An Unsupervised Wavelet Transform Method for Simultaneous Inversion of Multimode Surface Waves

Section 1 Physical properties and laboratory measurements.- Shear waves in marine sediments-bridging the gap from theory to field applications (Opening paper).- Surface waves in poro-viscoelastic marine sediments.- An investigation of causality for Biot models by using Kramers-Kronig relations.- Soil properties for shear wave propagation (Invited).- The relevance of shear waves for structural subsurface investigations.- Experimental investigation of seismic surface waves in the seafloor.- Laboratory studies on pulsed leaky Rayleigh wave components in a water layer over a solid bottom.- Assessment of shear strength of the sea bottom from shear wave velocity measurements on box cores and in-situ.- Numerical modelling and laboratory experiments on underwater sound propagation over a shear supporting bottom.- A review of laboratory shear wave techniques and attenuation measurements with particular reference to the resonant column (Invited).- Relationship between acoustic and mechanical properties of two marine clays.- A laboratory method to investigate shear waves in a soft soil consolidating under self weight.- Laboratory measurements of acoustic properties of periplatform carbonate sediments.- Comparison of measured compressional and shear wave velocity values with predictions from Biot theory.- Wave velocities in sediments.- Shear wave attenuation in unconsolidated laboratory sediments.- Shear wave velocities of glacio-marine sediments: Barents Sea.- Rock acoustics: relevance of the porous viscoelastic model.- Influence of stress state and stress history on acoustic wave propagation in sedimentary rocks.- Section 2 Field experiments and interpretation.- A summary of DREA observations of interface waves at the seabed.- Observations of the relative contributions of waterborne and sediment paths to the received acoustic signal.- Shear-wave anisotropy in marine sediments around Britain from surface sources.- Refraction measurement of shear wave anisotropy in shallow marine sediments and implications for reflection processing.- Spatial variability in ground motion: effects of material heterogeneity in seafloor sediments.- Implications of deep-water seismometer array measurements for Scholte wave propagation.- Shear wave velocity structure from interface waves at two deep water sites in the Pacific ocean.- The effects of shear velocity structure on seafloor noise.- Concurrent observations of directional spectra of ocean surface waves and microseisms from an ocean subbottom seismometer (OSS) array.- Wave propagation in a borehole (Invited).- Application of shear wave measurements in boreholes.- Experience with the seismic cone penetrometer in offshore site Investigations.- Comparison of techniques for shear wave velocity and attenuation measurements.- Shear wave velocity gradients in near-surface marine sediment.- ISSAMS: an in situ sediment acoustic measurement system.- Small-scale in situ measurements of S-H velocity in surficial sedimentary deposits: localised textural and biological controls.- In situ measurements of shear-wave velocity in ocean sediments.- Seafloor shear wave velocity data acquisition: procedures and pitfalls.- Mapping of the sea bed via in situ shear wave (SH) velocities.- Observations of split shear-waves from young ocean crust.- Estimation of shear-wave speed in ocean-bottom sediments by comparing oblique-angle reflectivity measurements with normal incidence data.- SedimentQpfrom spectral ratios of converted shear reflections.- Constraints on shear velocities in deep-ocean sediments as determined from deep-tow multichannel seismic data.- Changes inPandSvelocities caused by subduction related sediment accretion off Washington/Oregon.- Compressional and shear wave velocities in the upper crust.- Sedimentary shear modulus and shear speed profiles from a gravity wave inversion.- Measurements of compressional wave and shear wave speeds, attenuation, permeability, and porosity in marine sediments.- Sea-bed shear moduli from measurements of tidally induced pore pressures.- Section 3 Modelling and inversion techniques.- Excess attenuation in low-frequency shallow-water acoustics: a shear wave effect? (Invited).- Sensitivity of bottom loss to attenuation and shear conversion.- The effect of shear wave attenuation on acoustic bottom loss resonance in marine sediments.- The influence of sediment rigidity on the plane-wave reflection coefficient.- Shear wave conversion due to subbottom facets.- A seismo-acoustic finite element model for underwater acoustic propagation.- Finite difference modelling of shear waves.- A stable higher-order elastic parabolic equation with application to Scholte wave propagation.- ELASTIC PE: a parabolic approximation for propagation modelling of shear wave effects in sediment layers.- Computation of shear waves by integral equations methods in stratified media.- Normal modes identification in shallow water using spectral analysis: theory and experiments.- Estimation of geoacoustic properties by inversion of acoustic field data (Invited).- A fast simulated annealing algorithm for the inversion of marine sediment seismo-acoustic parameters.- Determination of the sediment shear speed profiles from phase and group velocity dispersion data of SH wave.- Measurement of the elastic properties of the ocean bottom by inversion of reflection amplitude data.- Surface wave inversion for shear wave velocity (Invited).- Determination of shear velocity profiles by inversion of interface wave data.- Using synthetic seismograms to determine shear wave velocities in sediments from ocean bottom seismometer refraction observations.- Analytical investigation of seismic surface waves in the seafloor.- List of Participants.- Author Index.

