HR: 16:00h
AN: T14B-01 INVITED     [Abstracts]
TI: VQM3DA Global velocity, quality factor, and anisotropy models of the lower mantle
AU: * Lawrence, J F
EM: jfisher@levee.wustl.edu
AF: Scripps Inistitute of Oceanography, Institute of Geophysics and Planetary Physics Scripps Institution of Oceanography University of California San Diego , La Jolla, CA 92023 United States
AU: Wysession, M E
EM: michael@wucore.wustl.edu
AF: Washington University, Campus Box 1169 One Brookings Drive, St Louis, MO 63130 United States
AB: We invert over 90,000 differential travel-time and attenuation measurements for 3D whole-mantle velocity (V) and quality factor (Q) models with identical resolution. By comparing models of velocity and quality factor obtained from measurements of SH and SV waves, we calculate velocity anisotropy and quality factor anisotropy. The resolution of each model increases with depth, making them ideal for examination of the lower mantle. High V, Q, and anisotropy are observed beneath subduction zones around the Pacific. Low V, Q, and anisotropy are observed within the lower mantle underlying the Pacific and Africa. The Pacific superplume extends from the core to the surface while the African superplume is limited to the lower mantle. The largest anomalies - both high and low - are observed within the lowermost mantle. The high correlation between upper and lower mantle anomalies suggests that D" has a strong influence on mantle convection. The observed seismic anomalies are indicative of the dominant rheology in the mantle. From strong anisotropy and low attenuation we infer that dislocation creep is the dominant deformation mechanism underlying subduction zones. The low anisotropy and high attenuation of the superplumes indicate that diffusion creep may be dominant in upwellings. The locations of hotspots are highly correlated with both low V and low Q in both the transition zone and the lowermost mantle. These anomalies are likely thermal in nature due to the correlation between V and Q. These anomalies may also have lower viscosity as inferred from the similar temperature dependencies of Q and viscosity. Likewise, the high V and Q anomalies around the Pacific are inferred to be cold, high viscosity slabs.
DE: 8180 Tomography
DE: 5144 Wave attenuation
DE: 7200 SEISMOLOGY
DE: 7203 Body wave propagation
DE: 7207 Core and mantle
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting