HR: 0830h
AN: S31D-0792    [PDF]
TI: On the Existence of Seismic Discontinuities in the Inner Core
AU: * Leyton, F
EM: leytonfo@eas.slu.edu
AF: Saint Louis University, Dept. EAS 3507 Laclede Ave, St. Louis, MO 63103 United States
AU: Koper, K D
EM: koper@eas.slu.edu
AF: Saint Louis University, Dept. EAS 3507 Laclede Ave, St. Louis, MO 63103 United States
AU: Zhu, L
EM: lupei@eas.slu.edu
AF: Saint Louis University, Dept. EAS 3507 Laclede Ave, St. Louis, MO 63103 United States
AU: Dombrovskaya, M
EM: dombrom@slu.edu
AF: Saint Louis University, Dept. EAS 3507 Laclede Ave, St. Louis, MO 63103 United States
AB: We evaluate the possibility of seismic discontinuities within the inner core using a data set of precritical PKiKP waveforms assembled during a previous study. Recent work has suggested the presence of such structures within the inner core, relating them to either changes in anisotropy at shallow depths or at deeper locations. Another explanation is the existence of a crust below the inner core boundary and a low velocity zone, based on geophysical models of inner core growth. Because any phase reflected from a discontinuity within the inner core will have a very small amplitude, we combine source and receiver stacks in our search. For a given event we use cross-correlation to align the data from a short-period, small-aperture seismic array and then construct a receiver stack using linear summation. Next we use one of two procedures (deconvolution by an empirical source time function and envelope formation) to eliminate the signature of the source from each receiver stack. Finally, we stack the receiver stacks from each event using time shifts appropriate for a velocity model with a discontinuity at some depth below the inner core-outer core boundary. We compare the results with synthetic computations done by means of generalized ray theory and appropriate attenuation operators. We perform resolution tests to determine our capability of finding these types of structures, varying the impedance contrast, position of this discontinuity and attenuation inside the inner core. Our results show that the inner core lacks a sharp (thickness less than 4-5 km) global transition to at least 700 km below the boundary with the outer core.
DE: 5430 Interiors (8147)
DE: 7203 Body wave propagation
DE: 7207 Core and mantle
DE: 8115 Core processes (1507)
DE: 8124 Earth's interior--composition and state (old 8105)
SC: Seismology [S]
MN: 2003 Fall Meeting