HR: 1340h
AN: T43A-1310    [Abstracts]
TI: Structure of the Inner Core-Outer Core Boundary Inferred From $PKP_{BC}$ Diffracted Waves
AU: * Zou, Z
EM: zouz@eas.slu.edu
AF: Saint Louis University, 3507 Laclede Ave. , Saint Louis, MO 63103 United States
AU: Koper, K D
EM: koper@eas.slu.edu
AF: Saint Louis University, 3507 Laclede Ave. , Saint Louis, MO 63103 United States
AB: Examining the structure of the inner core-outer core boundary (ICB) is important for understanding the evolution and dynamics of the Earth's core. Seismic waves that diffract past the C cusp ($PKP_{Cdiff}$) preferentially sample the ICB and so contain important clues about this region. Just as $P_{diff}$ has been studied to infer core-mantle boundary structure, we expect that analysis of $PKP_{Cdiff}$ will reveal ICB structure. However, there have been few systematic studies of $PKP_{Cdiff}$. We examined all of the IRIS temporary networks for which data are currently available and found three that provide enough high-quality $PKP_{Cdiff}$ data for array processing techniques to be used effectively: INDEPTH-II, INDEPTH-III, and BANJO. We apply the cross-correlation and adaptive stacking techniques to the broadband waveforms to extract the differential travel times of $PKP_{Cdiff}$ across the arrays, and use a weighted least-squares technique to invert theses times for the three-dimensional $PKP_{Cdiff}$ slowness vector. We generate standard errors for the ray parameter and backazimuth using a bootstrap-type resampling algorithm. The earthquakes we analyze at the three networks sample different regions of ICB. For the earthquakes recorded at INDEPTH-II and INDEPTH-III arrays, $PKP_{Cdiff}$ phases sample the ICB beneath north Africa and southwest Europe, and for the earthquakes at BANJO, they sample the ICB beneath Antarctica and west North America. We find $PKP_{Cdiff}$ ray parameters vary from $1.79 \pm 0.11$ to $1.95 \pm 0.05$ s/deg beneath north Africa and southwest Europe,from $1.60 \pm 0.08$ to $1.74 \pm 0.07$ beneath Antarctica and have values around $1.82 \pm 0.09$ beneath west North America. In order to lessen the effect of shallow structure on the travel times, we also invert the differential travel times ($PKP_{Cdiff}-PKP_{DF}$) for differential slowness vectors. We find less variation in them, however the differences appear to be significant. Therefore, our initial results support the idea of modest lateral heterogeneity at the ICB. We intend to examine the robustness of this result by refining our observational technique, quantifying the relationship between $PKP_{Cdiff}$ ray parameters and ICB structure, and identifying more $PKP_{Cdiff}$ phases from regional networks to make a global study of ICB heterogeneity.
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