S-wave Velocity Profiles Research Articles

S-wave velocity structure and site effect parameters derived from microtremor arrays in the Western Plain of Taiwan

In this study, microtremor array measurements were conducted at 45 sites in the Western Plain of Taiwan. The arrays were approximately 30m or 60m in radius, depending on the site. The maximum-likelihood frequency–wavenumber method was adopted to obtain the phase velocities of Rayleigh waves, and then a genetic algorithm technique based on an inversion scheme of the fundamental mode of the Rayleigh waves’ dispersion curves was applied to calculate a preliminary S-wave velocity (Vs) profile at each site. Because a layer of thick sediment covers the bedrock in the Western Plain of Taiwan, microtremor arrays in this size range cannot estimate the structure of the entire sediment. Therefore, this study implemented further inversion of the horizontal-to-vertical spectral ratios of the microtremors to estimate the deeper structures up to the bedrock of Vs greater than 1000m/s. Previously logged velocity profiles for different depths at or near our study sites were collected and compared with the Vs profiles derived from our microtremor array measurements; the results were found to be highly comparable. Therefore, we could delineate the depth distributions for the layer depths for Vs=600m/s and 1000m/s in this region. The depth for Vs=600m/s is approximately 50m in the piedmont area and approximately 300m at the coastline; moreover, the depths for Vs=1000m/s increase from 200m in the piedmont area to approximately 1000m at the coastline. The depths for Vs=1.0km/s (Z1.0), which is an important parameter that accounts for the basin effect in recent ground motion prediction equations, are consequently available at the study sites. The distribution of Z1.0 as a function of Vs30 indicates higher similarity to that in Japan than in the San Francisco Bay area.

Estimation of site effects using strong motion data of BYTNet array in Turkey

Simultaneous estimation of effects of source, propagation path, and local site amplification was carried out using observed strong motion records in a frequency range from 0.8 to 20 Hz for the purpose of empirical evaluation of the local site effects in different geological conditions in the northwestern part of Turkey. The analyzed data are S-wave portions of 162 accelerograms from 39 shallow events observed at 14 sites of BYTNet array. A spectral separation method was applied to the observed S-wave spectra. The solutions for source spectra, inelasticity factor of propagation path for S-waves (Q s-value), and factor of site amplification at each site were obtained in a least squares sense. In the analysis, we assumed that the factor of the site amplification at a reference site is the same as that of theoretical amplification of S-waves to the soil model whose bottom layer has an S-wave velocity around 2.15 km/s. The estimated Q s-value of the propagation path is modeled as Q s(f) = 87.4f0.78. The estimated site amplifications are characterized into three groups. The sites in the first group belong to rock site with no dominant peaks at a frequency range of 2 to 10 Hz. The second group of hard soil sites is characterized with moderately dominant peaks at a frequency of 5 Hz. The last group for soft soil sites has common peaks at a frequency of 4 Hz with larger amplitudes than those in the hard soil group. We, then, compare the amplifications with average S-wave velocity in top 30 m of the shallow S-wave profiles and proposed linear empirical formula between them at each frequency. We, furthermore, inverted the observed amplification factors into S-wave velocity and Q s-value profiles of the deep soil over the basement.

P- and S-wave velocity models of shallow dry sand formations from surface wave multimodal inversion

Surficial formations composed of loose, dry granular materials constitute a challenging target for seismic characterization. They exhibit a peculiar seismic behavior, characterized by a nonlinear seismic velocity gradient with depth that follows a power-law relationship, which is a function of the effective stress. The P- and S-wave velocity profiles are then characterized by a power-law trend, and they can be defined by two power-law exponents [Formula: see text] and two power-law coefficients [Formula: see text]. In case of depth-independent Poisson’s ratio, the P-wave velocity profile can be defined using the [Formula: see text] power-law parameters and Poisson’s ratio. Because body wave investigation techniques (e.g., P-wave tomography) may perform ineffectively on such materials because of high attenuation, we addressed the potential of surface-wave method for a reliable seismic characterization of shallow formations of dry, uncompacted granular materials. We took into account the dependence of seismic wave velocity on effective pressure and performed a multimodal inversion of surface-wave data, which allowed the [Formula: see text] and [Formula: see text] profiles to be retrieved. The method requires the selection of multimodal dispersion curve points referring to surface-wave frequency components traveling within the granular media formation and their inversion for the S-wave power-law parameters and Poisson’s ratio. We have tested our method on a synthetic dispersion curve and applied it to a real data set. In both cases, the surficial layer was made of loose dry sand. The test on the synthetic data set confirmed the reliability of the proposed procedure because the thickness and the [Formula: see text], [Formula: see text] profiles of the sand layer were correctly estimated. For the real data, the outcomes were validated by other geophysical measurements conducted at the same site and they were in agreement with similar studies regarding loose sand formations.

