HR: 0800h
AN: S41C-1007    [Abstracts]
TI: A New Method for Constraining Bulk Sound Speed at the Base of the Mantle
AU: * Manners, U J
EM: umanners@ucsd.edu
AF: University of California San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0225 United States
AU: Reif, C T
EM: creif@ucsd.edu
AF: University of California Santa Cruz, Earth Sciences 1156 High Street, Santa Cruz, CA 95064 United States
AU: Masters, G
EM: tmasters@ucsd.edu
AF: University of California San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0225 United States
AB: One of the most distinctive and enigmatic features of the mantle are the slow velocity superplumes at the base of the mantle. However, due to a lack of coverage in the southern hemisphere, it has been difficult to characterise the shear and compressional variations within these regions. Using cluster analysis, we have created a new data set of diffracted waves to improve coverage of the base of the mantle. Our shear and compressional models derived from our data are similar to previous models, with large slow velocity anomalies beneath the Pacific and Africa. In order to determine the cause of velocity anomalies, one can jointly invert P and S data. Conventionally, this is done by solving simultaneously for shear velocity and bulk sound. However, the data are dominantly sensitive to shear velocity and changing the smoothing or parameterisation can change the bulk sound speed significantly. We have developed a technique to directly image bulk sound speed by combining S and P residuals for matching source-receiver pairs to create a `bulk sound speed' residual. These residuals can be plotted to determine the coverage and nature of the signal. As seen in earlier studies, the bulk sound speed residuals are anti-correlated with the shear velocity residuals, but the pattern is now more complex.
DE: 7203 Body waves
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7270 Tomography (6982, 8180)
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
SC: Seismology [S]
MN: Fall Meeting 2005