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

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EAR-0229103Keith D. KoperThis project will use high frequency seismic waves recorded atseismograph stations of the International Monitoring System (IMS)to map and model the fine structure of Earth's inner core. The sameproperties and techniques that make IMS array stations useful fordetecting and locating nuclear weapons tests make them ideal forobserving the often faint seismic phases that interact withthe inner core. Although the inner core is quite small physicallyit plays a large role with respect to the geodynamo, and moregenerally with respect to heat transfer within the Earth. In thesame sense that ice cores can be used to deduce past climatefluctuations it may be possible to use seismic models of the fineradial structure of the inner core to constrain the history of Earth'smagnetic field.The data gathered from IMS stations will be processed withstandard array techniques such as beamforming, fk analysis, andphase-weighted stacking to observe core reflections (ScP, PcP,PKiKP, SKiKP) and refractions (PKPbc, PKPdf). Relative propertiesamong phases recorded on the same seismogram will be used tomitigate the effect of shallow structure. Specific researchtargets include using PcP/PKiKP amplitude ratios to constrainthe shear velocity at the top of the inner core and the densityjump across the inner core-outer core boundary (ICB), modelingprecritical PKiKP phases to constrain the thickness of the ICB,evaluating the hypothesis of an anisotropic discontinuity beneaththe ICB using quasi-polar PKPbc and PKPdf phases, and evaluatingthe inner-core scattering hypothesis by analyzing the codaof precritical PKiKP phases in the transparent zone.--