SHEAR‐WAVE VELOCITY VERSUS DEPTH IN MARINE SEDIMENTS: A REVIEW

Abstract

The objectives of this paper are to review and study selected measurements of the velocity of shear waves at various depths in some principal types of unlithified, water‐saturated sediments, and to discuss probable variations of shear velocity as a function of pressure and depth in the sea floor. Because of the lack of data for the full range of marine sediments, data from measurements on land were used, and the study was confined to the two “end‐member” sediment types (sand and silt‐clays) and turbidites. The shear velocity data in sands included 29 selected in‐situ measurements at depths to 12 m. The regression equation for these data is: [Formula: see text], where [Formula: see text] is shear‐wave velocity in m/sec, and D is depth in meters. The data from field and laboratory studies indicate that shear‐wave velocity is proportional to the 1/3 to 1/6 power of pressure or depth in sands; that the 1/6 power is not reached until very high pressures are applied; and that in most sand bodies the velocity of shear waves is proportional to the 3/10 to 1/4 power of depth or pressure. The use of a depth exponent of 0.25 is recommended for prediction of shear velocity versus depth in sands. The shear velocity data in silt‐clays and turbidites include 47 selected in‐situ measurements at depths to 650 m. Three linear equations are used to characterize the data. The equation for the 0 to 40 m interval [Formula: see text] indicates the gradient [Formula: see text] to be 4 to 5 times greater than is the compressional velocity gradient in this interval in comparable sediments. At deeper depths, shear velocity gradients are [Formula: see text] from 40 to 120 m, and [Formula: see text] from 120 to 650 m. These deeper gradients are comparable to those of compressional wave velocities. These shear velocity gradients can be used as a basis for predicting shear velocity versus depth.