9305035 Humphreys This research is a continuation of a collaborative effort of four universities to use the PASSCAL portable broad-band seismometer array facility for a comprehensive imaging study of the lateral transitions in mantle structure beneath the Rocky Mountain Front. Field work was completed under the first grant and this will complete the analysis and synthesis of the data. The Front Range of the Colorado Rockies marks the eastern boundary of heavily tectonized western North America and the western physiographic boundary of the stable continental interior. Earlier studies show that there is a major lateral transition in seismic velocities across the Front Range transition, but its details are poorly understood. Understanding this transition will provide constraints on models of western U.S. dynamics and evolutionary models of the North American craton. ***
