As a result of previous NSF support, this research project has developed a set of over 10,000 measurements of PP-P and SS-S long-period differential travel times . Work on this data set to date includes a description of the various factors affecting the data and an examination of the correlation of the measurements with 3-D models and tectonics. Based on these software and data gathering efforts, new experiments on different seismic phases and 3-D inversions for mantle structure will be done. This work is an obvious and needed extension of previous NSF-supported research. This research has important application to the 3-D determination of mantle seismic velocities which are used as constraints in dynamic models of convection, the driving force of crustal distortion and earthquakes. It therefore is a contribution to the National Earthquake Hazard Reduction Program.
