b. Seismic Reflection Profiling . Seismic reflection profiling is 



a technique widely used for delineating geologic features such as bedding 

 surfaces, faults, rock outcrops, channels, and structures beneath the sea 

 floor. Continuous reflections are obtained by generating repetitive, 

 high-energy, sound pulses near the water surface and at the same time 

 recording "echoes" from the sea floor-water interface and from subbottom 

 interfaces between acoustically dissimilar materials. This is done while 

 the survey vessel is moving. In general, the compositional and physical 

 properties (e.g., porosity, water content, relative density) which com- 

 monly differentiate sediments and rocks also serve to produce acoustic 

 contrasts which show as dark lines on the seismic paper records. Thus, a 

 seismic profile is roughly comparable to a geologic cross section (Fig. 4). 



The seismic reflection data were obtained by towing sound-generating 

 and -receiving instruments behind the Galveston survey boat Voltevt which 

 followed predetermined survey tracklines (Fig. 5). 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 was 

 employed to gain very high resolution of the upper 15 meters of sea floor; 

 an E.G.G., Inc. UNIBOOM system was used to decipher geologic conditions 

 to depths of 40 meters (131 feet) below the sea floor with little sacri- 

 fice in resolution. Data from each system complement each other and are 

 needed to achieve maximum understanding of the subbottom geologic char- 

 acter. A vertical scale on the profiles was determined using a sound 

 velocity of 1,463 meters (4,800 feet) per second in water and 1,645 meters 

 (5,400 feet) per second for typical marine sediments. Additional informa- 

 tion on various seismic profiling techniques is discussed in Ewing (1963) , 

 Moore and Palmer (1967), Barnes, et al. (1972), and Ling (1972). 



c. Coring Equipment . A pneumatic vibratory coring device specific- 

 ally designed to obtain sediment cores a maximum of 6.1 meters long (Fig. 

 6) was used in the phase II survey operation. The apparatus is equally 

 effective in penetrating and recovering granular and cohesive sediments. 

 The core rig consists of a standard 10. 1 -centimeter (4 inches) steel core 

 barrel, clear plastic inner liner, shoe and core catcher, and pneumatic 

 driving head attached to the upper end of the barrel. These elements are 

 enclosed in a tripodlike frame with four articulated legs which rest on 

 the sea floor. The aluminum H-beam and frame serve as a support structure 

 and guide for the vibrator head and core pipe as the core barrel penetrates 

 the sea floor. Detachment of the core device from the surface vessel 

 allows limited motion of the vessel during the actual coring process. 

 Power is supplied to the pneumatic vibrator head by a flexible hoseline 

 connected to a large-capacity (250 cubic feet per minute) air compressor. 

 After coring is completed, the assembly is hoisted on board the vessel, 

 the liner containing the core removed, samples from the top and bottom of 

 the core removed, the ends sealed, and the core is carefully marked for 

 orientation and identification. The historical development of vibratory 

 coring equipment is discussed by Tirey (1972) . 



The self-propelled jack-up barge, Lim Bowman (Fig. 7), was used as 

 the platform for phase II coring. It is 18.3 meters (60 feet) long and 



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