Feasibility of waveform inversion of Rayleigh waves for shallow shear-wave velocity using a genetic algorithm

Utilization of surface wave dispersive properties may be roughly divided into three steps: field data acquisition, dispersion-curve picking, and inversion of phase velocities (

The surface wave (S-wave) method has gained popularity in engineering practice for determining S-wave velocity depth profiles. A growing trend is towards the application of S-wave testing for spatially 2-D S-wave velocity tomography, ignoring the assumption of horizontally layered medium. A fourth-order velocity-stress finite difference method is used to perform numerical simulations of S-wave testing in earth models with lateral variation. Results show that the lateral heterogeneity induces a non-stationary property in the space domain, resulting in false depth-related dispersion or higher modes if conventional approach based on stationary assumption is used for the dispersion analysis. Artifacts maybe introduced in spatially 2-D S-wave velocity imaging if the effect of lateral heterogeneity is not accounted for. As a potential countermeasure, a high-lateral-resolution S-wave method is proposed to reduce the effect of lateral heterogeneity while maintaining the resolution and depth range of dispersion analysis. It consists of a walk-away survey and a phaseseaming procedure when synthesizing seismograms with different nearest source-to-receiver offset, allowing wide-wavelength dispersion analysis within a small spatial range. The proof of concept is given with several numerical examples. They show that the high-resolution S-wave method can greatly alleviate the effect of lateral heterogeneity and increase spatial resolution. r 2006 Elsevier Ltd. All rights reserved.

We performed active and passive surface wave methods at four sites in the Cherry Creek fault zone (CCFZ) in Lake Chaplain, Washington to detect the depth to bedrock below Quaternary deposits. The surface wave method was performed at four sites (PS-3, PS-1, PS-4 a nd PS-5) from east to west across the CCFZ with approximately one kilometer separations. We used a multichannel analysis of surface waves (MASW), a passive surface wave measurement using 4.5Hz geophones on a linear array (Linear-MAM) and a passive surface wave measurement using broadband accelerometers (SPAC) to obtain dispersion curves. Dispersion curves obtained by the three different methods are in excellent agreement in ranges of overlap. Maximum wavelengths obtained using the 2ST-SPAC, Linear-MAM and MASW were about 850, 200 and 50 m, respectively. As a rule of thumb, 1/2 to 1/3 of the maximum Rayleigh wave wavelength is indicative of the penetration depth of the surface wave method. The extremely deep penetration capability of the SPAC is obvious when compared to conventional surface wave methods, such as MASW or ReMi™. Phase velocities obtained from three methods were combined to produce a single dispersion curve for each site. The inversion scheme based on Genetic Algorithm was applied to the observed dispersion curves, resulting in the S-wave velocity site profiles. Results from the 2ST-SPAC survey near Sultan, Washington, near the Skykomish River (Figure 1a) provide estimates for the depth to bedrock below Quaternary sedimentary deposits as a companion study to the “Geologic map of the Lake Chaplin 7.5-minute quadrangle, King and Snohomish County, Washington” (Dragovich and others, 2014a). Four seismic survey sites marked PS-1, PS-3, PS-4 and PS-5 (Figure 1a) straddle the main strand of the Cherry Creek fault zone (CCFZ) as shown on Plate 1 of Dragovich and others (2013). Earlier study sites of Sultan B and Sultan C (Hayashi and others, 2014) are also shown for comparison (Figure 1a).

Estimation of near-surface shear-wave velocities and quality factors using multichannel analysis of surface-wave methods

The unmodelled effects of lateral heterogeneity are a primary cause of earthquake mislocation using routine methods. Approaches that account for the traveltime effects of lateral heterogeneity are a common feature of specialized studies, but some earthquake location methods have been developed that are also suitable for routine location. Here we investigate the use of one such method (3-D empirical traveltimes, ETTs) for local and regional earthquake location in an area of pronounced lateral velocity heterogeneity. We focus on New Zealand and the surrounding region due to the presence of strongly heterogeneous subduction zone environments. The New Zealand example poses significant challenges since most of the seismicity occurs outside the national seismograph network, and many of the observed ray paths traverse the high-velocity subducting slab. We show that in this environment, >60 per cent of the P and S residuals observed when a 1-D model velocity model is used stem from the resolvable lateral heterogeneity signal. For stations that have been in operation for more than five years, 85 per cent of observed residuals can be ascribed to this resolvable signal. We produce consistent 3-D traveltime corrections for all of New Zealand and the surrounding region and demonstrate their application to clusters of earthquakes occurring off the east coast of the North Island.

