738 



ELECTRICAL METHODS 



IChap. 10 



In many instances faults have been located by the resistivity contrast 

 of the formations on either side, or by the effect of the fault itself resulting 

 from highlj^ mineralized waters in the fault plane/^ Structural investiga- 

 tions with resistivity methods are often facihtated by tracing certain key 

 beds of high or low resistivity. An example is the survey of the Bibi- 



3KXf- 



^arw- 



MBypsum MRedbeds; shale 



MLimest. \n\Salt Harry Aurand 



Fig. 10-68. Results of electrical vertical drilling with single-probe method, and 

 corresponding geologic section in an area in New Mexico. 



Eibat anticline near Baku and is of in- 

 terest because measurements were made 

 at the bottom of the sea. A tri-conduc- 

 tor cable with three electrodes was 

 dragged along the sea bottom, the fourth 

 electrode being a fixed ground on land. 

 The key bed in this area (Apsheron 

 limestone) could be clearly noted in the 

 resistivity curve. 



The possibility of electrical salt dome 

 location was demonstrated at an early 

 date by Schlumberger and his associates.^ 

 In 1926 and 1927 the salt domes of 

 Meyenheim and Hettenschlag in Alsace- 

 Lorraine were found by resistivity map- 

 ping. They appeared as resistivity lows, 

 contrary to what would be expected. The lows result from the occur- 

 rence of highly conductive marls above the salt which in turn are cov- 



FiG. 10-69. Equiresistivity con- 

 tours (ohm-meters) on a salt 

 dome in the Emba District, Rus- 

 sia (after Schlumberger). 



*8Hubbert, op. ciL, 40-47. 



" A.I.M.E. Geophys. Pros., 127 (1934). 



"G. Carrette and S. F. Kelly, A.I.M.E. Geophys. Pros., 211-220 (1929). 



