9417542 Wysession This research is to do seismological mapping of the core-mantle boundary. This boundary is important for models of convection in the mantle and of heat transfer from the core. This work will take advantage of essentially untapped sources of digital data to increase by an order of magnitude the number of direct observations of the core-mantle boundary. A search will be done for digital waveform catalogs to extract and analyze the waveform sets of SKS-SKKS-SHdiff-SVdiff and PKP(DF)-Pdiff phases using a calculation of differential travel times involving reflectivity synthetic seismograms. Differential travel times between diffracted and core phases eliminate most of the spurious source and receiver effects which are similar for both paths. Current 3-D tomographic mantle velocity models will be used to help correct for differences between the degrees of heterogeneity, anomalous differences between the diverging diffracted and core phases in the mantle, and because the outer core is too fluid to maintain high degrees of heterogeneity, anomalous differences between the diffracted and core phase travel times will be interpreted as being due to heterogeneities in D". Variations in the frequency amplitudes of the waveforms will also be analyzed to interpret the velocity structure of the lowermost mantle, as different D" velocity structures affect the SVdiff/SHdiffand SKKS/SKS ratios in different ways. *** ??
