Upper mantle structure of midwestern United States

Body-wave observations from nuclear events at the Nevada Test Site and several earthquakes near the western edge of the United States have been used to construct a model of the upper mantle along profiles extending toward the Great Lakes. The Cagniard-de Hoop technique for computing synthetic seismograms for laterally homogeneous earth models was used to fit both the amplitudes and travel times of the observations. The model obtained exhibits a prominent low-velocity zone, sharp discontinuities of velocity at about 430 and 660 km, and a discontinuity in the slope of the velocity at about 550 km.