Estimation of static corrections for shear‐wave profiling using the dispersion properties of Love waves

Geophysics ◽  
1984 ◽  
Vol 49 (8) ◽  
pp. 1169-1179 ◽  
Author(s):  
J. L. Mari
Keyword(s):  
Phase Velocity ◽  
Shear Wave ◽  
Noise Analysis ◽  
Wave Dispersion ◽  
Group Extension ◽  
Love Waves ◽  
Dispersion Property ◽  
P Waves ◽  
Weathered Zone ◽  
Static Corrections

When processing shear‐wave data it is often difficult to compute the static corrections using the same methods as for P-waves, because of the low velocities involved and of the interference with residual P-waves. A method especially tailored for static corrections of SH-waves is presented, which makes use of the dispersion property of Love waves. Assuming that the weathered zone of thickness H acts as a wave guide for the surface waves, their phase velocity ranges from [Formula: see text] at infinite frequency to [Formula: see text] at zero frequency, where [Formula: see text] and [Formula: see text] are the shear‐wave velocities into and below the weathered zone. For intermediate frequencies the phase velocity of Love waves is a known function of H, [Formula: see text] and [Formula: see text]. If the phase velocity of Love waves is measured on field records for a number of distinct frequencies, it is therefore possible to compute H, [Formula: see text], [Formula: see text], and the static corrections. In contrast with conventional techniques which require first arrivals to be picked manually, the computation of static corrections using the dispersion of Love waves is essentially based on velocity analysis efficiently performed by digital computers. Three field examples were conducted. The first of these was a noise analysis using 256 geophone positions ranging from 3 to 258 m. The two other examples are CDP lines obtained with polarized SH sources. The geophone group extension is 20 m and the distance between groups is 10 m. In all these examples, the upper layer thickness and velocity values resulting from the Love wave dispersion appeared to be in good agreement with those computed from the conventional methods.

scholarly journals Scholte Wave Dispersion Modeling and Subsequent Application in Seabed Shear-Wave Velocity Profile Inversion

2021 ◽  
Vol 9 (8) ◽  
pp. 840
Author(s):  
Yang Dong ◽  
Shengchun Piao ◽  
Lijia Gong ◽  
Guangxue Zheng ◽  
Kashif Iqbal ◽  
...  
Keyword(s):  
Velocity Profile ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Wave Dispersion ◽  
Dispersion Property ◽  
Scholte Wave ◽  
Shear Wave Velocity Profile ◽  
Masw Method ◽  
Low Shear

Recent studies have illustrated that the Multichannel Analysis of Surface Waves (MASW) method is an effective geoacoustic parameter inversion tool. This particular tool employs the dispersion property of broadband Scholte-type surface wave signals, which propagate along the interface between the sea water and seafloor. It is of critical importance to establish the theoretical Scholte wave dispersion curve computation model. In this typical study, the stiffness matrix method is introduced to compute the phase speed of the Scholte wave in a layered ocean environment with an elastic bottom. By computing the phase velocity in environments with a typical complexly varying seabed, it is observed that the coupling phenomenon occurs among Scholte waves corresponding to the fundamental mode and the first higher-order mode for the model with a low shear-velocity layer. Afterwards, few differences are highlighted, which should be taken into consideration while applying the MASW method in the seabed. Finally, based on the ingeniously developed nonlinear Bayesian inversion theory, the seafloor shear wave velocity profile in the southern Yellow Sea of China is inverted by employing multi-order Scholte wave dispersion curves. These inversion results illustrate that the shear wave speed is below 700 m/s in the upper layers of bottom sediments. Due to the alternation of argillaceous layers and sandy layers in the experimental area, there are several low-shear-wave-velocity layers in the inversion profile.

