9628051 Vidale This research involves the use of earthquake recordings at dense short-period seismic networks that are analyzed as an array to delineate details of mantle structure, especially at and near the core-mantle boundary and at discontinuities in the upper mantle. Core reflections and refractions recorded at over 1000 seismic stations in the western U.S. from more than 50 large earthquakes in Central and South America will be used to image the heterogeneity near the core-mantle boundary. Approximately 100 Nevada Test Site nuclear tests recorded at west coast stations will be used to analyze reflections from the top of upper mantle discontinuities. P'P' reflections from the bottom of the same discontinuities will also be used as sensitive indicators of sharp changes in upper mantle properties. Study of these mantle heterogeneities and discontinuities will help us learn about the Earth's convection which is the driving force for plate tectonics and earthquakes. This research is a component of the National Earthquake Hazard Reduction Program. ***
