strata. The chart is tied to accurately measured shot hole locations since 

 precision in locating geologic features is of considerable importance. Thus, 

 there are usually accurate maps of the shot hole locations. It is unusual, 

 however, for the land manager to receive such a chart as a matter of routine. 



Thumping, a process by which trucks drop heavy steel weights to the ground, 

 is sometimes used in place of explosive charges. Another technique, shaking, 

 was developed by scientists with Sinclair Research. This procedure, which they 

 called "dinoseis," uses a controlled explosion inside a heavy mass, transferring 

 a rapid pulse rich in high frequencies to the ground (Oil and Gas Journal, 

 1964). 



Both methods require some clearing of vegetation for vehicle passage and 

 geophone placement after surveyors have staked the survey line. After the 

 thumping has taken place, geophones are retrieved and the entire operation 

 moves to the next station until the entire line has been traversed. Since the 

 seismic-producing devices are self contained, there is no need for postoperation 

 removal and filling of holes. Thus, there are fewer traverses of the survey 

 line than for explosive methods. These methods work best with dry soils. 



Site-specific geophysical surveys - water areas. Water is a good medium 

 for transferring seismic pulses. Until a few years ago, explosive charges were 

 set off in shallow waters in much the same manner as described above for explo- 

 sive methods. Explosions often stunned or killed aquatic life (St. Amant, 

 1971). Consequently, other devices - sparkers, propane-oxygen guns, air guns, 

 and vibrators - were designed that emitted high frequency pulses not destructive 

 to aquatic life. In areas of soft sediments, cores are cut for characterizing 

 shallow strata. 



In places accessible by boat or marsh buggy, there are few effects on the 

 environment from the nonexplosive methods. Other areas may necessitate overland 

 access to the water body. Here vegetation may have to be cleared and a temporary 

 boat launching ramp may have to be cut through the bank. In order to locate 

 shot points precisely on a map, electrical navigation equipment - small transmit- 

 ters - may be placed at points near the water's edge for precise triangulation. 

 Placement of these devices may require minor clearing. 



Movement of the vessel back and forth to shore for equipment and crew 

 changes or retrieval may result in slightly increased temporary erosional 

 processes at the docking point. Overall, however, the effects of geophysical 

 surveys are minor in shallow-water environments, since the application of the 

 technique is indirect. The most noticeable effects may be in the transporting, 

 launching, and retrieval of the vessel. 



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