The scope of our continuing research is the application of image reconstruction or tomographic techniques to a systematic and rigorous study of the Earth's laterally-heterogenous mantle and core seismic velocity structures. In the course of the initial funding period of this proposal, using a large-matrix, row-action inversion method that was developed, tested and refined during the first stages of our analysis, we have constructed spherically-symmetric, lower-mentle P and S-wave velocity models as well as P and S-wave seismic-station travel- time residual correction sets. We are using travel-time data from the International Seismological Centre's (ISC) short- period, global earthquake catalog. Nearly 2.4 million source- receiver data points from 24,423 earthquakes, representing teleseismic P and S ray paths in the 25o-105o epicentral distance range (bottoming depths from 700 kilometers to the core-mantle boundary) were used in the model inversions. The P results and the S velocity model show significant variation and improvement from results obtained by other studies and the S station correction set is possibly the first usable set ever developed. Using these improved models of both the lower mantle's spherically averaged structure and the upper-mantle and crustal lateral velocity variations as starting models, we are continuing and extending our analysis in a systematic investigation of the structure of the Earth's mantle, outer and inner core and core-mantle boundary.
