D'' layer structure. PKP waves on broadband records have rather short dominant periods (between 1 and 4 s), but because we need to consider the sensitivity of these waves far away from the source or the receiver, their first Fresnel zone is quite large. In order to provide a better interpretation of PKP(DF) residuals in terms of variations of anisotropy with depth in the inner core, we investigate the effects of transversely isotropic perturbations of the elastic tensor on the propagation of PKP(DF) waves. We show that three sensitivity kernels for traveltime and amplitude corresponding to three anisotropic perturbation parameters $\epsilon$, $\delta$ and $\gamma$ are required. To reduce the contributions of mantle heterogeneities, we can use PKP(AB)-PKP(DF) or PKP(BC)-PKP(DF) differential traveltimes to study the inner core anisotropy. However, heterogeneities in the lower mantle and D'' may still contribute strongly to the observed anomalies. Thus, obtaining good model of the D'' structure is a first step necessary to obtain reliable constraints on the inner core anisotropy. For this purpose, we derive and analyse the single phase and differential traveltime kernels for PKP in the mantle. The geometry of the differential kernels is complex because coupling occurs between the different PKP branches. As a result, the geometry of PKP differential kernels in D'' shows significant qualitative differences with simple ray tracing. A number of recent PKP studies have found strong variations of PKP(AB) traveltimes for very close paths. These observations suggest sharp lateral variations of seismic velocities in D'' whose origin and geometry are still poorly understood. Characterizing these anomalies will be possible using accurate 3-D sensitivity kernels.
DE: 7207 Core and mantle
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting