Converted waves in a shallow marine environment: Experimental and modeling studies

Geophysics ◽  
2011 ◽  
Vol 76 (1) ◽  
pp. T1-T11 ◽  
Author(s):  
Nihed Allouche ◽  
Guy G. Drijkoningen ◽  
Willem Versteeg ◽  
Ranajit Ghose
Keyword(s):  
Shallow Water ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Shear Waves ◽  
Seismic Survey ◽  
Wave Source ◽  
Shallow Marine ◽  
Modeling Studies ◽  
Water Bottom

Seismic waves converted from compressional to shear mode in the shallow subsurface can be useful not only for obtaining shear-wave velocity information but also for improved processing of deeper reflection data. These waves generated at deep seas have been used successfully in hydrocarbon exploration; however, acquisition of good-quality converted-wave data in shallow marine environments remains challenging. We have looked into this problem through field experiments and synthetic modeling. A high-resolution seismic survey was conducted in a shallow-water canal using different types of seismic sources; data were recorded with a four-component water-bottom cable. Observed events in the field data were validated through modeling studies. Compressional waves converted to shear waves at the water bot-tom and at shallow reflectors were identified. The shear waves showed distinct linear polarization in the horizontal plane and low velocities in the marine sediments. Modeling results indicated the presence of a nongeometric shear-wave arrival excited only when the dominant wavelength exceeded the height of the source with respect to the water/sediment interface, as observed in air-gun data. This type of shear wave has a traveltime that corresponds to the raypath originating not at the source but at the interface directly below the source. Thus, these shear waves, excited by the source/water-bottom coupled system, kinematically behave as if they were generated by an S-wave source placed at the water bottom. In a shallow-water environment, the condition appears to be favorable for exciting such shear waves with nongeometric arrivals. These waves can provide useful information of shear-wave velocity in the sediments.

Effect of Anisotropy on Shear Wave Velocity in Wood

2012 ◽  
Vol 535-537 ◽  
pp. 1923-1926
Author(s):  
Jian Ping Zhou ◽  
Jin Xia Liu ◽  
Wen Yang Gao ◽  
Zhi Wen Cui ◽  
Wei Guo Lv ◽  
...  
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Radial Direction ◽  
Rotation Angle ◽  
Wood Specimen ◽  
Shear Waves ◽  
Circular Ring ◽  
The Relationship ◽  
Intrinsic Birefringence

The velocities of shear waves propagating along radial direction of birch and elmwood specimens are measured in order to study the effect of anisotropy on shear wave velocity. The relationship between the shear wave velocity and the oscillation direction is examined by rotating an ultrasonic sensor. The results indicate that the effect of anisotropy on shear wave velocity in birch and elmwood specimens is similar to Japanese magnolia specimen. When the oscillation direction of the shear wave corresponds to the certain anisotropic direction of the wood specimen, the shear wave velocity decreases sharply and the relationship between shear wave velocity and rotation angle tends to become discontinuous. The intrinsic birefringence due to the anisotropy of birch and elmwood woods is observed. Their texture anisotropies are strong. In an isotropic nylon, on the contrary, the value of shear wave velocity was similar to a circular ring. This investigation is significant meanings in architectural and civil engineering field.

Characterization of Clay Sedimentation Using Piezoelectric Bender Elements

2006 ◽  
Vol 321-323 ◽  
pp. 1415-1420 ◽  
Author(s):  
Il Han Chang ◽  
Gye Chun Cho ◽  
Joo Gong Lee ◽  
Lee Hyung Kim
Keyword(s):  
Structure Formation ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Soil Structure ◽  
Abrupt Change ◽  
Shear Waves ◽  
Measurement Techniques ◽  
The Self ◽  
Bender Elements

Sedimentation is one of the most basic processes in the formation of a soil structure in nature. Many studies have been performed to describe the characteristics of clay sedimentation, based on settlement and water content measurement. In addition, there have been some attempts in numerical modeling to describe soil structure formation as a whole. However, these effects still fall short in explaining the overall process of soil structure formation because some relevant properties are measured after a self-weight consolidation is completed. Furthermore some measurement techniques significantly alter soil structure. Thus, a non-destructive evaluation is necessary for the effective description of soil characteristics during the sedimentation process. In this study, a testing device is designed that continuously monitors the self-weight consolidation process of sedimentation with shear waves. Piezoelectric bender elements are installed into a testing cell to generate and receive shear waves in a small strain regime. Slurries are prepared with kaolinite-type clay and placed in the cell. Shear wave velocities are continuously measured as a function of time during the whole process of the self weight consolidation. The experimental results suggest that as clay sediment is subjected to a certain loading, the shear wave velocity increases as time increases, showing an abrupt change in log time. This abrupt change is relevant to the formation of a stable soil skeleton. It is concluded that the time-dependent variations in shear wave velocity reflect sedimentation and self weight consolidation behavior and the evolution of the effective stress increment.

