HR: 1340h
AN: T43A-1315    [Abstracts]
TI: Quantifying Inner Core Scattering from PKiKP Coda Waves
AU: * Leyton, F
EM: leytonfo@eas.slu.edu
AF: Saint Louis University, Dept. Eart & Atm. Sciences 3507 Laclede Ave., Saint Louis, MO 63103 United States
AU: Koper, K D
EM: koper@eas.slu.edu
AF: Saint Louis University, Dept. Eart & Atm. Sciences 3507 Laclede Ave., Saint Louis, MO 63103 United States
AB: It is thought that the core is mainly composed of iron, with a few percent of lighter elements. Despite its rather uniform composition, several authors have reported scattered energy coming from the inner core. This implies that the inner core has lateral variations in structure or composition with a scale length of tens of kilometers. These lateral variations represent seismic scatterers and could be caused by crystal grain size, variations in the orientation of anisotropy, or the presence of partial melt and/or impurities. However, it is still debated whether the scatterers are distributed throughout the volume of the inner core, or simply along the inner core boundary. This work pursues the characterization of inner core scattering (ICS) using a data set of high frequency PKiKP waveforms, recorded at short-period, small-aperture seismic arrays. We apply a methodology used in the study of heterogeneities in the crust and upper mantle, which consists of curve fitting of the observed scattered energy with a standard model, along with a stripping technique to isolate the PKiKP coda from the rest (eg. P, PcP, and PP codas). The coda energy is usually obtained from the mean square of the velocity, but the envelope seems to be more suitable. The selected model consists of an exponential decay in time, which depends upon the quality factor of coda waves (Qc), the geometrical spreading of the scattering medium, and a constant that depends on the general properties of the medium. This model can be easily linearized allowing the use of well-developed least squares techniques. We also apply the Coda Normalization method to remove the source and site effects. Following this procedure, we have been able to isolate and study in detail the PKiKP coda. Our preliminary results show a strong correlation between the different parameters (Qc, the geometrical spreading, and the medium constant), not allowing a definitive interpretation of their numerical values. Nevertheless, the resulting decay rate appears to be clearly distinguishable in each case, permitting a visual comparison. We believe that the detailed study of more events might let us constrain spatial and/or temporal variations in the ICS. Our findings will help in the understanding of the inner core 3D structure and possibly help resolve the issue of the inner core differential rotation.
DE: 8115 Core processes (1507)
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 7207 Core and mantle
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting