Analysis of Steep Angle Seismic Reflections from Earth's Inner and Outer Core

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Abstract for proposal EAR0087330 (PH # 17x)Title: Analysis of Steep Angle Seismic Reflections from Earth's Inner and Outer CorePI: Keith D. Koper, University of ArizonaThe proposed research focuses on seismic constraints of global variations in topography on the inner core-outer core boundary (ICB) and the core-mantle boundary (CMB). Variations in steep angle (S,P)KiKP-(S,P)cP differential travel times will be used to estimate the ellipticity of the inner and outer core, to search for short-wavelength topography on these boundaries, to provide observational bounds on the homogeneity of the liquid outer core, and to search for evidence of differential rotation of Earth's inner core. Variations in steep angle outer core differential travel times, primarily ScP-PcP, will also be used to quantify global variations in vertical mantle profiles of bulk sound velocity. An unprecedented number of steep angle differential core reflection data are available from the seismicity catalog produced by the prototype International Data Center (pIDC). Approximately 20 of the globally distributed stations that report data to the pIDC consist of arrays of short period vertical component seismometers. Array stations are markedly more sensitive to steep angle core reflections than traditional three component stations, and the azimuth and slowness observations made by array stations greatly reduce phase misidentification. By considering the differential travel times of pairs of such reflections the effects of earthquake mislocation and upper mantle heterogeneity are substantially reduced and seismic structure at the CMB and ICB is revealed.