9709996 Weidner This proposal is to continue a collaborative project between seismologists and mineral physicists. The project's goal is to increase the understanding of the Earth's upper mantle and transition zone through an integrated, quantitative analysis of seismological and mineralogical data. During the first year of this project, the PIs have completed two collaborative investigations of the fine structure of the 410-km and 660-km phase transitions. These studies demonstrate that some of the details of these transitions predicted by the laboratory data (e.g., finite width) can be resolved by seismic data on frequency-dependent reflection coefficients and triplicated waveforms. Moreover, it appears that the seismic data can constrain model parameters that are only poorly determined in the laboratory. In the next phase of research, they will use a combination of mineralogical and seismological constraints to derive a new generation of regional upper-mantle models that should eliminate some inconsistencies evident in their published models. They will also conduct new seismic experiments to resolve the fine structure of the 410-km, 520-km, and 660-km transitions and use these data to test hypotheses based on refined mineralogical models. ***
