Shear Wave Velocity Estimation Research Articles

On a new method of estimating shear wave velocity from conventional well logs

Shear wave velocity is a critical parameter for the characterization of hydrocarbon reservoirs. Compared with compressional wave velocity which almost exist in every well, shear wave velocity hasn't been recorded in those days for the older wells due to the lack of logging equipment or limited funds. Furthermore, measuring shear wave velocity is fairly time- and money-consuming as it can only be gained by the analysis of core samples conducted in the lab or from the dipole sonic imager (DSI). To cope with the above puzzles, a new methodology, by integrating extreme learning machines (ELM) and technique of mean impact value (MIV), is proposed in this paper with the support of log data collected from two wells located in unconventional shale gas reservoir in Ordos Basin, China. Based on mean impact value, a well-trained ELM model is taken to identify optimal well logs and five well logs are identified to provide the significant and valid information for the estimation of shear wave velocity. 3201 data points collected from well L4 are used in constructing the model. Compared with artificial neural network used in the former studies Levenberg-Marquardt algorithm (ANN-LM), the ELM model's prediction accuracy has been evaluated, the results indicates that the ELM model outperforms ANN-LM model with faster calculating speed and better performance. Additionally, the efficiency of the model proposed here is well investigated by using another well with 3201 data points. Through the comparison among ELM, support vector regression (SVR), convolutional neural network (CNN) and four widely known empirical formulas, what can be concluded is that ELM model is more efficient in fast calculation and high precision. From the result, it can be demonstrated that the use of ELM model, combined with the analysis of mean impact value (MIV), is a more efficient and promising method for shear wave velocity estimation process from conventional well log data, which can be recognized as a promising tool with an extended application. And this research can be applied into a software system for rapid acquisition of shear wave velocity logs.

Estimativa de Velocidade de Onda de Cisalhamento pela Inversão Conjunta de Curvas HVSR e f-k sob a Hipótese do Campo Difuso: um Estudo de Caso do Deslizamento de Sobradinho

Brazilian landslides are characterized as shallow, clay rich and are commonly triggered by the summer rainfalls. Therefore, the landslide geological information, such as shear surface location, has a paramount importance in their mechanism comprehension. The most adapted methods for the estimation of shear wave velocity profile are borehole stratigraphic logs or Standard Penetration Test (SPT) and Cone Penetration Test (CPT). However, the present study applied shear wave velocity estimation of Sobradinho landslide (SLS) by a joint inversion of horizontal to vertical spectral ratio (HVSR) curve and dispersion curve (DC) extracted from frequency-wavenumber (f-k) analysis of ambient noise records. HVSR curves at all the stations in the area exhibit the ubiquitous resonance frequency peak at 2 Hz indicates that at these stations the substratum is common. The f-k results for E-W component let us obtain an acceptable DC between 5 and 7 Hz range. Finally, joint inversion was interpreted based on the diffuse field assumption. The initial model was proposed to be a three-layered over a half-space. Results of joint inversion indicate that the substratum is at 24 m depth, with Vs values close to 1500 m/s. DC defines two layers overlaying the substratum: superficial layer with velocities near to 200 m/s (7m thick), and the second layer with Vs value of 1000 m/s. We think that abrupt rheology (stiffness) change between the first and the second layer could provide an evidence of the landslide re-activation during moderate to strong rainfall events. The proposed methodology will prove a reconnaissance survey for the detailed geotechnical investigations that will confirm the obtained results.

Estimating shear wave velocity of soil using standard penetration test (SPT) blow counts in Mashhad city

