HR: 1340h
AN: MR23B-0053    [Abstracts]
TI: Deciphering Lower Mantle Structure With the Dispersion of Core-Diffracted Waves
AU: * Euler, G G
EM: ggeuler@wustl.edu
AF: Department of Earth and Planetary Sciences, Washington University in St. Louis, Campus Box 1169, EPSc Room 110, 1 Brookings Drive, St. Louis, MO 63130-4899 United States
AU: Wysession, M E
EM: michael@seismo.wustl.edu
AF: Department of Earth and Planetary Sciences, Washington University in St. Louis, Campus Box 1169, EPSc Room 110, 1 Brookings Drive, St. Louis, MO 63130-4899 United States
AU: Aleqabi, G I
EM: ghassan@seismo.wustl.edu
AF: Department of Earth and Planetary Sciences, Washington University in St. Louis, Campus Box 1169, EPSc Room 110, 1 Brookings Drive, St. Louis, MO 63130-4899 United States
AU: Shore, P J
EM: patrick@seismo.wustl.edu
AF: Department of Earth and Planetary Sciences, Washington University in St. Louis, Campus Box 1169, EPSc Room 110, 1 Brookings Drive, St. Louis, MO 63130-4899 United States
AB: We investigate lateral variations of the D'' region beneath the West Coast of North America using the dispersion signatures of Pdiff and Sdiff waves originating from the Western Pacific Rim. Data come from large earthquakes recorded by over 50 3-component broadband seismic stations stretched across North America as part of seismic networks including the IRIS Global Seismograph Network, U.S. National Seismic Network, Canadian National Seismic Network, and the IRIS PASSCAL Florida-to-Edmonton Seismic Experiment. All data were obtained from the IRIS DMC, resampled at a constant sample rate (20 sps), converted to displacements, and had the instrument responses removed. When the seismic energy of core-diffracted waves occupies a wide frequency band, the structure at the base of the mantle is sampled differently by the energy at various frequencies. The higher-frequency waves stay closer to the core-mantle boundary, while the longer-frequency waves sample more of the lower mantle. This creates dispersion because of the differences in mantle velocities as a function of depth. Using dispersion slowness curves derived from diffracted body waves sampling the thermal and chemical boundary layer region at the base of the mantle, lateral structural variations can not only be resolved but also their nature may be inferred through comparison with synthetic seismic modeling. For this study, the determination of slownesses of incoming diffracted body waves at periods ranging from 150 to 5 seconds was facilitated by an iterative multiple cross-correlation algorithm. Typical results in our calculation of slownesses show r-squared correlations between arrival times and distances above 0.999. We find that dispersion overall causes the slowness to decrease with shorter periods (also found in the synthetic models) and that the dispersion curves we found for different paths resemble the dispersion curves from several different synthetic structural models of D'', thus quantifying the lateral variations in the vertical velocity structure of the base of the mantle.
DE: 3270 Time series analysis (1872, 4277, 4475)
DE: 3909 Elasticity and anelasticity
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005