has been taken for every 7 miles of geophysical survey. The cores are 3 

 or 4 inches in diameter, and are taken with a pneumatic vibrator-hanraier 

 driving the coring device. Core length ranges from a few inches to 20 

 feet depending on the nature of the materials penetrated. 



The average core length of about 12 feet is adequate for most sand 

 inventory purposes; however, for foundation work and for scientific pur- 

 poses, it is most desirable to sample deeper reflectors. At times deeper 

 reflectors can be sampled by routing tracklines around a site where deep 

 borings have been made in the past. For example, during sand inventory 

 surveys off Virginia and New York, lines run to the Chesapeake and Ambrose 

 light towers permitted use of data obtained in foundation studies made 

 for the construction of these towers. It is also frequently possible to 

 trace moderately deep reflectors on the geophysical profiles to points 

 where they crop out or come within range of the corer at a high point on 

 the reflector or a low point in the bottom. 



4. Data Analysis 



At the conclusion of field survey work all data must be 

 assembled for processing, analyzed, and reduced to a report detailing 

 the findings. The ultimate aim of each regional survey is to produce a 

 report, or series of reports, dealing with the location and nature of 

 sand deposits within the framework of a general exposition of pertinent 

 aspects of the regional geography and geology, bottom morphology, sedi- 

 ment distribution, and subbottom structure. The more immediate task, 

 however, is to provide Corps of Engineers District Offices for planning 

 purposes brief, informal reports concerning sand deposits in areas where 

 Federal Beach Erosion Control or Hurricane Protection projects are pending 

 or authorized. 



a. Seismic Records 



One of the most difficult problems associated with analysis 

 of a large quantity of seismic reflection profiles is their printout 

 size. A 9-inch wide record covering 10 miles of trackline may be 25 to 

 50 feet long. As many as 40 such records may be produced in one grid 



area. 



To lay out two or three of these records side by side for comparative 

 analysis is not only cumbersome, but requires considerable space. There 

 are several other difficulties v\^hich arise when comparing the raw records. 

 Parallel records in a grid set will have been run on opposing ship head- 

 ings; consequently- the various bottom and subbottom features for adjacent 

 tracks are mutually reversed. Further, because of differences in the 

 vessel speed the horizontal scale is not constant either along a single 

 line or from line to line. An added problem arises with records run in 

 comparatively shallow water. If the water depth is less than the effec- 

 tive depth of subbottom penetration multiple reflections of bottom and 

 subbottom acoustic interfaces will be superimposed on the record and 

 may partially mask subbottom detail. Although the true reflectors can 



A-9 