Joint inversion of Rayleigh and Love wave dispersion curves for improving the accuracy of near-surface S-wave velocities

Shuffled complex evolution approach for effective and efficient surface wave analysis

We present a method that utilizes the Multichannel Analysis of Surface Waves (MASW) technique and a standard common depth point (CDP) roll-along acquisition format similar to conventional petroleum exploration seismic data acquisition to construct a vertical section of the near-surface shear (S)-wave velocity field. A one-dimensional (1-D) S-wave velocity vs. depth plot is obtained by inverting phase velocities using the MASW technique. This 1-D profile appears to be most representative of the materials directly below the middle of a geophone spread. Multiple 1-D plots of S-wave velocity vs. depth are generated as the source and receivers roll along a survey line. A two-dimensional (2-D) vertical cross-section of S-wave velocity can be constructed by contouring grids produced by combining all the 1-D S-wave velocity profiles that are a function of the middle point of geophone spread (x) and depth (z). The combination of inverting the phase velocity for S-wave velocity and the standard CDP roll-along acquisition format makes this a very effective and time-efficient method of imaging two-dimensional Swave velocity along a survey line. There are several advantages that make this method attractive in real world applications. 1. The method focuses on high-frequency ( ≥ 2 Hz) ground roll to provide a 2-D near-surface S-wave velocity map and to detect targets significantly shallower than feasible with other acoustic techniques. 2. That ground roll, which is acquired by the multichannel acquisition method, has a high signal-to-noise ratio, allowing 2-D images to be obtained in extremely noisy environments. 3. The method uses the standard CDP roll-along acquisition format, which provides an efficient way to acquire large quantities of broadband surface wave data along a line. 4. The method utilizes the redundancy of the standard CDP roll-along acquisition format so that it not only provides a reliable way to verify inverted S-wave velocities, it also reduces the ambiguity of inverted S-wave velocities. 5. A 2-D display of S-wave velocity can be produced easily and quickly by contouring the inverted S-wave velocity to provide a map of the S-wave velocity field. 6. 2-D data processing techniques, such as regression analysis, could easily be applied to a vertical S-wave velocity section to enhance local anomalies (gas or oil fields, voids, tunnels, etc.). More than five thousand shots of MASW data have been acquired and processed producing more than forty vertical near-surface S-wave velocity sections since 1997. Four real world examples demonstrate the usage of the method.

The multi-channel analysis of surface waves (MASW) is a widely employed surface wave method. The fundamental mode inversion is the usual scheme in MASW, because separating the fundamental mode from other high modes is feasible with an adequately long array. However, the extracted fundamental mode represents only part of the dynamic characteristics, it may deviate from the theoretical fundamental mode due to truncation effect, and part of it may correspond to another higher mode or leaky mode, resulting in mode misidentification. Conversely, the spectral analysis of surface waves (SASW) method features a more rigorous inversion scheme by matching the effective mode, but it may suffer from the tricky phase-unwrapping in the dispersion data reduction. This study introduces an improved dynamic response solution for elastic-layered media subjected to vertical loads. The proposed dynamic response solution is fast and accurate, facilitating the full wavefield inversion in terms of the frequency-velocity spectrum. The MASW frequencyvelocity spectrum inversion considers testing configuration and comprehensively models all wave phenomena, including near-field effect, truncation effect, and leaky waves. The MASW frequency-velocity spectrum inversion merges the convenience of MASW dispersion analysis with the rigorous inversion scheme adopted by SASW. The new MASW frequency-velocity spectrum inversion is compared with the SASW effective mode inversion and MASW fundamental mode inversion. The results show that both SASW effective mode inversion and MASW frequency-velocity spectrum inversion produce better inverted results than the MASW fundamental mode inversion, while the process of MASW frequency-velocity spectrum inversion is more convenient and robust. Finally, a field example is used to demonstrate the applicability of frequency-velocity spectrum inversion.

Highly dispersive surface waves resulting from the combination of strong lateral seafloor heterogeneities, shallow water depths and hard sea bottom severely degrade seismic reflection data quality. Considering that seismic signals are nonstationary and surface waves have various spectra over time, we proposed S-transform-based time frequency wavenumber analysis technique which allows the dynamic analysis of spectrum over time. The data is first transformed from the time-space domain to the time-wavenumber domain through one-dimensional Fourier transform over the spatial variable, then the variable-factor S-transform is applied over time. Nonstationary filtering is then designed to identify and separate surface waves in complex wavefields, based on its low frequency and low velocity properties, in the time-frequency-wavenumber (TFK) domain. Application to field data illustrates that with this technique, not only is the surface wave effectively suppressed, but also the reflective signals are enhanced, which confirm the validity of the method.

