OBSERVATIONS ON ATTENUATION AND SHEAR-WAVE VELOCITY IN FINE-GRAINED, MARINE-SEDIMENTS

Compressional(P)-wave attenuation, shear(S)-wave attenuation, and shea r(S)-wave velocity measurements, compiled for fine-grained, unconsolid ated sediments, show trends that do not support empirical relationship s [Hamilton, J. Acoust. Soc. Am. 68, 1313-1340 (1980); in Acoustics an d Ocean Bottom (F. A. S. E. Specialize Conf., Madrid, 1987)] commonly used for geoacoustic modeling. The exception is compressional-wave att enuation data, from 10 Hz to 500 kHz, that essentially follow a freque ncy dependence of f(1) (+/-2 standard deviations). P-wave attenuation with depth is difficult, if not impossible, to predict given the varia bility in the data. Examination of several attenuation/depth profiles indicates that those of Mitchell and Focke [J. Acoust. Sec. Am. 67, 15 82-1589 (1980)] may be the best choice for predicting P-wave attenuati on with depth at the present time. The assumption that S-wave and F-wa ve attenuations are proportional [Hamilton, J. Acoust. Sec. Am. 60, 33 4-338 (1976c); in Acoustics and Ocean Bottom (F. A. S. E. Specialize C onf., Madrid, 1987)] is not supported by the data. S-wave attenuations calculated from effective stress mimmick the data, however, suggestin g this as a better method for predicting S-wave attenuation with depth . S-wave velocity/depth profiles fall into high- and low-velocity grou ps that (1) reflect gross differences in sediment texture, and (2) dem onstrate the importance of sediment characterization in order to selec t an appropriate velocity/depth function.