Seismology of the continental crust and upper mantle

More seismological studies of the continental crust and sub‐crustal lithosphere of the United States have been completed in the past four years than at any other similar period, and a continued growth in activity is likely to continue for years to come. Several trends account for this phenomenon. First, the interest in seismic reflection studies generated initially by COCORP results in this country [Brown and others, 1986], and later by the British BIRPS results [Matthews and Gheadie, 1986], has led to the development of several other seismic reflection programs. Among the most active of these research programs are those of the University of Wyoming [Smithson and others, 1986], Virginia Polytechnic Institute, CALCRUST [Henyey, 1986], and the U.S. Geological Survey (USGS) [Hamilton, 1986]. In Canada, the Lithoprobe program has achieved remarkable results in a variety of geographic locations [Green et al., 1986]. A second trend is the resurgence of interest in seismic‐refraction/wide‐angle reflection profiling. The year 1978 marked the beginning of this increased activity when several large projects were conducted in the western U.S., such as the Yellowstone‐Snake River Plain experiment organized by the University of Utah. Since 1979, a large amount of refraction/wide‐angle reflection data has been collected by the USGS and by university groups utilizing large numbers of state‐of‐the‐art industry seismographs in cooperative experiments. A third trend is the increased sophistication of other seismic methods such as teleseismic delay‐time methods, tomography, and receiver‐transfer functions. In these studies, permanent or temporary recording arrays have been used to determine local and regional crustal and upper‐mantle structure with impressive resolution.