822 EXPLORATION GEOPHYSICS 



through the record drying compartment. This type of dryer practically 

 eliminates the delays occasioned by cold weather and high humidity. 



Three large mouthed one-gallon thermos jugs are placed in the lower 

 cabinet. These jugs contain the developer, stop bath, and hypo solutions. 

 A small red lamp provides a means for inspecting the developing. Over 

 the front of the cabinet is a black opaque cloth cover which is provided 

 with two light-tight armholes and a small red observation window. The 

 operator conducts the developing and fixing operations by inserting his 

 arms through the armholes. Equipment of this type will handle the 

 records of a fast working party conveniently and allow inspection of the 

 records at each set-up without undue loss of operating time. 



INSTRUMENTAL ANALYSIS 



The seismic wave arriving at the surface is a complex wave, con- 

 taining many frequency components. As previously mentioned, the visual 

 analysis of seismic records necessitates considerable filtering to remove 

 certain components so that the frequencies passed by the filter will more 

 clearly show the desired correlation, and also have more "eye-appeal." 

 The characteristics of an optimum filtering system will depend upon the 

 nature of the subsurface materials, the depth to the geological horizons 

 of current interest, and the overall frequency response of the associated 

 equipment. The degree of filtering is rather arbitrary or rule of thumb, 

 and is usually determined by the crew chief on the empirical basis of 

 obtaining records that appear to indicate the best correlation at the depth 

 and for the other conditions believed to be of major importance at the time. 

 If, later, exploratory interest changes : for instance, centers on a deeper 

 horizon, it often is necessary to re-shoot the area to obtain records with 

 the greatest "character" at that depth range. Some organizations are 

 partially overcoming this condition by dual recording, wherein one bank 

 of galvanometers (usually 10 or 12 traces) will record through one filter 

 setting, while the other bank is recording through a different filter setting. 



One solution to the problem of filtering lies in recording the complex 

 seismic wave with high-fidelity equipment which will preserve the full 

 components of the received wave motion on a reproducible record. Studies 

 of the area may then be made as desired merely by playing back the record 

 and varying the electrical parameters to give the desired data. The play- 

 back may involve studies of : the effects of filtering ; the combination of 

 traces under various phase relationships to achieve directional effects ; 

 the frequency analysis of the complex wave to determine its various wave 

 components ; or the frequency pattern. 



A high-quality recording system such as those used for sound recording 

 on motion picture film, magnetic wire, or tape may be employed for the 

 recording of the seismic wave. One very important requirement in this 

 connection is that the film or tape be moved past the scanning point at a 

 uniform rate in order to avoid flutter or "wow," which would result in 