This study investigates the correlation between shear wave velocity ( $$V_{\mathrm{S}}$$ ) and standard penetration test blow counts (SPT-N value) in all soil types, gravelly soil, sandy soil and clayey soil for Mashhad city in the north eastern region of Iran. The $$V_{\mathrm{S}}$$ data used were measured through downhole method in 84 construction projects (in 88 boreholes). From among collected data, 424 pairs of $$V_{\mathrm{S}}$$ -SPT recorded in one depth were used for regression analysis. The obtained results showed that the N-value had a critical role in estimating $$V_{\mathrm{S}}$$ and soil type was less effective in this regard. These findings are in line with the findings of the previous studies. Regression equations obtained in this study were compared with correlations from previous studies. There was a relative similarity between the previously published and the new regression equations for Iranian soils. Although almost all correlations follow a similar trend, there are significant differences between new equations and correlations reported for other countries. The regression coefficients of the new equations show the acceptable capability of the suggested correlations in estimating $$V_{\mathrm{S}}$$ through SPT-N value. Therefore, these equations can be used to estimate $$V_{\mathrm{S}}$$ for the soils of the current study area and for other similar areas. Moreover, $$V_{\mathrm{S30}}$$ was used for site classification of the study area as per National Earthquake Hazard Reduction Program (NEHRP) guidelines and it was shown that a major portion of the city comes under site class C and other locations are categorised as site class D.

Shear-wave velocity estimation for calciferous sandy shale formation

Shear-wave velocity estimation for calciferous sandy shale formation

A kernel smoothing algorithm for ablation visualization in ultrasound elastography

Three-dimensional visualization of tumor ablation procedures have significant clinical value because the ability to accurately visualize ablated volumes can help clinicians gauge the extent of ablated tissue necrosis and plan future treatment steps. Better control over ablation volume can prevent recurrence of tumors treated using ablative procedures. This paper presents a kernel based smoothing algorithm called MatérnSmooth to reconstruct shear wave velocity maps from data acquired through ultrasound electrode vibration elastography. Shear wave velocity estimates are acquired on several intersecting imaging planes that share a common axis of intersection collinear with the ablation needle. An objective method of choosing smoothing parameters from underlying data is outlined through simulations. Experimental validation was performed on data acquired from a tissue mimicking phantom. Volume estimates were found to be within 20% of the true value.

Ambient noise data selection based on the asymmetry of cross-correlation functions for near surface applications

Passive surface wave methods utilizing traffic noise have been studied in recent years to estimate shear wave velocity in urban near-surface explorations. Suitable processing scheme is necessary for the emergence of coherent signal, and even to account for the azimuthal effects in acquired noise data. We propose a new ambient noise data selection technique based on the asymmetry of the cross-correlation functions to refine the quality of data processing in the complex city environment. The asymmetry coefficient is defined by the logarithmic energy ratio of the casual and acausal surface waves to measure the correlation asymmetry, and two kinds of symmetric functions are taken into account to establish the screening conditions. The underlying physics for the symmetries of the correlation functions are demonstrated to prove the feasibility of our algorithm. Two numerical tests suggest that the bidirectional inline sources are adequately highlighted, and the high velocity anomalies caused by the offline sources are eliminated by our method. Furthermore, the significances of the applications of time window and normalization are investigated to improve the reliability of the algorithm. We also apply the method to three-component field data acquired from the city pavement. The comparisons between the results of raw and selected data confirmed that the random noise and the artifacts can be effectively suppressed, and the dispersion energy trends emerge clearly and become more convergent toward the lower frequency. Finally, our method is concluded to be practical for urban bidirectional traffic noise.

Prediction of S-wave velocity by a hybrid model based on the Greenberg-Castagna equation

In geophysics, more specifically in rock physics and petrophysics, empirical equations play an important role in data regularization, especially in datasets that are difficult to acquire in situ. In terms of well logging, a common scenario is the absence of shear wave slowness data, which can be handled by different methods that aim filling data gaps (regularization). This work consists of the application of a hybrid approach (based on Greenberg-Castagna method) to estimate S-wave velocity in brine-saturated lithologies on well-log datasets. The combination of local polynomial regressions with a fluid substitution analysis (Gassmann's equation) leads to an effective method of estimating shear wave velocity (VS) from compressional wave velocity (VP) when information about lithology and saturation are available. Well-log datasets (from the Norwegian Sea region) are used to demonstrate the feasibility of our methodology and show its usefulness for dataset regularization based on the local information. We selected learning and test wells from the Norne Field, where Lower to Middle Jurassic sandstones behave as hydrocarbon reservoirs. Our results show that the best fitting between the measured and predicted S-wave velocities were obtained from the modified Greenberg-Castagna method (in this work, named calibrated relation), also verified on a well from the North Viking Graben (validation dataset).

