74 beers. GEOPHYSICAL PROBLEMS [Ch. 4 



tionships existing among the various parameters. It is important to 

 estimate the probable significance of these coupling factors, first, as 

 they are independently established and, then, as they are arranged to 

 show their several relationships. 



The development of a final solution is a series of probability deter- 

 minations. At each successive stage a closer approach to the end 

 result is achieved. With the addition of each sample of new data 

 and the interpretation and correlation thereof, relative priorities of 

 each partial solution become established. The final solution expresses 

 the order of probabilities which the respective solutions bear to one 

 another. One solution may rank very high and be employed as the 

 first working basis. 



This method of attack will stand in sharp contrast to that employed 

 by some engineers and scientific workers. In many fields it is estab- 

 lished practice to formulate a single, explicit, unique solution. The 

 possibility of other solutions is not admitted. In geophysical sciences 

 the number of variables is so large that a single solution cannot be 

 depended on. It is necessary to use the multiple-hypothesis method 

 to be certain that nothing has been overlooked. Sometimes not even 

 this method will cover the field. 



OUTLINE OF GEOPHYSICAL METHODS 



The broad nature of geophysics, as indicated above, requires one 

 to approach the subject slowly. A division can be made into: (1) 

 "pure science" geophysics; (2) exploration geophysics for petroleum 

 and minerals; (3) engineering geophysics (including soil mechanics); 



(4) geophysical aids to geologic mapping, surface and subsurface; 



(5) development of ore deposits; (6) petroleum production — primary 

 and secondary recovery; (7) military and naval problems. 



The advantage of viewing all these areas of interest together is that 

 principles, techniques, and instrumentation developed in one area may 

 find useful applications in others. Borrowing of ideas is important 

 because of the high cost of geophysical research and development. 

 A reflection seismograph used for petroleum exploration may cost 

 $100,000 in capital outlay and an operating charge of $600 per diem. 

 If there is any operating principle, technique, or instrument which the 

 petroleum industry has already developed it is expedient to adapt it 

 to new problems. The cost of geophysical research and development 

 for new problems of sedimentation may be prohibitive. The wisdom 

 of employing expert consultants in study groups is indicated by these 

 costs. The experts bring with them not only a working knowledge 



