HR: 11:20h
AN: U41C-05    [PDF]
TI: Global Lower Mantle Velocity, Attenuation, and Anisotropy from Differential {\it ScS-S} Analysis
AU: Portle, T R
EM: tportle1@ithaca.edu
AF: Earth and Planetary Sciences Washington University, Campus Box 1169 One Brookings Drive, St Louis, MO 63130 United States
AU: * Lawrence, J F
EM: jfisher@levee.wustl.edu
AF: Earth and Planetary Sciences Washington University, Campus Box 1169 One Brookings Drive, St Louis, MO 63130 United States
AU: Wysession, M E
EM: michael@mantle.edu
AF: Earth and Planetary Sciences Washington University, Campus Box 1169 One Brookings Drive, St Louis, MO 63130 United States
AB: We obtained more than 40,000 high-quality radial and tangential {\it ScS-S} differential travel-time and attenuation residuals. This examination used broadband seismic station data from both permanent global networks (e.g. GSN) for broad sampling and temporary Passcal-style networks for fine resolution of isolate regions between 1990 and 2001. We used these results to explore the elastic and anelastic behavior of the lowermost mantle. Travel-time and attenuation anomalies are often anisotropic and/or correlated, indicating complex structures on various spatial scales. We inverted for seismic velocity and quality factor anomalies on global and regional scales. Resultant models may help differentiate between chemical, thermal, and structural anomalies. The observed mean global differential attenuation varies with epicentral distance, and could only be modeled by adding highly attenuating material at the core-mantle boundary (CMB). Significant deviations from mean lower mantle quality factor and velocity are required to account for the observed seismic anomalies. Observed correlation between seismic velocity and quality factor may indicate regional thermal anomalies. Alternatively, the lack of attenuation variation in the presence of seismic velocity anomalies may indicate chemical or phase variations. Other areas are strongly anisotropic with the absence of strong isotropic velocity and attenuation variations, indicating possible flow or fabric variations. We examine the pattern of velocity, quality factor, and anisotropy to obtain an improved image of the lowermost mantle. Simultaneous examination of the elastic and anelastic characteristics of the lowermost mantle helps differentiate between types of anomalies. Examination of lateral variations on the global scale is consistent with whole-cell convection, while regional examinations provide evidence for isolated small-scale anomalies, which may indicate plume-like activity.
UR: http://epsc.wustl.edu/seismology/jfisher/DDP
DE: 7203 Body wave propagation
DE: 7207 Core and mantle
DE: 7260 Theory and modeling
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 8180 Tomography
SC: U
MN: 2003 Fall Meeting