Dispersive characteristic measurement of multi-layer cement mortar slabs using SASW method and neural network

Shear and compressional wave velocities, coupled with other petrophysical data, are very important for hydrocarbon reservoir characterization. In situ shear wave velocity (Vs) is measured by some sonic logging tools. Shear velocity coupled with compressional velocity is vitally important in determining geomechanical parameters, identifying the lithology, mud weight design, hydraulic fracturing, geophysical studies such as VSP, etc. In this paper, a correlation between compressional and shear wave velocity is obtained for Gachsaran formation in Maroon oil field. Real data were used to examine the accuracy of the prediction equation. Moreover, the genetic algorithm was used to obtain the optimal value for constants of the suggested equation. Furthermore, artificial neural network was used to inspect the reliability of this method. These investigations verify the notion that the suggested equation could be considered as an efficient, fast, and cost-effective method for predicting Vs from Vp.

Pore-scale modelling of elastic properties in hydrate-bearing sediments using 4-D synchrotron radiation imaging

Indirect determination of shear wave velocity in slow formations using full-wave sonic logging technique

A number of strategies exist to account for the epistemic uncertainty and aleatory variability in shear-wave velocity (Vs) profiles used in site response analyses. Epistemic uncertainty may be accounted for by using median and bounding-type profiles (e.g., ±20%), while aleatory variability may be accounted for by using Vs randomization procedures. A robust, quantitative method to help judge how well these statistically derived Vs profiles represent actual subsurface stiffness or layering conditions is currently not available. This paper presents a surface-wave dispersion approach for evaluating statistical models meant to account for Vs uncertainty in site response. Specifically, surface-wave dispersion data from two geologically disparate sites were used to generate 1,000 Vs profiles and layered earth models whose theoretical dispersion curves fit within the uncertainty bounds of the experimental data collected at each site. Additionally, theoretical dispersion curves generated from statistical ...

Lamb waves are guided dispersive waves propagating in free plate structures (Lamb, 1917). By matching theoretical multimodal Lamb wave dispersion curves with experimental ones, shear wave velocity (Vs), Poisson's ratio (v), and thickness (d) of the tested plak structure can be evaluated. In this expanded abstract a practical approach for NDT of pavements and concrete structures utilizing multiple modes of Lamb wave dispersion curves is presented. Both the measuring procedure and the analysis scheme is described. A complete description of how to calculate theoretical Lamb wave dispersion curves and more details on this study were given in the original manuscript (Ryden et al. 2003).

A combination of geophysical techniques can yield estimates of several physical properties versus depth. An example is presented for a thick sequence of sediments in Middle Valley near the present spreading axis of the Juan de Fuca Ridge. We have computed the porosity, temperature, and thermal conductivity versus depth by combining the results of seafloor electrical and heat flow surveys. The electrical resistivity of the sediments is empirically related to the porosity of the medium and to the pore fluid electrical conductivity, which is in turn sensitive to the temperature. The temperature profile is determined from the heat flow and the thermal conductivity. The latter is determined from calculated porosity and estimates of the constituent mineral and pore fluid thermal conductivities. The measured surface heat flow is assumed to be, and the resistivity has been determined to be, approximately constant with depth. The computation of the variation of temperature, porosity, and thermal conductivity with depth yields physically realistic and reasonable results. Other physical properties (void ratio, bulk density, water content, compressional wave velocity) are estimated from the porosity. The shear wave velocity is calculated empirically from the compressional wave velocity, and Poisson's ratio is then computed from the compressional and shear wave velocities. The results are in good agreement with values derived for similar rapidly deposited sediment sequences elsewhere, but the model calculations indicate that Deep Sea Drilling Project measurements may be biased toward higher‐porosity samples.

