The geophysical approach to very shallow exploration problems has been limited, in the main, to electrical, magnetic, electromagnetic, and refraction methods. The reflection seismograph, with its clear advantages of decreased ambiguity and increased resolving power, can be applied to many of these problems.In the fall of 1951, a Stanford Research Institute crew conducted an experimental reflection survey in Minnesota, mapping with correlation spreads the glacial drift-bedrock interface along seventy miles of line. The interface varied from a few hundred to several hundred feet in depth below surface, and control core holes showed the seismic profile to be essentially correct, where checked. Over-all velocities, determined by shooting core holes, varied from 3,800 feet per second to 5,500 feet per second. Special instrumentation included a high speed camera and a filter peaked at 100 cps. All shots were fired in the air.The method has obvious applications to mining, engineering, and ground-water problems, and to difficult weathering problems involving thick alluvial, eolian, or glacial debris.

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