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.

scholarly journals Characterization of Shear Waves in Busan New Port Clay: Estimation of the Coefficients of Shear Wave Velocity

2013 ◽  
Vol 23 (4) ◽  
pp. 503-510
Author(s):  
Jong-Sub Lee ◽  
Youngseok Kim ◽  
Seungseo Hong ◽  
Hyung-Koo Yoon
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Shear Waves

Physics of shear-waves propagating in saturated and unsaturated soils: new potential for monitoring soil dynamics and stability

2021 ◽  
Author(s):  
Ranajit Ghose
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Unsaturated Soils ◽  
Shear Waves ◽  
Soil Layer ◽  
Time Lapse ◽  
Soil Dynamics ◽  
Near Surface

<p>Shear waves are uniquely informative because of their vector nature – with both polarization and propagation of shear waves being useful sources of information, their sensitivity to <em>in-situ</em> stress and grain-to-grain contact, and also because of the low velocity of shear waves in relatively soft formations - offering short wavelength and hence high resolution. Decimetre-scale resolution found in shear-wave reflection data in soft soil has resulted in new application possibilities. Medium anisotropy extracted from multi-component shear-wave data has provided information on natural symmetries in small-strain rigidity and/or stress in the shallow subsurface, which are caused by factors that are of great interest to the engineers. AVO response of shear waves at near-surface soil-layer boundaries has also proven to be useful for extracting local information in the subsoil.</p><p>In the present research we have looked at the sensitivity of shear-wave velocity and the underlying physics in both saturated and unsaturated near-surface soils, and if these can practically be used for monitoring soil dynamics and soil stability. Time-lapse changes in shear-wave velocity could be used to monitor changes in <em>in-situ</em> stress in the saturated sands. More recently, we have developed methodologies to invert time-lapse shear-wave velocity information together with geo-electrical information to obtain<em> in-situ</em> values of water saturation and suction in different partially saturated soil units. Incorporation of this information in a spatially varying sense is imperative in order to make assessment of stability of unsaturated soil slopes subjected to rainfall, modelling flooding and sediment flows due to increased surface runoff and erosion, sustainable agriculture through in-situ water moisture monitoring, and modelling pollutant transport through soils.</p>

scholarly journals Piezoelectric Ring Bender for Characterization of Shear Waves in Compacted Sandy Soils

Sensors ◽  
2021 ◽  
Vol 21 (4) ◽  
pp. 1226
Author(s):  
Dong-Ju Kim ◽  
Jung-Doung Yu ◽  
Yong-Hoon Byun
Keyword(s):  
Shear Modulus ◽  
Water Content ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Shear Waves ◽  
Small Strain ◽  
The Other ◽  
Compacted Soils ◽  
Small Strain Shear Modulus

Shear wave velocity and small-strain shear modulus are widely used as the mechanical properties of soil. The objective of this study is to develop a new shear wave monitoring system using a pair of piezoelectric ring benders (RBs) and to evaluate the suitability of RB in compacted soils compared with the bender element and ultrasonic transducer. The RB is a multilayered piezoelectric actuator, which can generate shear waves without disturbing soils. For five compacted soil specimens, the shear waves are monitored by using three different piezoelectric transducers. Results of time-domain response show that the output signals measured from the RB vary according to the water content of the specimen and the frequency of the input signal. Except at the water content of 9.3%, the difference in the resonant frequencies between the three transducers is not significant. The shear wave velocities for the RB are slightly greater than those for the other transducers. For the RB, the exponential relationship between the shear wave velocity and dry unit weight is better established compared with that of the other transducers. The newly proposed piezoelectric transducer RB may be useful for the evaluation of the shear wave velocity and small-strain shear modulus of compacted soils.

