Seismic refraction studies in the Transcontinental Geophysical Survey

The Transcontinental Geophysical Survey (TGS) was proposed in 1962 as one of the main elements of the U. S. program for the Upper Mantle Project. The TGS is a band 4° (about 275 miles) in width, centered in latitude 37°N, extending from coast to coast and into the Atlantic and Pacific ocean basins. Studies in this band include the whole range of geophysical and geological subdisciplines. The efforts to achieve complete geological, gravity, magnetic, and seismic coverage (as well as selected special observations, such as heat‐flow measurements) are concentrated in the ‘inner band’ (35°‐39°); special studies in the ‘outer bands’ (33°–35° and 39°–41°) will be related to the over‐all program of the TGS (see Figure 1). A general description of planning and programs for the TGS is given by Hart [1964] and in IG Bulletin 87 [1964]. In May 1964, the International Upper Mantle Committee adopted five programs of interdisciplinary studies for emphasis during the Upper Mantle Project, including “combined geophysical‐geochemical‐geological surveys … seismic, gravity, geomagnetic, geothermal, geological, and geoehemical (especially the distribution of radioactive elements) investigations in the same area.”