HR: 0800h
AN: U41B-0402    [Abstracts]
TI: Imaging Lower Mantle Heterogeniety With Differential Dispersion and Attenuation of Core- Diffracted Waves
AU: * Euler, G G
EM: ggeuler@wustl.edu
AF: Washington University in St. Louis, Department of Earth and Planetary Sciences 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: Washington University in St. Louis, Department of Earth and Planetary Sciences Campus Box 1169, EPSc Room 110 1 Brookings Drive, St. Louis, MO 63130-4899, United States
AU: Huhmann, B
AF: Washington University in St. Louis, Department of Earth and Planetary Sciences Campus Box 1169, EPSc Room 110 1 Brookings Drive, St. Louis, MO 63130-4899, United States
AB: We investigate global differential travel-time dispersion and attenuation of core-diffracted phases from large, deep earthquakes. This technique aids in constraining radial velocity structure at the core-mantle interface in a manner analogous to surface wave observables constraining upper mantle structure. We confirm that there is noticeable differential dispersion and attenuation caused by diffraction on a global basis for both Pdiff and Sdiff. Variations in differential dispersion and attenuation are observed with both geographic location and between Pdiff and Sdiff along the same azimuth suggesting lateral variations in Vp, Vs and Vp/Vs ratio in the lowermost mantle. We attempt to utilize dispersion and attenuation characteristics to put bounds on the magnitude and distribution of large-scale velocity perturbations in the lowermost mantle and draw comparisons to variations found in several 3D whole-mantle models. Our dataset consists of broadband records available from the IRIS DMC for deep (>180 km), large (>5.6 mb) teleseismic events. Preprocessing of the records includes deconvolution of the instrument response, rotation of horizontal components, filtering using a set of bandpass filters, and sample-rate decimation (5 sps). Relative arrival times and amplitudes are found by computing cross correlegrams in the frequency domain, detecting and removing poor recordings with cluster analysis, and iteratively converging on a stable low-variance solution with a weighted least-squares inversion while automatically remediating phase-skips utilizing a database of potential relative arrivals. Raypath-approximated corrections for reciever-side differences in ellipticity, mantle, and crust are applied for the derivation of phase velocites in the lowermost mantle as a function of azimuth and frequency. Following previous studies of diffracted signals, we limit our analysis to station pairs located in narrow azimuthal windows spread over a considerable distance while attempting to quantify the acceptable range of aspect ratios. This method has the advantage of removing source-side effects, averaging out minor timing errors, and, for our analysis, averaging out receiver-side frequency-dependent upper mantle and crustal biasing. Comparison with 1D reflectivity and 3D SEM synthetics facilitates our quantitative analysis of the lateral and vertical variations in the seismic velocity structure near the core-mantle boundary region.
DE: 7203 Body waves
DE: 7207 Core (1212, 1213, 8124)
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7260 Theory
DE: 7290 Computational seismology
SC: Union [U]
MN: 2007 Fall Meeting