Navigational fixes during the seismic survey were obtained about every 2 minutes 

 and each fix was keyed to the seismic records by an event mark on the records. 



b. Seismic Reflection Profiling . Seismic reflection profiling is widely 

 used to delineate geologic features on land and over water. In this study, 

 repetitive high-energy sound pulses were generated near the water surface to 

 produce seismic waves, which reflected off the geologic features; these waves 

 were received and recorded on paper by a recorder aboard the survey vessel to 

 produce a cross section representing the features at and below the lake bottom. 



The seismic reflection data were obtained by towing the sound-generating 

 and receiving instruments behind the DGS research vessel, GS-1 (Fig. 8), which 

 followed predetermined survey tracklines (Figs. 2 to 7). In phase I of this 

 study, two seismic subbottom profiling systems were used simultaneously: an 

 Ocean Research Equipment, Inc. (ORE) 3.5-kilohertz pinger system and an Edgerton, 

 Gremerhausen and Greer (EG&G) , Inc. UNIBOOM system. The pinger records were of 

 little use because of their lack of resolvable reflectors, whereas the UNIBOOM 

 records were generally good. The inshore boundary of the survey was about 1 

 kilometer from shore and the offshore boundary was about 7 kilometers offshore. 

 The nearshore survey water depths were about 7.5 meters, which is about the 

 minimum depth for obtaining good-quality seismic profiles; the offshore water 

 depths were about 14 meters. Information on various seismic profiling tech- 

 niques is discussed in Ewing (1963), Moore and Palmer (1967), Barnes, et al. 

 (1972), and American Association of Petroleum Geologists (1977). 



Figure 8. 



The DGS Research Vessel GS-1 used to tow the seismic 

 equipment and locate core sites. 