Nongeometrically converted shear waves in marine streamer data

Geophysics ◽  
2012 ◽  
Vol 77 (6) ◽  
pp. P45-P56 ◽  
Author(s):  
Guy Drijkoningen ◽  
Nihed el Allouche ◽  
Jan Thorbecke ◽  
Gábor Bada
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Body Wave ◽  
Shear Waves ◽  
Compressional Wave ◽  
Body Waves ◽  
P Wave ◽  
Streamer Data ◽  
Propagating Shear ◽  
Water Bottom

Under certain circumstances, marine streamer data contain nongeometrical shear body wave arrivals that can be used for imaging. These shear waves are generated via an evanescent compressional wave in the water and convert to propagating shear waves at the water bottom. They are called “nongeometrical” because the evanescent part in the water does not satisfy Snell’s law for real angles, but only for complex angles. The propagating shear waves then undergo reflection and refraction in the subsurface, and arrive at the receivers via an evanescent compressional wave. The required circumstances are that sources and receivers are near the water bottom, irrespective of the total water depth, and that the shear-wave velocity of the water bottom is smaller than the P-wave velocity in the water, most often the normal situation. This claim has been tested during a seismic experiment in the river Danube, south of Budapest, Hungary. To show that the shear-related arrivals are body rather than surface waves, a borehole was drilled and used for multicomponent recordings. The streamer data indeed show evidence of shear waves propagating as body waves, and the borehole data confirm that these arrivals are refracted shear waves. To illustrate the effect, finite-difference modeling has been performed and it confirmed the presence of such shear waves. The streamer data were subsequently processed to obtain a shear-wave refraction section; this was obtained by removing the Scholte wave arrival, separating the wavefield into different refracted arrivals, stacking and depth-converting each refracted arrival before adding the different depth sections together. The obtained section can be compared directly with the standard P-wave reflection section. The comparison shows that this approach can deliver refracted-shear-wave sections from streamer data in an efficient manner, because neither the source nor receivers need to be situated on the water bottom.

Estimation of shear wave velocity in shallow marine sediments

1994 ◽  
Vol 19 (1) ◽  
pp. 58-72 ◽  
Author(s):  
A. Caiti ◽  
T. Akal ◽  
R.D. Stoll
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Marine Sediments ◽  
Shear Wave Velocity ◽  
Shallow Marine ◽  
Shallow Marine Sediments

scholarly journals P1538 Light exercise may induce an increase in the propagation velocity of naturally occurring shear waves

2020 ◽  
Vol 21 (Supplement_1) ◽  
Author(s):  
M Strachinaru ◽  
L B H Keijzer ◽  
D J Bowen ◽  
M L Geleijnse ◽  
A F W Van Der Steen ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Propagation Velocity ◽  
Shear Waves ◽  
Significant Rise ◽  
Valve Closure ◽  
Naturally Occurring

Abstract Background Shear waves (SW) are induced in the myocardium by the closure of the valves. Recent studies show variations in their propagation velocity with age, gender or pathology. However, these valve-induced waves occur during relaxation and contraction. This means that the instantaneous SW velocity, as measure for stiffness, might not only depend on the intrinsic elastic properties of the relaxed myocardium, but also on its contractility and the exact moment of valve closure. The latter can change with heart rate and loading conditions, which could induce variance in measurement. Purpose This study aimed to investigate the effect of light exercise on the propagation velocity of naturally occurring shear waves. Methods Ten healthy volunteers underwent high frame rate (over 500 Hz) color TDI studies at rest and during light physiological stress (handgrip exercise). Shear wave velocities were averaged over several heart beats. Values obtained were compared by using the Wilcoxon signed ranks test and a Bland-Altman analysis. Results The light physiological exercise test induced a small but statistically significant rise in diastolic blood pressure and heart rate (table). The shear wave velocity after aortic valve closure (ASW) could be quantified in each subject at rest and during stress. The shear wave tracking after mitral valve closure (MSW) was only feasible for 8 subjects at rest and 6 during stress. There was an average difference of 0.4 ± 0.3 m/s (LOA= -0.18 to 0.97 m/s) between stress and rest measurements for the ASW velocity, which was statistically significant(p = 0.01, Figure). For the MSW the average difference was 0.02 ± 0.5 m/s (LOA= -1.02 to 1.06 m/s), p = 0.9. Conclusion We observed a statistically significant rise in the shear wave velocity after aortic valve closure but not after mitral closure during a light exercise. Although the statistical power of this study is relatively small, the results may suggest that naturally occurring shear waves velocity can be influenced by heart rate and loading conditions. Table Parameter Rest Stress P Age [yr] 30 ± 6 - - BMI [kg/m2] 22 ± 2 - - Heartrate [bpm] 62 ± 7 67 ± 8 <0.01 Systolic blood pressure [mmHg] 106 ± 13 110 ± 10 0.08 Diastolic blood pressure [mmHg] 62 ± 9 67 ± 9 0.01 Aortic shear wave velocity [m/s] 3.26 ± 0.4 3.65 ± 0.7 0.01 Mitral shear wave velocity [m/s] 4.56 ± 0.7 4.83 ± 0.8 0.9 Abstract P1538 Figure

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