In situ measurements of compressional and shear wave propagation in marine sediments and comparison to geoacoustic models

2018 ◽  
Vol 144 (3) ◽  
pp. 1960-1960
Author(s):  
Kevin M. Lee ◽  
Megan S. Ballard ◽  
Andrew R. McNeese ◽  
Gabriel R. Venegas ◽  
Preston S. Wilson
Keyword(s):  
Wave Propagation ◽  
Shear Wave ◽  
Marine Sediments ◽  
In Situ Measurements

scholarly journals Assessing the Power of Intensity Interaction between the Solid and Fluid Phases in the Unconsolidated Water-Saturated Sandy Marine Sediments at Shear Wave Propagation

2021 ◽  
Vol 37 (1) ◽  
Author(s):  
V. A. Lisyutin ◽  
O. R. Lastovenko ◽  
◽  
Keyword(s):  
Wave Propagation ◽  
Shear Wave ◽  
Attenuation Coefficient ◽  
Marine Sediments ◽  
Pore Space ◽  
Equation Of Motion ◽  
Relative Movement ◽  
Two Phase ◽  
Dissipative Effects ◽  
Sandy Sediments

Purpose. Propagation of a shear wave in sandy marine sediments is considered. The acoustic properties of a shear wave are the phase velocity and the attenuation coefficient. It is known that in dry sandy sediments, the attenuation coefficient is directly proportional to frequency. In the saturated mediums, there are the deviations from this law that implies existence of two physical mechanisms of losses – the intergranular friction and viscous loss. The study is aimed at developing a two-phase theoretical model of the shear wave propagation in the unconsolidated marine sediments, and at identifying the dissipative effects caused by the fluid relative movement in the pore space. Methods and Results. The intergranular friction is modeled using a springpot, which represents an element combing conservative properties of a spring and dissipative ones of a dashpot. The equation of motion is applied, where a part of fluid is assumed to be associated with the media solid phase and another part is considered to be mobile. For a harmonic displacement, the equations of state and the equation of motion yield a new two-phase dispersion relation (the theory of Grain Shearing + + Effective Density, or GS + EDs, for short). The results of the GS + EDs theory are compared with the data of the velocity and attenuation measurements taken from the open sources. It is shown that during propagation of the compressional and shear waves, the mechanisms of interaction between the granules, and between the granules and fluid are not similar. Character of the changes in the grain-tograin friction parameters when the pore space is saturated with fluid, is analyzed. Conclusion. Manifestation of the dissipative effects resulting from the pore saturation with fluid depends on the density of the granules packing. In case of a dense packing, there are no conditions for the fluid relative movement, and the sandy sediments exhibit the property of a constant Q-factor. If the packing is loose, the viscous losses make a significant contribution, and the attenuation frequency dependence is nonlinear. The effective pore sizes for the compression and shear waves do not coincide.

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

Geophysics ◽  
1976 ◽  
Vol 41 (5) ◽  
pp. 985-996 ◽  
Author(s):  
Edwin L. Hamilton
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Marine Sediments ◽  
Shear Wave Velocity ◽  
Shear Waves ◽  
Shear Velocity ◽  
Velocity Versus ◽  
Velocity Data ◽  
Velocity Gradients

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.

Simulation of downhole and crosshole seismic tests on sand using the hydraulic gradient similitude method

1990 ◽  
Vol 27 (4) ◽  
pp. 441-460 ◽  
Author(s):  
Li Yan ◽  
Peter M. Byrne
Keyword(s):  
Wave Propagation ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Stress Ratio ◽  
Velocity Ratio ◽  
Hydraulic Gradient ◽  
Empirical Equations ◽  
Wave Measurement

