b. Seismic Reflection Profiling. Seismic reflection profiling is a technique widely used 

 for delineating subbottom geologic structures and bedding surfaces in sea floor sediments 

 and rocks. Continuous reflections are obtained by generating repetitive, high -energy, sound 

 pulses near the water surface and recording "echoes" reflected from the sea floor-water 

 interface, and subbottom interfaces between acoustically dissimilar materials. In general, the 

 compositional and physical properties (e.g., porosity, water content, relative density) which 

 commonly differentiate sediments and rocks also serve to produce acoustic contrasts which 

 show as dark lines on the geophysical paper records. Thus, an acoustic profile is roughly 

 comparable to a geologic cross section. 



Seismic-reflection surveys of marine areas are made by towing variable energy and 

 frequency sound-generating sources and receiving instruments behind a survey vessel which 

 follows the predetermined survey tracklines. The energy source used for this survey was a 

 50- to 200-joule sparker. For continuous profiling, the sound source is fired at a rapid rate 

 (usually 4 pulses per second) and returning echo signals from sea floor and subbottom 

 interfaces are received by an array of towed hydrophones. Returning signals are amplified 

 and fed to a recorder which graphically plots the two-way signal travel time. Assuming a 

 constant velocity for sound in water at 4,800 feet per second and for typical shelf sediments 

 of 5,440 feet per second, a vertical depth scale was constructed to fit the geophysical 

 record. Geographic position of the survey vessel is obtained by frequent navigational fixes 

 keyed to the record by an event marker. Navigation for this project was achieved by use of 

 the Alpine Precision Range System, Model 4350. 



More detailed discussions of seismic profiling techniques can be found in a number of 

 technical publications. (Ewing, 1963; Hersey, 1963; van Reenan, 1963; Miller, Tirey and 

 Mecarini, 1967; Moore and Palmer, 1968; Barnes, et al., 1972; and Ling, 1972.) 



c. Coring Techniques. The sea floor coring device used in this study is a pneumatic, 

 vibrating piston coring assembly designed to obtain core samples (20-foot maximum length; 

 4-inch diameter) in Continental Shelf granular -type sediments. The apparatus consists of a 

 standard steel core barrel, plastic inner liner, shoe and core catcher, with a pneumatic 

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

 tripod-like frame with articulated legs, allowing the assembly to rest on the sea floor during 

 the coring operation. The detached state of the core device from the surface vessel has the 

 advantage of allowing limited motion of the vessel during the actual coring process. Power is 

 supplied to the pneumatic vibrator head by means of a flexible hoseline connected to a large 

 capacity, deck-mounted air compressor. After coring is complete, the assembly is winched 

 on board the vessel; the liner containing the core is removed, capped at both ends and 

 marked and stored. A review of the historical development of vibratory coring equipment is 

 discussed by Tirey (1972). 



