842 EXPLORATION GEOPHYSICS 



to one of the galvanometer traces to obtain a direct check with the regular 

 timer. 



Miscellaneous tests on the circuits can be conducted. An example is test 

 for cross- feed, for assurance that energy is not being distributed over more 

 traces than expected and thus producing artificial line-up and distorting 

 data. 



Some member of the crew should be familiar with electronic equipment 

 and provided with the necessary test equipment and replacement parts. 



Fig. 527. — Early refraction shot. 



FIELD OPERATIONS IN SEISMIC PROSPECTING 



Early Refraction Shooting. — Refraction shooting was the pioneer 

 method and it is to be expected that the early refraction apparatus and pro- 

 cedure were less refined than those now employed. 



In the early days of refraction seismic work, the shooting was conducted 

 on a time schedule. The clocks of the shooters and recorders were synchro- 

 nized daily, and at definite prearranged times the shooter exploded the 

 charge. Just prior to the shot-times, the various operators, each of whom 

 had a set of seismometers, amplifiers, a recorder, and developing equipment, 

 started the recorders and then allowed them to run for a definite length of 

 time. After getting his record, the operator developed it and then moved 

 to the next station, where the recorder was again set-up for the next 

 scheduled shot. The shooter often remained in one location all day. If for 

 any reason his first shot could not be fired on schedule, he fired it fifteen 



