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Use of Multichannel Seismic Systems 



To acoustically penetrate the thick sedimentary sections 

 along the continental margins and record the stratigraphic 

 changes, multichannel seismic systems must be employed. Such 

 systems have long been used by the oil industry, but the enor- 

 mous expense of acquisition, operation of the system, and data 

 processing has limited their application by oceanographic re- 

 search institutions. 



The office of I DOE supported development of a 6-channel 

 seismic system at WHOI. The University of Texas (Galveston) 

 received as a gift a 24-channel system and an office data- 

 processing system. IDOE provided support to both institutions 

 to test these systems at sea. 



WHOI tested their system off Georges Bank in an area 

 where oil companies made survey results (obtained with 24- 

 channel systems ) available as a guide and comparison. This multi- 

 channel seismic system was used in the Georges Bank region to 

 determine the seaward extension of Triassic structures in the 

 Gulf of Maine, the westward extension of diapiric structures 

 on the Scotian shelf, and the relation between the structural 

 ridge on the seaward edge of Georges Bank and the diapiric 

 ridge off Browns Bank. 



Previous seismic studies off eastern North America, to 

 interpret the structure of the basement underlying the con- 

 tinental margin, were restricted to the Gulf of Maine, where the 

 sediment blanket is thin enough to be penetrated by a single- 

 channel seismic system. However, the basement structures sea- 

 ward of the Gulf of Maine are masked by Jurassic-Cenozoic 

 deposits as great as 10 km in thicknessss, too massive to be 

 acoustically transparent to a single-channel seismic system. 



By using a six-channel system, investigators are de- 

 termining whether basement structures of the outer con- 

 tinental shelf resulted from tectonic episodes of faulting and 

 basaltic intrusion during separation of the North American and 

 African continents or from vertical migration of sediments. 

 Seismic survey lines will be extended to Browns Bank on the 

 Scotian Shelf to correlate stratigraphic data from a previously 

 drilled deep hole. Data obtained from this investigation and that 

 obtained earlier in the Gulf of Maine will be used to develop 

 a tectonic model of the North American margin. The data will 

 also be used to compile accurate paleographic maps of the 

 Atlantic region prior to formation of the present Atlantic Ocean. 



The University of Texas (Galveston) tested its 24-channel 

 seismic system in the western Gulf of Mexico as part of an 

 investigation of the deep structure of the Gulf. The collected 



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