A crust and upper mantle model for Novaya Zemlya from Rayleigh-wave dispersion data

1978 ◽  
Vol 68 (6) ◽  
pp. 1651-1662
Author(s):  
Douglas W. McCowan ◽  
Peter Glover ◽  
Shelton S. Alexander
Keyword(s):  
Phase Velocity ◽  
Rayleigh Wave ◽  
Shear Wave ◽  
Upper Mantle ◽  
Wave Dispersion ◽  
Surface Wave Dispersion ◽  
Crust And Upper Mantle ◽  
Novaya Zemlya ◽  
Phase Velocity Dispersion ◽  
Single Station

abstract We derive a shear-wave crust and upper mantle structure for the southern part of Novaya Zemlya by an application of the two-event, single-station method of Rayleigh-wave phase-velocity dispersion analysis. This method provides a means of isolating the surface-wave dispersion characteristics of a remote source region using only teleseismic recordings. The observed phase-velocity data are then systematically inverted to obtain a best-fitting model. Our preferred model has a 45-km thick crust with no shear-wave low-velocity zone in the upper mantle. It is similar to published structures for the southern Ural mountains and is therefore compatible with the premise that Novaya Zemlya is a nothern extension of the Urals.

scholarly journals Shear Wave Dispersion as a Potential Biomarker for Cervical Remodeling During Pregnancy: Evidence From a Non-Human Primate Model

2021 ◽  
Vol 8 ◽  
Author(s):  
Abel Torres ◽  
Mark L. Palmeri ◽  
Helen Feltovich ◽  
Timothy J. Hall ◽  
Ivan M. Rosado-Mendez
Keyword(s):  
Singular Value Decomposition ◽  
Phase Velocity ◽  
Shear Wave ◽  
Maternal Age ◽  
Late Pregnancy ◽  
Wave Dispersion ◽  
Singular Value ◽  
Automatic Frequency ◽  
Cervical Remodeling ◽  
Value Decomposition

Shear wave dispersion (variation of phase velocity with frequency) occurs in tissues with layered and anisotropic microstructure and viscous components, such as the uterine cervix. This phenomenon, mostly overlooked in previous applications of cervical Shear Wave Elasticity Imaging (SWEI) for preterm birth risk assessment, is expected to change drastically during pregnancy due to cervical remodeling. Here we demonstrate the potential of SWEI-based descriptors of dispersion as potential biomarkers for cervical remodeling during pregnancy. First, we performed a simulation-based pre-selection of two SWEI-based dispersion descriptors: the ratio R of group velocities computed with particle-velocity and particle-displacement, and the slope S of the phase velocity vs. frequency. The pre-selection consisted of comparing the contrast-to-noise ratio (CNR) of dispersion descriptors in materials with different degrees of dispersion with respect to a low-dispersive medium. Shear waves induced in these media by SWEI were simulated with a finite-element model of Zener viscoelastic solids. The pre-selection also considered two denoising strategies to improve CNR: a low-pass filter with automatic frequency cutoff determination, and singular value decomposition of shear wave displacements. After pre-selection, the descriptor-denoising combination that produced the largest CNR was applied to SWEI cervix data from 18 pregnant Rhesus macaques acquired at weeks 10 (mid-pregnancy stage) and 23 (late pregnancy stage) of the 24.5-weeks full pregnancy. A maximum likelihood linear mixed-effects model (LME) was used to evaluate the dependence of the dispersion descriptor on pregnancy stage, maternal age, parity and other experimental factors. The pre-selection study showed that descriptor S combined with singular value decomposition produced a CNR 11.6 times larger than the other descriptor and denoising strategy combinations. In the Non-Human Primates (NHP) study, the LME model showed that descriptor S significantly decreased from mid to late pregnancy (−0.37 ± 0.07 m/s-kHz per week, p< 0.00001) with respect to the base value of 15.5 ± 1.9 m/s-kHz. This change was more significant than changes in other SWEI features such as the group velocity previously reported. Also, S varied significantly between the anterior and posterior portions of the cervix (p= 0.02) and with maternal age (p= 0.008). Given the potential of shear wave dispersion to track cervical remodeling, we will extend its application to ongoing longitudinal human studies.

An initial study of complete 2D shear wave dispersion images using a reverberant shear wave field

2019 ◽  
Vol 64 (14) ◽  
pp. 145009 ◽  
Author(s):  
Juvenal Ormachea ◽  
Kevin J Parker ◽  
Richard G Barr
Keyword(s):  
Wave Field ◽  
Shear Wave ◽  
Wave Dispersion ◽  
Initial Study

Finite-Difference Modeling and Characteristics Analysis of Love Waves in Anisotropic-Viscoelastic Media

