HR: 0800h
AN: DI31A-0251    [Abstracts]
TI: Global Observations of Short Wavelength Topography on The Inner Core Boundary
AU: * Lippman, J D
EM: jdlippman@ucdavis.edu
AF: University of California Berkeley Seismological Laboratory, 215 McCone Hall, Berkeley, CA 94720, United States
AU: Cao, A
EM: acao@seismo.berkeley.edu
AF: University of California Berkeley Seismological Laboratory, 215 McCone Hall, Berkeley, CA 94720, United States
AU: Romanowicz, B
EM: barbara@seismo.berkeley.edu
AF: University of California Berkeley Seismological Laboratory, 215 McCone Hall, Berkeley, CA 94720, United States
AB: Using high quality earthquake doublets from the South Sandwich Islands observed at the Yellowknife array, Cao et al. (2007) found evidence for significant anomalies in the amplitude of the post-critical reflected phase PKiKP, particularly in the frequency band 1-2 Hz, which they interpreted as evidence for short wavelength topography on the Inner Core Boundary (ICB). While the observations reported were limited to a small region of the ICB, an interesting question is whether such topography is globally distributed or presents differences between the eastern and western hemispheres, for which clear differential travel times and attenuation have been reported for these phases. Constraining the nature and lateral variations of the ICB and top of the inner core may help shed light on core dynamics and in particular the generation of the geodynamo. We have now scanned the IRIS database from 1972 to 2005, and assembled a high quality global dataset of waveforms in the distance range 134-144o, for which PKIKP and PKiKP are sufficiently separated to warrant the quantification of amplitude ratios between these two phases. The measured PKIKP/PKiKP amplitude ratio R in the frequency band 1-2 Hz was used to divide the data set into "normal" or "anomalous", for which values of R are larger than the maximum that can be explained by any realistic reference earth model. We found no systematic pattern in the distribution of normal and anomalous observations, both observed throughout the areas sampled by the available distribution of sources and receivers. In particular, there is no hemispherical pattern, indicating that the latter must originate at some depth below the ICB, rather than on the ICB itself.
DE: 7200 SEISMOLOGY
DE: 7207 Core (1212, 1213, 8124)
SC: Study of the Earth's Deep Interior [DI]
MN: 2007 Fall Meeting