HR: 1340h
AN: MR43A-0884    [Abstracts]
TI: Waveform Search for the Innermost Inner Core
AU: * Cormier, V F
EM: vernon.cormier@uconn.edu
AF: University of Connecticut, Department of Physics, 2152 Hillside Road, Storrs, CT 06269-3046 United States
AU: Stroujkova, A
EM: anastasia.stroujkova@uconn.edu
AF: University of Connecticut, Department of Physics, 2152 Hillside Road, Storrs, CT 06269-3046 United States
AB: Waveforms of the PKIKP seismic phase in the distance range 150$^{o}$ to 180$^{o}$ are analyzed for evidence of an inner-most inner core of the type proposed by Ishii and Dziewonski having an abrupt change in elastic anisotropy near radius 300 km. Seismograms synthesized in models having a discontinuity at 300 km radius in the inner core exhibit focused diffractions around the innermost sphere at antipodal range that are inconsistent with observed PKIKP waveforms. Successful models have either a transition in elastic properties spread over a depth interval greater than 100 km or an innermost sphere that exceeds 450 km radius. Evidence of a sharp discontinuity in the lower to mid-inner core is sparse in existing global seismic data. Some examples, however, can be found of PKIKP complexity near 161$^{o}$ and 164-165$^{o}$, consistent with a triplication created by a 475 km radius discontinuity. An abrupt change in either viscoelastic or scattering attenuation at this radius is also observed in PKIKP waveforms, suggesting the existence of an inner-most sphere with low, regionally uniform, seismic attenuation. In contrast to the relatively uniform inner-most inner core, a 0 to 100 km thick region at the top of the inner core exhibits strong lateral variation in seismic attenuation, suggesting lateral variations in the processes of solidification, flow and recrystallzation at the inner core/outer core boundary. Analogous to the evidence for an abrupt fabric change in the upper-most inner core, the seismic evidence for an inner-most inner core may represent another fabric change. This change may simply signify the end stage of solidification, flow and recrystallization, resulting in the highest ordering and largest grain sizes of intrinsically anisotropic crystals.
UR: http://www.phys.uconn.edu/~cormier/innermost.html
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 7203 Body wave propagation
DE: 7207 Core and mantle
DE: 3909 Elasticity and anelasticity
DE: 1015 Composition of the core
SC: Mineral and Rock Physics [MR]
MN: 2004 AGU Fall Meeting