The subsequent sections briefly summarize present methods of inter- 

 preting a continuous seismic profile record, emphasizing those properties 

 of the acoustic record of value to the marine construction engineer. 



DATA INTERPRETATION - QUALITATIVE 



The reflected acoustic signal from the seafloor and the subbottom 

 horizons is a function of the reflectivity, or reflection coefficient, of 

 the particular contact, i.e., 



£ - * - P2 v 2 : P1 V (2) 



Ai p 2 V 2 + PlVi 



where A r = amplitude 01 reflected signal (dynes /cm ) 



Ai = amplitude of incident signal (dynes/cm^) 



pi = saturated bulk density of medium 1 (gm/cm J ) 



P2 = saturated bulk density of medium 2 (gm/cm- 5 ) 



V-i = compressional velocity of sound medium 1 (cm/sec) 



V 2 = compressional velocity of sound medium 2 (cm/sec) 



R = reflection coefficient 



Thus, the amplitude of the signal reflected from the bottom and subbottom 

 strata is a function of the bulk density and velocity of sound in the 

 adjacent lavers. 



The quantity of pV is termed the acoustic impedance, Z, of the material, 

 i.e., 



Z n = Pn v n (3) 



Z]_ = acoustic impedance of medium 1 (gm/cm^sec) 

 Z 2 = acoustic impedance of medium 2 (gm/cm^sec) 

 therefore 



Z 2 + Z-l 



If the contrast in acoustic impedances of two adjoining lavers is 

 great as, for example, in a hard bedrock-sediment contact, a strong reflec- 

 tion is generated. A change in grain size detected in cores, however, may 

 not necessarily cause an acoustic contrast sufficient to be recorded by 

 reflection profiling techniques. 



