Annual Report for LDRD-04-FS-019 The Innermost Inner Core: Fact or Artifact?
There is considerable debate in the Earth sciences over the composition, thermal history, and dynamics of Earth's inner core. The details of structural models are based on precious few seismological observations of PKP travel times, due to the uneven distribution of large earthquakes and recording stations around the globe. Using state-of-the-art signal-processing techniques to measure and compile a unique set of global travel time data of surface-reflected seismic waves that propagate through the center of Earth (PKPPKP waves), we propose to investigate the existence of the innermost inner core. We will carry out a systematic investigation to determine the configuration of inner core anisotropy, which is currently biased by a limited spatial sampling of the inner core by PKP waves. We expect to collect data set of waveforms and identify PKPPKP energy arrivals on existing seismological records in a systematic form. We expect to demonstrate whether or not the existence of the innermost inner core can be supported by seismological data and to provide major constraints on the amount of inner core anisotropy. This is a topic of very high interest in the earth science community and the results would be of great importance not only to seismologists but to other Earth scientists as well. This project enhances and extends a critical Laboratory core competency in seismology for national security, specifically for the Ground Based Nuclear Explosions Monitoring Program. This high-profile science project will also support LLNL's mission in basic science by leading to further significant contributions in deep Earth structure, physical properties and models of core evolution. The PI Hrvoje Tkalcic is chairing a special session on the inner core anisotropy at the Fall 2004 AGU meeting, and we will present our results at that session. In FY04, we started systematically downloading a large number of broadband seismic waveforms, available via the Internet from world-wide data centers. These waveforms satisfy our criteria regarding the epicentral distance, event depth and magnitude. We finished extracting all waveforms from global broadband and several regional and temporary networks. We collected data from large earthquakes and explosions. We were focusing on: (1) preparing and analyzing waveforms that satisfy our source-receiver criteria, from 1990 to present day and (2) observing clear PKPPKP arrivals and their precursors in both time and frequency domains. We were also adjusting existing software, modifying it for PKPPKP analysis and building a useful GUI.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 15011810
- Report Number(s):
- UCRL-TR-207235; TRN: US200508%%214
- Resource Relation:
- Other Information: PBD: 14 Oct 2004
- Country of Publication:
- United States
- Language:
- English
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