SEISMIC METHODS 887 



AIR SHOOTING 



For many years efforts have been made to eliminate the drilling of shot 

 holes for the dynamite charges. Drilling is expensive, due to the high initial 

 outlay for drills and heavy truck equipment. Labor costs are high due to 

 the personnel required for drilling, hauling water, setting casing in many 

 areas, etc. In numerous cases exploration has been abandoned because the 

 shot-points w^ere inaccessible to the heavy rigs, or because of lack of water 

 or the difficulty of drilling through till and boulder material. 



Other methods for producing the elastic waves have been sought, and 

 air shooting has been advocated for a number of years. One of the early 

 suggestions for this technique was made by McCollumf, who desired to 

 create a source of continuous sound which would have a long radius of 

 curvature, i.e., the wave front would be substantially parallel to the surface 

 when it strikes the ground. This was accomplished by placing the source 

 at a considerable elevation above the surface of the earth, using kites or 

 airplanes. 



During 1942 tests to determine the efficacy of exploding dynamite 

 charges above the surface of the earth were reported by Russian geophysi- 

 cists.J The tests were made in salt dome exploration in the Kazak Republic. 

 Best results were claimed when the dynamite charge was positioned at a 

 height of 5 to 7 feet above the surface of the ground. The quantity of 

 explosive was found to be 15 to 20 times greater than that required for the 

 shot hole drilled to the bottom of the low velocity layer. 



The records obtained when the explosive was positioned above ground 

 were comparable in appearance to those obtained when the charge was 

 placed in a drill hole. Air shots were made over many different types of 

 surface rocks and conditions, and in all cases satisfactory seismograms were 

 reported to have been obtained. During 1943 further work was done in the 

 Turkmen Republic. There the explosive was placed only 1.5 feet above 

 ground. The terrain in this area comprises quicksands which are impassable 

 to automotive equipment. It was believed that the cost of the extra dynamite 

 required for air shooting was more than offset by the greater speed of field 

 operations and the lower operating cost per month. 



Developments in the United States 



Considerable work in developing the air shooting technique has been 

 done in the United States by Dr. Thomas C. Poulter, under the facilities of 

 the Southwest Research Institute and the Stanford Research Institute. 

 During the seismic survey of the Ross Shelf ice in the Antarctic§, Poulter 

 found that excellent reflections were consistently obtained with the dyna- 



t B. McCollum, "Method and Apparatus for Studying Geologic Contours," U. S. Patent 

 1,675,121, Tune 26, 1928. 



t A. A. Tsvetaev, "Testing the Application of Air Explosions in Seismic Reflection Explora- 

 tion," Applied Geophysics, No. ], 1945, p. 82-87. Organ of Federal United Geophysical Trust; Scien- 

 tific Research Institution of Applied Geophysics; People's Commissariat of Petroleum, U.S.S.R. 

 (Also reviewed in Geophysics. Vol. XIII, No. 3, July, 1948.) 



§ Second Byrd Antarctic expedition, 1933-35. 



