GSpecDisp: A matlab GUI package for phase-velocity dispersion measurements from ambient-noise correlations

2018 ◽  
Vol 110 ◽  
pp. 41-53 ◽  
Author(s):  
Hamzeh Sadeghisorkhani ◽  
Ólafur Gudmundsson ◽  
Ari Tryggvason
Keyword(s):  
Phase Velocity ◽  
Ambient Noise ◽  
Velocity Dispersion ◽  
Phase Velocity Dispersion

Shear-wave structure of southern Sweden from precise phase-velocity measurements of ambient-noise data

2020 ◽  
Author(s):  
Hamzeh Sadeghisorkhani ◽  
Ólafur Gudmundsson ◽  
Ka Lok Li ◽  
Ari Tryggvason ◽  
Björn Lund ◽  
...  
Keyword(s):  
Phase Velocity ◽  
Ambient Noise ◽  
Velocity Dispersion ◽  
Dispersion Curves ◽  
Upper Crust ◽  
Southern Sweden ◽  
Zero Crossings ◽  
Phase Velocity Dispersion ◽  
Cross Correlations ◽  
Velocity Bias

Summary Rayleigh-wave phase-velocity tomography of southern Sweden is presented using ambient seismic noise at 36 stations (630 station pairs) of the Swedish National Seismic Network (SNSN). We analyze one year (2012) of continuous recordings to get the first crustal image based on the ambient-noise method in the area. Time-domain cross-correlations of the vertical component between the stations are computed. Phase-velocity dispersion curves are measured in the frequency domain by matching zero crossings of the real spectra of cross-correlations to the zero crossings of the zeroth-order Bessel function of the first kind. We analyze the effect of uneven source distributions on the phase-velocity dispersion curves and correct for the estimated velocity bias before tomography. To estimate the azimuthal source distribution to determine the bias, we perform inversions of amplitudes of cross-correlation envelopes in a number of period ranges. Then, we invert the measured and bias-corrected dispersion curves for phase-velocity maps at periods between 3 and 30 s. In addition, we investigate the effects of phase-velocity bias corrections on the inverted tomographic maps. The difference between bias corrected and uncorrected phase-velocity maps is small ($< 1.2 \%$), but the correction significantly reduces the residual data variance at long periods where the bias is biggest. To obtain a shear velocity model, we invert for a one-dimensional velocity profile at each geographical node. The results show some correlation with surface geology, regional seismicity and gravity anomalies in the upper crust. Below the upper crust, the results agree well with results from other seismological methods.

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.

scholarly journals The Lamb waves phase velocity dispersion evaluation using an hybrid measurement technique

2018 ◽  
Vol 184 ◽  
pp. 1156-1164 ◽  
Author(s):  
L. Draudviliene ◽  
H. Ait Aider ◽  
O. Tumsys ◽  
L. Mazeika
Keyword(s):  
Phase Velocity ◽  
Measurement Technique ◽  
Velocity Dispersion ◽  
Lamb Waves ◽  
Phase Velocity Dispersion

Multifrequency full-waveform sonic logging in the screened interval of a large-diameter production well

Geophysics ◽  
2013 ◽  
Vol 78 (5) ◽  
pp. B243-B257 ◽  
Author(s):  
Majed Almalki ◽  
Brett Harris ◽  
J. Christian Dupuis
Keyword(s):  
Phase Velocity ◽  
Velocity Dispersion ◽  
Large Diameter ◽  
Low Frequency ◽  
Production Well ◽  
Frequency Wave ◽  
Full Waveform ◽  
Phase Velocity Dispersion ◽  
Production Wells ◽  
Sonic Logging

A set of field experiments using multiple transmitter center frequencies was completed to test the application potential of low-frequency full-waveform sonic logging in large-diameter production wells. Wireline logs were acquired in a simple open drillhole and a high-yield large diameter production well completed with wire-wound sand screens at an aquifer storage and recovery site in Perth, Western Australia. Phase-shift transform methods were applied to obtain phase-velocity dispersion images for frequencies of up to 4 kHz. A 3D representation of phase-velocity dispersion was developed to assist in the analysis of possible connections between low-frequency wave propagation modes and the distribution of hydraulic properties. For sandstone intervals in the test well, the highest hydraulic conductivity intervals were typically correlated with the lowest phase velocities. The main characteristics of dispersion images obtained from the sand-screened well were highly comparable with those obtained at the same depth level in a nearby simple drillhole open to the formation. The sand-screened well and the open-hole displayed an expected and substantial difference between dispersion in sand- and clay-dominated intervals. It appears that for clay-dominated formations, the rate of change of phase velocity can be associated to clay content. We demonstrated that with appropriate acquisition and processing, multifrequency full-waveform sonic logging applied in existing large-diameter sand-screened wells can produce valuable results. There are few wireline logging technologies that can be applied in this setting. The techniques that we used would be highly suitable for time-lapse applications in high-volume production wells or for reassessing formation properties behind existing historical production wells.

Dispersion analysis for wave equations with fractional Laplacian loss operators

2019 ◽  
Vol 22 (6) ◽  
pp. 1596-1606
Author(s):  
Sverre Holm
Keyword(s):  
Phase Velocity ◽  
Fractional Derivative ◽  
Fractional Derivatives ◽  
Wave Equations ◽  
Fractional Laplacian ◽  
Velocity Dispersion ◽  
Dispersion Analysis ◽  
Phase Velocity Dispersion ◽  
Loss Term ◽  
Kronig Relation

Abstract Several wave equations for power-law attenuation have a spatial fractional derivative in the loss term. Both one-sided and two-sided spatial fractional derivatives can give causal solutions and a phase velocity dispersion which satisfies the Kramers–Kronig relation. The Chen–Holm and the Treeby–Cox equations both have the two-sided fractional Laplacian derivative, but only the latter satisfies this relation. There also exists several seemingly different expressions for the phase velocity for these equations and it is shown here that they are approximately equivalent. Causality of the Chen–Holm equation has also been a topic of some discussion and it is found that despite the lack of agreement with the Kramers–Kronig relation, it is still causal.

scholarly journals The Passive Surface Wave Methods for Shallow Engineering Exploration Based on the ESPAC Technology

2019 ◽  
Vol 131 ◽  
pp. 01041
Author(s):  
Tong Wu ◽  
Kezhu Song ◽  
Zhengyang Sun ◽  
Hongwei Zhao ◽  
Xin Hu
Keyword(s):  
Surface Wave ◽  
Phase Velocity ◽  
Velocity Dispersion ◽  
Vertical Component ◽  
Original Data ◽  
Phase Velocity Dispersion ◽  
Wave Phase Velocity ◽  
Wave Methods ◽  
Rayleigh Wave Phase Velocity ◽  
Selection Of

ESPAC method is a rapidly emerging field of seismological research, which can reflect the physical properties of the Earth’s medium. In the process of using the ESPAC method, sometimes the noise of the original data is relatively large, and the raw data of each seismometer needs to be preprocessed, including operations such as de-averaging, de-trending, re-sampling, normalization, and filtering. The selection of the normalized method and the selection of the bandwidth of the filter are particularly important, and it will produce the wrong result if not handled properly. This article attempts to use the extended spatial autocorrelation (ESPAC) method to extract Rayleigh-wave phase velocity dispersion curves from the vertical component of the seismic stations’ microtremors, and proposes feasible and effective solutions to the selection of the normalized method and bandwidth of bandpass filtering.

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