The accurate prediction of site effects is closely related to the quality of the seismic site characterization. Furthermore, increasingly probabilistic design procedures require not only a single seismic velocity profile, but a suite of profiles that rigorously accounts for epistemic and aleatory uncertainties. The quantification of these uncertainties is particularly important for non-invasive site characterization techniques that require inversion, such as surface wave methods, as the non-uniqueness of the derived velocity profiles depends on the uncertainties of the experimental data, which are dependent on the type and number of non-invasive measurements as well as the site's geologic setting. This work expands upon previous efforts to develop shear wave velocity (Vs) profile’s whose corresponding uncertainty is consistent with that of the experimental data and that rigorously address the non-uniqueness in the inverse problem. In particular, this work addresses three key points. First, how experimental data from multiple active-source and/or passive-wavefield surface wave arrays can be statistically combined to quantify site-specific aleatory uncertainty. Second, how multiple inversion parameterizations can and should be used to quantify epistemic uncertainty in the inverse problem. Third, how site-specific statistical models can be derived from non-invasive site characterization efforts as an alternative to existing Vs randomization techniques commonly used in practice. These advances are demonstrated at the Garner Valley Downhole Array (GVDA) site located in southern California. As a result of this study, new uncertainty-consistent shear and compression wave velocity profiles have been produced at the GVDA site for use in future forward and backward prediction efforts.

The dispersion curves of surface waves have been widely used for the retrieval of subsurface structures. Because the surface-wave dispersion is not sensitive to Vp, classical dispersion inversion can only retrieve Vs structures. To retrieve Vp, the dispersion of guided-P waves, which belong to leaky waves, should be considered. Due to the difficulty in forward modeling, the quantitative analysis of the leaky-wave dispersion curves has been rarely reported. In this study, we first derive the sensitivity analysis method of the leaky-wave dispersion based on previously proposed the semi-analytical spectral element method. Then the quantitative sensitivity analysis of leaky-wave dispersion curves is carried out, which confirms the ability of guided-P wave dispersion to constrain the velocity structures. With the theoretical analysis, we propose a joint inversion method based on surface and guided-P wave dispersion curves, which can simultaneously retrieve Vp and Vs. To verify the effectiveness, the proposed joint inversion has been applied to different kinds of field data including ocean bottom seismometer data with active sources and the seismic data of Nevada in the United States in 2008. Both of the inversion tests show that the joint inversion of surface- and leaky-wave dispersion can effectively constrain the velocity structure of Vp and Vs at the same time, which helps to obtain more complete and accurate models than the traditional surface wave dispersion inversion.