A method of simulating downhole and crosshole seismic shear-wave tests in a model under controlled stress conditionsis described. The downhole and shear wave in horizontal plane (SH) crosshole shear waves are generated and received along the principal stress axes using piezoceramic bender elements. The K0in situ stress conditions, including loading and unloading stress paths, are simulated by the hydraulic gradient similitude method, which allows high stresses simulating field conditions to be obtained. The horizontal stress during the tests is directly measured by a lateral total-stress transducer. The test data are used to evaluate various published empirical equations that relate shear-wave velocity and soil stress state. It is found that although the various empirical equations can predict the in situ shear-wave velocity profile reasonably well, only the equation that relates the shear-wave velocity to the individual principal stresses in the directions of wave propagation and particle motion can predict the variation of the velocity ratio between the downhole and SH crosshole tests. It was also found that the stress ratio has some effects on the downhole (or shear wave in vertical plane (SV) crosshole) shear-wave velocity, but not on the SH crosshole shear-wave velocity. This indicates that it is only the stress ratio in the plane of wave propagation that is important to the shear-wave velocity. Comparison between the downhole and SH crosshole shows that structure anisotropy is in the order of 10%. In addjtion, K0 values are predicted from shear-wave measurement and compared with measured ones. The difficulties in obtaining K0 values from shear-wave measurement are also discussed. Key words: hydraulic gradient, model tests, downhole and crosshole shear-wave tests, sand.

In situ measurements of sediment compressional and shear wave properties in Currituck Sound

2015 ◽  
Vol 137 (4) ◽  
pp. 2282-2282 ◽  
Author(s):  
Megan S. Ballard ◽  
Kevin M. Lee ◽  
Andrew R. McNeese ◽  
Preston S. Wilson ◽  
Thomas G. Muir ◽  
...  
Keyword(s):  
Shear Wave ◽  
In Situ Measurements ◽  
Currituck Sound ◽  
Wave Properties

scholarly journals Assessing the Power of Intensity Interaction between the Solid and Fluid Phases in the Unconsolidated Water-Saturated Sandy Marine Sediments at Shear Wave Propagation

2021 ◽  
Vol 28 (1) ◽  
Author(s):  
V. A. Lisyutin ◽  
O. R. Lastovenko ◽  
◽  
Keyword(s):  
Wave Propagation ◽  
Shear Wave ◽  
Attenuation Coefficient ◽  
Marine Sediments ◽  
Pore Space ◽  
Equation Of Motion ◽  
Relative Movement ◽  
Two Phase ◽  
Dissipative Effects ◽  
Sandy Sediments

Purpose. Propagation of a shear wave in sandy marine sediments is considered. The acoustic properties of a shear wave are the phase velocity and the attenuation coefficient. It is known that in dry sandy sediments, the attenuation coefficient is directly proportional to frequency. In the saturated mediums, there are the deviations from this law that implies existence of two physical mechanisms of losses – the intergranular friction and viscous loss. The study is aimed at developing a two-phase theoretical model of the shear wave propagation in the unconsolidated marine sediments, and at identifying the dissipative effects caused by the fluid relative movement in the pore space. Methods and Results. The intergranular friction is modeled using a springpot, which represents an element combing conservative properties of a spring and dissipative ones of a dashpot. The equation of motion is applied, where a part of fluid is assumed to be associated with the media solid phase and another part is considered to be mobile. For a harmonic displacement, the equations of state and the equation of motion yield a new two-phase dispersion relation (the theory of Grain Shearing + Effective Density, or GS + EDs, for short). The results of the GS + EDs theory are compared with the data of the velocity and attenuation measurements taken from the open sources. It is shown that during propagation of the compressional and shear waves, the mechanisms of interaction between the granules, and between the granules and fluid are not similar. Character of the changes in the grain-to-grain friction parameters when the pore space is saturated with fluid, is analyzed. Conclusions. Manifestation of the dissipative effects resulting from the pore saturation with fluid depends on the density of the granules packing. In case of a dense packing, there are no conditions for the fluid relative movement, and the sandy sediments exhibit the property of constant Q-factor. If the packing is loose, the viscous losses make a significant contribution, and the attenuation frequency dependence is nonlinear. The effective pore sizes for the compression and shear waves do not coincide.

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