706 



ELECTRICAL METHODS 



[Chap. 10 



A. 



4» 



HtrittnM Junsaie Covtr 



Fig. 10-46. Determination of strike of steeply 

 dipping shale beds in Normandy, France (after 

 Schlumberger). 



2. Structural studies. Equipotential-line 

 studies have been applied to structural 

 problems for determinuig strike of for- 

 mations under over-burden. Fig. 10- 

 45 shows elliptical equipotential surfaces 

 on dipping Silurian shales, interbedded 

 between Armorican and May sandstones, 

 and covered by Jurassic beds 200 to 

 300 feet thick. This survey was made 

 to determine strike and to trace a siderite 

 deposit on the footwall of the Silurian 

 shales. 



3. Military applications. The equipo- 

 tential-line method may be useful for the 

 location of iron and steel objects in civil 

 and military engineering problems. Fig. 

 10-46 shows an application of this 

 kind to the location of a buried ammuni- 

 tion magazine whose depth was about five 

 feet. 



Following his model 

 experiments with equi- 

 potential-line methods, 

 Fujita conducted exten- 

 sive studies of the poten- 

 tial distribution on the 

 Suwa mine, 100 miles 

 northeast of Tokyo. This 

 mine is operating a large 

 vein of cupriferous pyrite 

 in schists on six levels at 

 100-foot intervals to a 

 depth of 700 feet below 

 the surface. The experi- 

 ments were chiefly con- 

 cerned with various ar- 

 rangements of the line 

 electrodes and attempts 

 to derive the dip of the 

 ore body (70°) from the 

 relative disposition of the 

 anomalous areas. 



Fig. 10-46. Location of a 

 buried ammunition magazine by 

 equipotential methods (after 

 Ebert). 



