Mapping the Fine Structure of Earth's Inner Core with Seismic Array Data

Saint Louis University, Saint Louis MO

Investigators

Abstract

EAR-0229103 Keith D. Koper This project will use high frequency seismic waves recorded at seismograph stations of the International Monitoring System (IMS) to map and model the fine structure of Earth's inner core. The same properties and techniques that make IMS array stations useful for detecting and locating nuclear weapons tests make them ideal for observing the often faint seismic phases that interact with the inner core. Although the inner core is quite small physically it plays a large role with respect to the geodynamo, and more generally with respect to heat transfer within the Earth. In the same sense that ice cores can be used to deduce past climate fluctuations it may be possible to use seismic models of the fine radial structure of the inner core to constrain the history of Earth's magnetic field. The data gathered from IMS stations will be processed with standard array techniques such as beamforming, fk analysis, and phase-weighted stacking to observe core reflections (ScP, PcP, PKiKP, SKiKP) and refractions (PKPbc, PKPdf). Relative properties among phases recorded on the same seismogram will be used to mitigate the effect of shallow structure. Specific research targets include using PcP/PKiKP amplitude ratios to constrain the shear velocity at the top of the inner core and the density jump across the inner core-outer core boundary (ICB), modeling precritical PKiKP phases to constrain the thickness of the ICB, evaluating the hypothesis of an anisotropic discontinuity beneath the ICB using quasi-polar PKPbc and PKPdf phases, and evaluating the inner-core scattering hypothesis by analyzing the coda of precritical PKiKP phases in the transparent zone. --