Reliable, stable, and internally consistent moment magnitude (Mw) estimates are essential for seismic hazard assessment and earthquake source characterization. Full waveform inversion provides physically robust seismic moment estimates; however, its applicability is often constrained by data quality, network geometry, and modeling assumptions. Conversely, coda-based approaches are a more efficient alternative that are less sensitive to radiation pattern and path effects. This study presents a systematic comparison between coda-derived moment magnitudes (Mw-coda) estimated using the Qopen framework and those (Mw-ISOLA) obtained from moment tensor inversion conducted through the ISOLA software.Analysis is based on the same dataset examined by Özkan et al. (2024), comprising 303 local earthquakes (2.5 ≤ ML ≤ 5.7) recorded by 49 broadband stations in the Sea of Marmara region, NW Türkiye. Qopen is utilized to jointly invert S-wave and coda-wave envelopes by employing Radiative Transfer Theory. This process yields frequency-dependent attenuation parameters and coda-derived source spectra, from which the Mw-coda is estimated. For a subset of these events with sufficient waveform quality and azimuthal coverage, independent seismic moment estimates are obtained through time-domain waveform inversion using ISOLA.Overall, we aim to evaluate the agreement and consistency between Mw-coda and Mw-ISOLA in terms of magnitude scaling, scatter, and potential systematic bias, with particular emphasis on magnitude range, source depth, and signal-to-noise conditions in a tectonically complex region characterized by strong lateral heterogeneity and frequency-dependent attenuation.

In some areas, the estimation of static corrections for land seismic data is a critical step of the processing workflow. It often requires the execution of additional surveys and data analyses. Surface waves (SWs) in seismic records can be processed to extract local dispersion curves (DCs) that can be used to estimate near-surface S-wave velocity models. Here we focus on the direct estimation of time-average S-wave velocity models from SW DCs without the need to invert the data. Time-average velocity directly provides the value of one-way time, given a datum plan depth. The method requires the knowledge of one 1D S-wave velocity model along the seismic line, together with the relevant DC, to estimate a relationship between SW wavelength and investigation depth on the time-average velocity model. This wavelength/depth relationship is then used to estimate all the other time-average S-wave velocity models along the line directly from the DCs by means of a data transformation. This approach removes the need for extensive data inversion and provides a simple method suitable for industrial workflows. We tested the method on synthetic and field data and found that it is possible to retrieve the time-average velocity models with uncertainties less than 10% in sites with laterally varying velocities. The error on one-way times at various depths of the datum plan retrieved by the time-average velocity models is mostly less than 5 ms for synthetic and field data.

Due to the diverse lithology and complex pore structure of the carbonate reservoirs, the conventional shear wave (S-wave) velocity prediction method is insufficient in mining information, resulting in low accuracy. Therefore, CatBoost is proposed to predict S-wave velocity in complex carbonate reservoirs. Different from the point-to-point learning of continuous variables by traditional machine learning, CatBoost can discover the mixed variables composed of continuous wireline logs and discrete local sequence features, mine the internal relationship between wireline logs and S-wave velocity, build a high precision S-wave velocity prediction model. In the research of the carbonate reservoir in Sudong area of Sulige gas field, sixteen logging parameters sensitive to S-wave velocity are selected, and local wireline logs and lithologic sequence information are introduced to construct a prediction model based on CatBoost. Compared with traditional machine learning, such as SVM, BP neural network, and conventional Xu-Payne petrophysical model, the RMSE of the S-wave prediction model based on CatBoost is only 2.87µs/m but the accuracy reaches 97.59%. The results show that the S-wave prediction model based on CatBoost is more suitable for actual geological distribution and provides a new idea for further research on complex reservoirs.

Crustal and upper mantle structure in the intracratonic Paraná Basin, SE Brazil, from surface wave dispersion using genetic algorithms

This study contains the finding of geophysical investigations conducted at the proposed science complex site at Lagos State University, Ojo, Lagos, Nigeria. Surface wave and seismic refraction tests are non-invasive seismic techniques and have been used to determine the shear wave velocity profile of soil deposits. The methods provide a simplified characterization of subsurface in two-dimensional (2D) (distance and depth) profiles. Seismic records obtained were processed/analyzed by Seis-Imager software to obtain one-dimensional shear wave velocity (Vs) distribution. Multiple Vs obtained were integrated and used to construct two-dimensional Vs map. The measured P- and S-wave velocities were also used to estimate Poisson’s ratio, rigidity modulus, and N-values. The study had shown that the area investigated composed mainly of loose sediments (clay formation) to the depth of 12 m with P-wave velocity ranging between 125 and 205 m/s and corresponding S-wave velocity between 60 and 100 m/s. The results presented in this study will be vital information for the engineers in construction of the proposed science complex.