Examples are presented which show that the velocity, amplitude, attenuation and apparent frequency of several acoustic waves can be recorded in the borehole. Examination of such recordings, termed "character" logs, indicates that the wave types observed include a refracted compressional wave and a wave which travels with formation shear velocity.Laboratory data are used to show that compressional and shear wave velocities are dependent on porosity, effective stress and lithology; but that the change in reciprocal velocity per unit change in porosity is larger for shear waves than for compressional waves. We, therefore, conclude that the accuracy of porosity determinations can sometimes be improved by use of shear wave velocities, provided that the shear wave amplitudes are large enough to delineate the shear arrival from the preceding compressional arrival on the character log. Borehole data are presented which show that the difference between shear wave and compressional wave reciprocal velocities can be used to predict porosities. This is a refinement which may allow the prediction of porosities from single-receiver acoustic logs without introduction of errors from borehole fluid travel-times. Laboratory and field data are presented to show that the relationship between compressional and shear wave velocities can be used to indicate lithology.An example is presented to show that fractures usually cause a greater reduction in borehole shear wave amplitudes than in compressional wave amplitudes, an effect which may offer a more reliable means of detecting fractures.The complexity of the borehole acoustic wave train can make presently available cement bond logs highly sensitive to the gate and bias settings used. The character log offers a means to circumvent possible misinterpretations by recording all amplitudes, from which the interpreter can select the appropriate data for evaluating the cement bond.Character logs may also be used as a quality control for open-hole transit-time logs when existence of small compressional wave amplitudes interferes with the proper functioning of bias-controlled timing devices.Evaluation of the potential uses of character log data is not complete; but a character log presented in a form convenient for routine use would be a desirable addition to currently available logs. To summarize, possible applications for such a log in formation evaluation include the followingquality control of transit-time logs,refinement of porosity predictions,determination of lithology,improvement of fracture detection andimprovement of cement bond evaluation. Suggestions are made regarding the requirements for a sufficient but practical character log for routine use. Introduction Acoustic logs have become a widely used porosity tool in formation evaluation. In addition, there is a growing application of acoustic logs in cement bond evaluation and fracture detection. These applications have mainly involved the use of logs of first-arrival transit times and amplitudes and have not included detailed studies of the complete signal.The purpose of this paper is to show that significant benefits in formation evaluation can be gained by a more complete use of the acoustic wave train generated in the borehole by an acoustic logging tool. We hope that this discussion will also stimulate further development of logs suitable for routine use so that these benefits may be realized.Examples of acoustic wave train logs, termed "character" logs, are presented to show that several identifiable acoustic waves are present in the borehole. The measurable characteristics of these acoustic waves and some of their relations to formation properties of interest are also discussed. The more obvious potential uses of character logs are listed, and some suggestions are made regarding the requirements for a sufficient but practical character log for routine use. CHARACTER LOGS Some 10 years ago, Vogel and Summers and Broding noted that the signals received uphole from an acoustic logging tool located in a borehole had a number of interesting characteristics. The logging tool consisted of two or more pressure transducers spaced on an acoustically insulated body (Fig. 1a). One of the pressure transducers was used as a transmitter to generate pressure waves in the borehole fluid. The other transducer served as a receiver to detect any pressure waves reaching it in the borehole. The receiver then converted these pressure waves to electrical signals which were transmitted to the surface and displayed on an oscilloscope as a record of time vs receiver-signal amplitude. Fig. 1b is a schematic representation of a typical record. JPT P. 639^

SUMMARY Poisson's ratio is a commonly used parameter in geotechnical engineering research. Although most studies on its dynamic behaviour have been performed using laboratory tests, which are not necessarily representative of the anticipative soil behaviour in practice, especially nonlinear behaviour. By contrast, the in-situ studies using seismic data are limited and inadequate. Hence, in this study, we first performed the in-situ estimations of Poisson's ratios at various strains for seven research cases by applying seismic interferometry to seismic data from three seismic downhole arrays. Then, we proposed a proxy named equivalent water content, Weq, which was calculated by using site information and used to evaluate the influence of groundwater. Finally, by calculating the Weq for each research case, the in-situ dynamic behaviours of Poisson's ratio and the ratio between compression and shear wave velocities were investigated for sites with low shear stiffness and high water content. It was found that there were significant relationships between the proposed proxy and the in-situ behaviours of Poisson's ratio and the ratio between compression and shear wave velocities. The small-strain Poisson's ratio and the ratio between small-strain compression and shear wave velocities increased with Weq at the change rates, which gradually decreased and increased, respectively. The nonlinear variation of Poisson's ratio at each shear strain decreased with increases in Weq and shear modulus ratio at the change rates, which gradually decreased and increased, respectively. By constructing an analysis model, three formulae were further proposed to describe the above relationships, which can be utilized to build the empirical equations for preliminarily estimating the small-strain Poisson's ratio, the ratio between small-strain compression and shear wave velocities and the nonlinear variation of Poisson's ratio without requiring compression wave velocity.

In many oil fields only the BHC logs (borehole compensated sonic tool) are available to provide interval transit time (Δtp), the reciprocal of compressional wave velocity VP.
 To calculate the rock elastic or inelastic properties, to detect gas-bearing formations, the shear wave velocity VS is needed. Also VS is useful in fluid identification and matrix mineral identification.
 Because of the lack of wells with shear wave velocity data, so many empirical models have been developed to predict the shear wave velocity from compressional wave velocity. Some are mathematical models others used the multiple regression method and neural network technique.
 In this study a number of empirical models were considered to predict VS from VP. The models had been correlated and a general equation, based on statistical method, was established for carbonate rocks.
 The proposed equation, then, was examined using log data and good results observed.

Data-driven shear wave velocity prediction model for siliciclastic rocks

An evaluation of empirical and rock physics models to estimate shear wave velocity in a potential shale gas reservoir using wireline logs