Topography of Earth's Inner Core Boundary
Abstract
Lateral variations in the structure and crystallization of the inner core will likely be associated with lateral variations in the topography of its boundary. Depending on liquid fraction and the ratio of solid over liquid viscosity, the process of compaction of solids and expulsion of fluids at the solidifying boundary can be dynamically unstable, resulting in small-scale corrugations of the boundary of 0.1 to 5 km height with a horizontal scale on the order of 1 to 10 km. Evidence of such ICB topography has been inferred from waveforms of PKiKP doublets (1). An additional observation consistent ICB topography includes the seismic wave diffracted around the top of the inner core (PKP-Cdiff), whose travel time agrees with that predicted by the AK135 Earth model, but whose amplitude decays more rapidly into the inner core shadow than is predicted by AK135 (2). These observations are modeled by synthesizing seismic body waves with a pseudospectral method (3) having a densified grid in the vicinity of a rough ICB. Validation of the forward modeling includes a comparison of results obtained with a boundary element method. Modeled spectra of ICB topography are used to constrain the parameters and processes that produce the topography. These include compaction length (assuming freezing upward from below), the structure of precipitated piles (assuming metallic snow falling from above), the sedimentary processes due to flow in the overlying F-layer of the outer core, and the relaxation of topography from viscous deformation of the inner core. 1. Cao, A., Y. Masson, and B. Romanowicz, PNAS, 104, 31-35, 2007. 2. Zou, Z., K. Koper, and V.F. Cormier, J. Geophys. Res., 113, 2008. doi: 10.1029/2007JB005316. 3. Furumura T., B.L.N. Kennett, and M. Furumura, Geophys. J. Int., 135, 845--860, 1998.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMDI51B2141C
- Keywords:
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- 5430 PLANETARY SCIENCES: SOLID SURFACE PLANETS / Interiors;
- 7203 SEISMOLOGY / Body waves;
- 7207 SEISMOLOGY / Core;
- 7290 SEISMOLOGY / Computational seismology