9405542 Sheehan This research is to make seismic estimates of the sharpness and depth distribution of mantle discontinuities which are important for constraining models of composition and temperature in the Earth. Most measurements of this type have been made at sparsely distributed global stations with significant lateral averaging. However, the combined broadband array available from an upcoming PASSCAL broadband deployment in the Colorado Plateau and Basin and Range, integrated with existing broadband data from the western U.S., provides a unique opportunity for high resolution imaging of mantle discontinuity structure spanning the Basin and Range, Colorado Plateau, Rocky Mountains, and Great Plains physiographic provinces. Knowledge of the details and variations in mantle discontinuity structure across this large region is crucial in determining the thermal and chemical structure of the upper mantle and helping to answer fundamental questions regarding continental evolution and the nature of transitions between the physiographic provinces sampled. ***
