title: Short wavelength topography on the inner-core boundary.
abstract: Constraining the topography of the inner-core boundary is important for studies of core-mantle coupling and the generation of the geodynamo. We present evidence for significant temporal variability in the amplitude of the inner core reflected phase PKiKP for an exceptionally high-quality earthquake doublet, observed postcritically at the short-period Yellowknife seismic array (YK), which occurred in the South Sandwich Islands within a 10-year interval (1993/2003). This observation, complemented by data from several other doublets, indicates the presence of topography at the inner-core boundary, with a horizontal wavelength on the order of 10 km. Such topography could be sustained by small-scale convection at the top of the inner core and is compatible with a rate of super rotation of the inner core of approximately 0.1-0.15 degrees per year. In the absence of inner-core rotation, decadal scale temporal changes in the inner-core boundary topography would provide an upper bound on the viscosity at the top of the inner core.
authors.affiliation: Berkeley Seismological Laboratory, University of California, Berkeley, CA 94720, USA.
authors.forename: Aimin
authors.initials: A
authors.lastname: Cao
authors.forename: Yder
authors.initials: Y
authors.lastname: Masson
authors.forename: Barbara
authors.initials: B
authors.lastname: Romanowicz