Seismological Structure of the Inner Core and Core-Mantle Boundary

University Of Washington, Seattle WA

Investigators

Abstract

Abstract for proposal EAR0003557 (PH #7x) Title: Seismological Structure of the Inner Core and Core-Mantle Boundary PI: Kenneth C. Creager, University of Washington We propose to apply well developed and new methods to global digital data to examine the anisotropic and isotropic structure of the inner core and lowermost mantle. We plan to analyze waveforms and differential travel times of five distinct compressional waves (PKPAB, PKPBC, PKPCD, PKPDF, and scattered phases) that propagate through the Earth's core to examine the large-scale variability of elastic anisotropy within the inner core and scattering at the base of the mantle. We will also investigate the boundary layers at the top of the inner core and the bottom of the outer core. In addition, we will apply a new, recently developed method to explore azimuthal anisotropy at the base of the mantle. Results to date suggest strong anisotropy beneath southeastern Australia, perhaps associated with the hotspot near Tasmania. Large-scale lateral variations in the inner core seem to be entirely associated with anisotropy, while the mantle exhibits a combination of isotropic and anisotropic variability. Because the viscosity of the inner is many orders of magnitude less than the mantle, it cannot support significant large-scale lateral variations in density. Because the mechanisms that change density (temperature and chemistry) are the same as those that change isotropic wave speeds, isotropic heterogeneity within the inner core should indeed be small. Two other new proposed projects explore the fine structure of the lowermost mantle using ScP and PKP precursors as probes.