Robust downhole ultrasonic pitch-catch measurements of compressional and shear wave velocities

Probing acoustic wave velocities of earth formations, both in azimuth and radius, is important when evaluating anisotropy and/or heterogeneity of the formations. A conventional approach for evaluating these complex formations is to employ a sonic logging tool that operates from approximately 0.1 kHz to 20 kHz with an approximately 600 mm spatial resolution. With these standard sonic tools, evaluating formation acoustic wave velocities with an order smaller spatial resolution to detect thin beds and/or azimuthal variation of formation properties is very challenging. To overcome this challenge, this paper discusses an ultrasonic pitch-catch measurement that can be applied to a downhole acoustic tool. Downhole conditions are typically harsh, especially for ultrasonic frequencies. Thus, a robust measurement system is required that maximizes the signal-to-noise ratio. One of the ways to do this is to minimize the distance between the transmitter and the array receiver (and the receiver-receiver spacings of the array). Numerical modeling corroborated by experimental study indicates such a measurement system can primarily detect refracted compressional waves and surface mode waves related to the pseudo-Rayleigh mode. Characteristics of the pseudo-Rayleigh mode measured with such system and a way to estimate shear wave velocity from the measured mode are discussed.

Assessing shear wave velocity profiles using multiple passive techniques of Shillong region of northeast India

Shillong region of northeast India falls under seismic zone V. Being a commercial hub, urbanization in this study region is at its peak. In order to qualitatively assess the subsurface velocity profiling of this area, we have blended two robust techniques, namely spatial autocorrelation (SPAC) and frequency wavenumber (FK) method. Corresponding to array noise data collected at five sites, situated in the close proximity of boreholes, we have evaluated VS and VP as well. The shear wave velocity estimates yielded by these techniques are found to be consistent with each other. The computed Vs values up to depth of 30 m are observed to be in the range of 275–375 m/s, in most of the sites which implies prevalence of low-velocity zone at some pocket areas. The estimates so found are systematically analyzed and implications are outlined. The results were corroborated by substantial evidence of site geology as well as geotechnical information.

Shear-wave velocity estimation using a combination of ambient noise from small aperture array and small-scale active seismic measurements: a case study in the area of the natural gas fields of Northern Germany

In recent years, numerous induced seismic events have occurred in the proximity of the natural gas field in Northern Germany. To monitor the seismicity and to asses the seismic hazard potential, a local monitoring network was installed in the area. Focusing on the seismicity hazard assessment, a major challenge is the characterisation of potential site effects due to local soil characteristics. This is quantitatively performed by estimating the shear-wave velocity (V s) variation with subsurface layer thickness. Such local effects can only be covered with a coarse spatial resolution due to the limited number of monitoring stations. Profiles were determined at three test sites (Langwedel, Walle and Bomlitz) by using a combined approach of small aperture 2D array ambient noise and small-scale active 1D measurements. The high-resolution frequency-wavenumber (HRFK), spatial autocorrelation (SPAC) and multichannel analysis of surface waves (MASW) methods were applied to the recorded ambient noise and active seismic data using various array sizes supplemented by the active measurements. This jointly allowed obtaining phase velocity dispersion curves covering a wide frequency range from 2 up to 32 Hz. The inversion of the obtained dispersion curves results in average S-wave velocity profiles down to depths of 70 m, identifying thin near-surface layers of a few meters as well as thicker layers of tens of meters in greater depth. A comparison with available borehole data shows a good correlation with the layering. Additionally, to asses the impact of a seismic event at the test sites, PGV estimations for various seismic events were performed. The final results of the test surveys demonstrate that the combined approach represents a suitable tool for near-surface characterisation, which can be used to improve the seismic hazard assessment in the area of the natural gas fields in Northern Germany.

3D elastic tensor imaging in weakly transversely isotropic soft tissues

We present herein 3D elastic tensor imaging (3D ETI), an ultrasound-based volumetric imaging technique to provide quantitative volumetric mapping of tissue elastic properties in weakly elastic anistropic media. The technique relies on (1) 4D ultrafast shear wave elastography (SWE) at very high volume rate (e.g. > 8000 Hz, depending only on the imaging depth), (2) a volumetric estimation of shear wave velocity using the eikonal equation and (3) a generalized 3D elastic tensor-based approach. 3D ETI was first evaluated using numerical simulations in homogeneous isotropic and transverse isotropic media. Results showed that 3D ETI can accurately assess tissue stiffness and tissue anisotropy in weakly transversely isotropic media (elastic fractional anisotropy coefficient < 0.34). Experimental feasibility was shown in vitro in a transverse isotropic phantom. Quantification of the elastic properties by 3D ETI was in good agreement with 2D SWE results performed at different orientations using a clinical ultrafast ultrasound scanner. 3D ETI has the potential to provide a volumetric quantitative map of tissue elastic properties in weakly transversely isotropic soft tissues within less than 20 ms of acquisition for the entire imaged volume.

Evaluation of site effects on ground motions based on equivalent linear site response analysis and liquefaction potential in Chennai, south India

We study local site effects with detailed geotechnical and geophysical site characterization to evaluate the site-specific seismic hazard for the seismic microzonation of the Chennai city in South India. A Maximum Credible Earthquake (MCE) of magnitude 6.0 is considered based on the available seismotectonic and geological information of the study area. We synthesized strong ground motion records for this target event using stochastic finite-fault technique, based on a dynamic corner frequency approach, at different sites in the city, with the model parameters for the source, site, and path (attenuation) most appropriately selected for this region. We tested the influence of several model parameters on the characteristics of ground motion through simulations and found that stress drop largely influences both the amplitude and frequency of ground motion. To minimize its influence, we estimated stress drop after finite bandwidth correction, as expected from an M6 earthquake in Indian peninsula shield for accurately predicting the level of ground motion. Estimates of shear wave velocity averaged over the top 30 m of soil (VS30) are obtained from multichannel analysis of surface wave (MASW) at 210 sites at depths of 30 to 60 m below the ground surface. Using these VS30 values, along with the available geotechnical information and synthetic ground motion database obtained, equivalent linear one-dimensional site response analysis that approximates the nonlinear soil behavior within the linear analysis framework was performed using the computer program SHAKE2000. Fundamental natural frequency, Peak Ground Acceleration (PGA) at surface and rock levels, response spectrum at surface level for different damping coefficients, and amplification factors are presented at different sites of the city. Liquefaction study was done based on the VS30 and PGA values obtained. The major findings suggest show that the northeast part of the city is characterized by (i) low VS30 values (< 200 m/s) associated with alluvial deposits, (ii) relatively high PGA value, at the surface, of about 0.24 g, and (iii) factor of safety and liquefaction below unity at three sites (no. 12, no. 37, and no. 70). Thus, this part of the city is expected to experience damage for the expected M6 target event.

Rotational motions from the 2016, Central Italy seismic sequence, as observed by an underground ring laser gyroscope

We present the analysis of rotational and translational ground motions from earthquakes recorded during October-November 2016, in association with the Central Italy seismic sequence. We use co-located measurements of the vertical ground rotation rate from a large ring laser gyroscope and the three components of ground velocity from a broad-band seismometer. Both instruments are positioned in a deep underground environment, within the Gran Sasso National Laboratories of the Istituto Nazionale di Fisica Nucleare. We collected dozens of events spanning the 3.5-5.9 magnitude range and epicentral distances between 30 and 70 km. This data set constitutes an unprecedented observation of the vertical rotational motions associated with an intense seismic sequence at local distance. Under the plane-wave approximation we process the data set in order to get an experimental estimation of the events backazimuth. Peak values of rotation rate (PRR) and horizontal acceleration (PGA) are markedly correlated, according to a scaling constant which is consistent with previous measurements from different earthquake sequences. We used a prediction model in use for Italy to calculate the expected PGA at the recording site, obtaining consequently predictions for PRR. Within the modelling uncertainties, predicted rotations are consistent with the observed ones, suggesting the possibility of establishing specific attenuation models for ground rotations, like the scaling of peak velocity and peak acceleration in empirical ground-motion prediction relationships. In a second step, after identifying the direction of the incoming wavefield, we extract phase-velocity data using the spectral ratio of the translational and rotational components. This analysis is performed over time windows associated with the P-coda, S-coda and Lg phase. Results are consistent with independent estimates of shear wave velocities in the shallow crust of the Central Apennines.

Site Classification using Multichannel Channel Analysis of Surface Wave (MASW) method on Soft and Hard Ground

Site classification utilizing average shear wave velocity (Vs(30) up to 30 meters depth is a typical parameter. Numerous geophysical methods have been proposed for estimation of shear wave velocity by utilizing assortment of testing configuration, processing method, and inversion algorithm. Multichannel Analysis of Surface Wave (MASW) method is been rehearsed by numerous specialist and professional to geotechnical engineering for local site characterization and classification. This study aims to determine the site classification on soft and hard ground using MASW method. The subsurface classification was made utilizing National Earthquake Hazards Reduction Program (NERHP) and international Building Code (IBC) classification. Two sites are chosen to acquire the shear wave velocity which is in the state of Pulau Pinang for soft soil and Perlis for hard rock. Results recommend that MASW technique can be utilized to spatially calculate the distribution of shear wave velocity (Vs(30)) in soil and rock to characterize areas.

Near-surface shear wave velocity estimation and V s 30 mapping for Dhaka City, Bangladesh

Dhaka, the capital city of Bangladesh, is one of the seismically vulnerable cities in the world due to its location close to the convergent boundary between the Eurasian and Indian Plates, unplanned urbanization, non-engineered construction practice, high population density, and weak emergency response system. The city is developed on an elevated Pleistocene terrace with surrounding Holocene floodplains. The terrace consists of the Pleistocene clayey soils, and the floodplains are composed of alluvial sandy and clayey soils. The average shear wave velocity of the near-surface soils up to a depth of 30 m (V s 30 ) is required for Dhaka City to estimate the amplification factors of seismic waves for site-specific seismic hazard analysis. Therefore, the V s 30 has been estimated in the city using downhole seismic (DS), multichannel analysis of surface waves (MASW), and small-scale microtremor measurement (SSMM) methods, and empirical correlation between the shear wave velocity (Vs) and standard penetration test blow count (SPT-N). The V s 30 has also been predicted using the relationship between the V s 30 and Holocene soil thickness. The V s 30 results of the DS, MASW, SSMM, and SPT-N vary from 127 to 320 m/s. The V s 30 values that are predicted based on the Holocene soil thickness vary from 145 to 260 m/s. Then, a V s 30 map has been prepared for Dhaka City using the V s 30 values that are predicted from the Holocene soil thickness at a grid of 30 m. The near-surface soils of the city are classified based on the V s 30 as site classes D (stiff soils) and E (soft soils) according to the NEHRP (National Earthquake Hazards Reduction Program, the USA) and as subsoil classes C and D according to the Eurocode 8.

Discussion on “Shear wave velocity and soil type microzonation using neural networks and geographic information system” [Soil Dyn Earthq Eng 104 (2018) 54–63

The article studied by M.M. Nejad, M.S. Momeni and K.N. Manahiloh (Soil Dynamics and Earthquake Engineering, 104, 2008, 54–63) needs some clarifications regarding the use of the Neural Network (NN) approach with Geographic Information System (GIS) for microzonation. The NN effort with the integration of GIS in the study is not a function approximation problem, thus it can not estimate shear wave velocity (Vs), as well as site classification. This discussion aims to present some controversial points of the article for the use of NN integrated with GIS for microzonation.

Tool for analysis of multichannel analysis of surface waves (MASW) field data and evaluation of shear wave velocity profiles of soils

Multichannel analysis of surface waves (MASW) is a fast, low-cost, and environmentally friendly technique to estimate shear wave velocity profiles of soil sites. This paper introduces a new open-source software, MASWaves, for processing and analysing multichannel surface wave records using the MASW method. The software consists of two main parts: a dispersion analysis tool (MASWaves Dispersion) and an inversion analysis tool (MASWaves Inversion). The performance of the dispersion analysis tool is validated by comparison with results obtained by the Geopsy software package. Verification of the inversion analysis tool is carried out by comparison with results obtained by the software WinSASW and theoretical dispersion curves presented in the literature. Results of MASW field tests conducted at three sites in south Iceland are presented to demonstrate the performance and robustness of the new software. The soils at the three test sites ranged from loose sand to cemented silty sand. In addition, at one site, the results of existing spectral analysis of surface waves (SASW) measurements were compared with the results obtained by MASWaves.

Seismic Site Classification and Liquefaction Hazard Assessment of Jaipur City, India

Multichannel Analysis of Surface Wave (MASW) is one of the latest geophysical methods used for determining the shear wave velocity of the soil. A series of MASW tests were carried out in this study using a multi channel seismograph with 24 numbers of 4.5 Hz vertical geophones. Collected data were analysed using Surface Plus software. One-dimensional shear wave velocity models were developed from the analyses of the collected data for the Jaipur city. The average shear wave velocity (VS30) for the top 30 m of soil deposit was estimated for the Jaipur city. Based on this VS30 value, the Jaipur city was finally divided into various sub-zones as per the NEHRP guidelines. From the study it has been observed that all the studied areas are falling either in site class C or D. In top 15 m depth, almost all studied area is having average shear wave velocity less than 360 m/s. The estimated shear wave velocity data were used in the assessment of liquefaction potential of soil at various locations in the city. From the liquefaction potential results it can be concluded that most of the city area is not susceptible to liquefaction.

Random-effects regression model for shear wave velocity as a function of standard penetration test resistance, vertical effective stress, fines content, and plasticity index

A random effect regression model is used to formulate a unified equation and estimate shear wave velocity (Vs). Standard penetration test (SPT) number, effective overburden pressure, plasticity index, and the fines content (Fc) are used as input parameters. First, a fixed model regression is used to obtain the regression parameters. SPT number and shear wave velocity are measured at 2m intervals up to a depth of 10m, for 71 boreholes, distributed evenly in Urmia city. Plasticity index and fines content are evaluated from laboratory tests that were performed on 355 samples obtained from the 71 boreholes (i.e., 5 samples from each borehole). Statistical analysis performed on the fixed effect model showed the need for examining the random effects arising from variable SPT test conditions in each borehole. A mixed effect regression model is employed to investigate such effects. The distribution of residuals is found to satisfy the normality criteria for the mixed effect model. A strong fit for the model is obtained, and through statistical evidence, it is implied that the proposed model is practical. The model's most prominent feature is the capability of unifying different soil types via the incorporation of plasticity index and fines content as inputs.

Role of acoustic radiation force impulse and shear wave velocity in prediction of preterm birth: a prospective study.

Background Preterm birth is one of the important causes of neonatal morbidity where we rely on subjective criteria such as modified Bishop's scoring and contemporary sonographic measurement of cervical length. Acoustic radiation force impulse (ARFI) is a technological advancement in elastography that can be employed in prediction of cervical softening and preterm labor. Purpose To evaluate the role of ARFI technique and shear wave velocity (SWV) estimates as a predictor of preterm birth and its comparison with other clinical and sono-elastographic measures. Material and Methods Thirty-four pregnant women (gestation age = 28-37 weeks age) showing features suggestive of preterm labor were included and evaluated with modified Bishop's score, cervical length by ultrasound (US), ARFI to derive Elastography index (EI), and SWV of the cervix. The patients were later divided into two groups, using the clinical outcome of preterm or term delivery. Results Twenty patients delivered at term (gestational age > 37 weeks) and 14 were preterm. Receiver operating characteristics (ROC) curves showed SWV with highest sensitivity and specificity (93% and 90%, respectively) for the prediction of preterm birth at a cutoff value of 2.83 m/s. EI and modified Bishop's score were comparable to each other, but were less sensitive techniques. Conclusion Elastographic assessment of antenatal cervix is a novel technique of virtual palpation of internal os and can be utilized as an objective criterion for preterm birth prediction.