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DOI	10.2172/883592
Title	FY05 LDRD Final Report The Innermost Inner Core: Fact or Artifact?
Creator/Author	Tkalcic, H ; Flanagan, M P ; Mogri, H
Publication Date	2006 Jan 09
OSTI Identifier	OSTI ID: 883592
Report Number(s)	UCRL-TR-218053
DOE Contract Number	W-7405-ENG-48
DOI	10.2172/883592
Other Number(s)	TRN: US200615%%159
Resource Type	Technical Report
Research Org	Lawrence Livermore National Laboratory (LLNL), Livermore, CA
Sponsoring Org	USDOE
Subject	58 GEOSCIENCES; AMPLITUDES; ANISOTROPY; ATTENUATION; FREQUENCY DEPENDENCE; HYPOCENTERS; P WAVES; QUALITY FACTOR; ROTATION; SAMPLING; SIMULATION; SPECTRA
Description/Abstract	P'P' (PKPPKP) are P waves that travel from a hypocenter through the Earth's core, reflect from the free surface and travel back through the core to a recording station on the surface. Here we report the observations of hitherto unobserved near-podal P'P' waves (at epicentral distance < 10{sup o}) and very prominent precursors preceding the main energy by as much as 60 s. We interpret these precursors as a back-scattered energy from previously undocumented horizontally connected small-scale heterogeneity in the upper mantle beneath the oceans in a zone between 150 and 220 km depth beneath the Earth's surface. From these observations, we identify a frequency dependence of attenuation quality factor Q in the lithosphere through forward modeling of the observed amplitude spectra of the main and back-scattered P'P' waves. In addition, we did not find that travel times corresponding to very polar paths through the centermost inner core with respect to the rotation axis of Earth are anomalously advanced, which argues for isotropic or at best --weakly-anisotropic center of Earth in the direction parallel with the rotation axis. More systematic sampling near Earth's center and characterization of anisotropy in Earth's center will be a subject of future research efforts.
Country of Publication	United States
Language	English
Format	Size: PDF-file: 22 pages; size: 16.6 Mbytes
System Entry Date	2007 Nov 30
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