2021 ◽  
Author(s):  
Shichuan Yuan ◽  
Zhenguo Zhang ◽  
Hengxin Ren ◽  
Wei Zhang ◽  
Xianhai Song ◽  
...  
Keyword(s):  
Finite Difference ◽  
Phase Velocity ◽  
Velocity Dispersion ◽  
Love Waves ◽  
Velocity Anisotropy ◽  
Viscoelastic Media ◽  
Phase Velocities ◽  
Phase Velocity Dispersion ◽  
Anisotropic Elastic ◽  
Attenuation Anisotropy

ABSTRACT In this study, the characteristics of Love waves in viscoelastic vertical transversely isotropic layered media are investigated by finite-difference numerical modeling. The accuracy of the modeling scheme is tested against the theoretical seismograms of isotropic-elastic and isotropic-viscoelastic media. The correctness of the modeling results is verified by the theoretical phase-velocity dispersion curves of Love waves in isotropic or anisotropic elastic or viscoelastic media. In two-layer half-space models, the effects of velocity anisotropy, viscoelasticity, and attenuation anisotropy of media on Love waves are studied in detail by comparing the modeling results obtained for anisotropic-elastic, isotropic-viscoelastic, and anisotropic-viscoelastic media with those obtained for isotropic-elastic media. Then, Love waves in three typical four-layer half-space models are simulated to further analyze the characteristics of Love waves in anisotropic-viscoelastic layered media. The results show that Love waves propagating in anisotropic-viscoelastic media are affected by both the anisotropy and viscoelasticity of media. The velocity anisotropy of media causes substantial changes in the values and distribution range of phase velocities of Love waves. The viscoelasticity of media leads to the amplitude attenuation and phase velocity dispersion of Love waves, and these effects increase with decreasing quality factors. The attenuation anisotropy of media indicates that the viscoelasticity degree of media is direction dependent. Comparisons of phase velocity ratios suggest that the change degree of Love-wave phase velocities due to viscoelasticity is much less than that caused by velocity anisotropy.

STATIC CORRECTIONS FOR SHEAR WAVE SECTIONS*

1984 ◽  
Vol 32 (6) ◽  
pp. 1091-1102 ◽  
Author(s):  
B. WIEST ◽  
H. A. K. EDELMANN
Keyword(s):  
Shear Wave ◽  
Static Corrections

scholarly journals Sensitivities of surface wave velocities to the medium parameters in a radially anisotropic spherical Earth and inversion strategies

2015 ◽  
Vol 58 (5) ◽  
Author(s):  
Sankar N. Bhattacharya
Keyword(s):  
Surface Wave ◽  
Phase Velocity ◽  
Group Velocity ◽  
Wave Velocity ◽  
Love Waves ◽  
P Wave ◽  
Model Parameters ◽  
Nonlinear Inversion ◽  
Wave Velocities ◽  
Spherical Earth

<p>Sensitivity kernels or partial derivatives of phase velocity (<em>c</em>) and group velocity (<em>U</em>) with respect to medium parameters are useful to interpret a given set of observed surface wave velocity data. In addition to phase velocities, group velocities are also being observed to find the radial anisotropy of the crust and mantle. However, sensitivities of group velocity for a radially anisotropic Earth have rarely been studied. Here we show sensitivities of group velocity along with those of phase velocity to the medium parameters <em>V<sub>SV</sub>, V<sub>SH </sub>, V<sub>PV</sub>, V<sub>PH , </sub></em><em>h</em><em> </em>and density in a radially anisotropic spherical Earth. The peak sensitivities for <em>U</em> are generally twice of those for <em>c</em>; thus <em>U</em> is more efficient than <em>c</em> to explore anisotropic nature of the medium. Love waves mainly depends on <em>V<sub>SH</sub></em> while Rayleigh waves is nearly independent of <em>V<sub>SH</sub></em> . The sensitivities show that there are trade-offs among these parameters during inversion and there is a need to reduce the number of parameters to be evaluated independently. It is suggested to use a nonlinear inversion jointly for Rayleigh and Love waves; in such a nonlinear inversion best solutions are obtained among the model parameters within prescribed limits for each parameter. We first choose <em>V<sub>SH</sub></em>, <em>V<sub>SV </sub></em>and <em>V<sub>PH</sub></em> within their corresponding limits; <em>V<sub>PV</sub></em> and <em>h</em> can be evaluated from empirical relations among the parameters. The density has small effect on surface wave velocities and it can be considered from other studies or from empirical relation of density to average P-wave velocity.</p>

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