A new method for estimating shear-wave velocity in marine sediments from radiation impedance measurements

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.

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1.5D inversion of lateral variation of Scholte‐wave dispersion

Geophysics ◽

10.1190/1.1707052 ◽

2004 ◽

Vol 69 (2) ◽

pp. 330-344 ◽

Cited By ~ 69

Author(s):

Thomas Bohlen ◽

Simone Kugler ◽

Gerald Klein ◽

Friedrich Theilen

Keyword(s):

Shear Wave ◽

Wave Velocity ◽

Marine Sediments ◽

Shear Wave Velocity ◽

Wave Dispersion ◽

Lateral Variation ◽

Sea Floor ◽

Air Gun ◽

Scholte Wave ◽

The Common

Reliable models of in‐situ shear‐wave velocities of shallow‐water marine sediments are important for geotechnical applications, lithological sediment characterization, and seismic exploration studies. We infer the 2D shear‐wave velocity structure of shallow‐water marine sediments from the lateral variation of Scholte‐wave dispersion. Scholte waves are recorded in a common receiver gather generated by an air gun towed behind a ship away from a single stationary ocean‐bottom seismometer. An offset window moves along the common receiver gather to pick up a local wavefield. A slant stack produces a slowness–frequency spectrum of the local wavefield, which contains all modes excited by the air gun. Amplitude maxima (dispersion curves) in the local spectrum are picked and inverted for the shear‐wave velocity depth profile located at the center of the window. As the window continuously moves along the common receiver gather, a 2D shear‐wave velocity section is generated. In a synthetic example the smooth lateral variation of surficial shear‐wave velocity is well reconstructed. The method is applied to two orthogonal common receiver gathers acquired in the Baltic Sea (northern Germany). The inverted 2D models show a strong vertical gradient of shear‐wave velocity at the sea floor. Along one profile significant lateral variation near the sea floor is observed.

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Shear wave velocity measurements in marine sediments

Geo-Marine Letters ◽

10.1007/bf02462766 ◽

1982 ◽

Vol 2 (3-4) ◽

pp. 215-217 ◽

Cited By ~ 4

Author(s):

J. E. Matthews

Keyword(s):

Shear Wave ◽

Wave Velocity ◽

Marine Sediments ◽

Shear Wave Velocity ◽

Velocity Measurements

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