Layered internal structure and breaching risk assessment of the Higashi-Takezawa landslide dam in Niigata, Japan

The internal structure and geotechnical properties of landslide dams have rarely been examined in detail, although they largely control the longevity and potential failure mechanisms of the dams. During the 2004 Mid-Niigata Prefecture earthquake, thousands of landslides were triggered and many landslide dams were formed in the Imo River basin. Among these landslides dams, the biggest one that occurred in the Higashi-Takezawa district threatened both the upstream and downstream areas. Emergency and eventual permanent countermeasures were successfully performed to mitigate the hazards presented by the dam. The preserved landslide dam provides a good field study area for improving understanding of the formation and stability of similar features. To characterize its internal structure and to provide more reliable information for stability analysis, we used a multiple-channel surface-wave technique and microtremor array measurements to survey the dam's S-wave velocity (Vs) profile. Our results show that the integrated use of these methods is an effective approach for determining the S-wave velocity structure of landslide dams, irrespective of the mountainous environment in which they typically occur. The Vs profile suggests that the displaced landslide materials had been little disturbed during movement, although movement was rapid and over a long distance. We also discuss herein the landsliding mechanism and assess the breaching risk of the landslide dam due to overtopping.

Three-dimensional P- and S-wave velocity profiling of geotechnical sites using full-waveform inversion driven by field data

We discuss the application of a recently developed full-waveform-inversion-based technique to the imaging of geotechnical sites using field-collected data. Specifically, we address the profiling of arbitrarily heterogeneous sites in terms of P- and S-wave velocities in three dimensions, using elastic waves as probing agents. We cast the problem of finding the spacial distribution of the elastic soil properties as an inverse medium problem, directly in the time domain, and use perfectly-matched-layers (PMLs) to account for the semi-infinite extent of the site under investigation.After briefly reviewing the theoretical and computational aspects of the employed technique, we focus on the characterization of the George E. Brown Jr. Network for Earthquake Engineering Simulation site in Garner Valley, California (NEES@UCSB). We compare the profiles obtained from our full-waveform-inversion-based methodology against the profiling obtained from the Spectral-Analysis-of-Surface-Waves (SASW) method, and report agreement. In an attempt to validate our methodology, we also compare the recorded field data at select control sensors that were not used for the full-waveform inversion, against the response at the same sensors, computed based on the full-waveform-inverted profiles. We report very good agreement at the control sensors, which is a strong indicator of the correctness of the inverted profiles. Overall, the systematic framework discussed herein seems robust, general, practical, and promising for three-dimensional site characterization purposes.

Testing the reference Moon model in respect of the thermal regime and chemical composition of the mantle: Thermodynamics versus seismology

The VPREMOON seismic reference Moon model (Garcia et al., 2011) has been tested with respect to the thermal regime and chemical composition of the mantle. Based on a self-consistent thermodynamic approach and petrological models of the lunar mantle covering a wide range of concentrations of CaO, Al2O3, and FeO, we convert the P- and S-wave velocity profiles to the temperature–depth profiles. The solution procedure relies on the method of the Gibbs free energy minimization and the equations of state for the mantle material which take into account the effects of phase transformations, anharmonicity, and anelasticity. We find that regardless of the chemical composition, the positive P- and S-wave velocity gradient in the lunar mantle leads to a negative temperature gradient, which has no physical basis. For adequate mantle temperatures, the P- and S-wave velocities should remain almost constant or slightly decrease with depth (especially V S ) as a result of the effects of the temperature, which grows faster than pressure. These findings underscore the importance of the relationship of the thermodynamics and physics of minerals with seismology.

Subsurface Shear Wave Velocity Characterization Using P-Wave Seismograms in Central and Eastern North America

The time-averaged shear ( S) wave velocity in the upper 30 meters of sediment ( V S30) is a widely used site parameter for ground motion prediction. When unavailable from measurements, as is often the case at accelerograph stations in Central and Eastern North America (CENA), V S30 is typically estimated from proxies. We propose an alternative for CENA based on a theoretical relationship between S-wave velocity and the ratio of radial to vertical components of the compressional ( P)-wave–dominated portion of the velocity time series. This method is applied to 31 CENA accelerograph sites having measured S-wave velocity profiles. Time-averaged S-wave velocities to depth z ( V SZ) from the proposed method agree well with those from measurements. We develop linear relationships between V SZ and V S30 using CENA S-wave velocity profile data. Values of V S30 established from the proposed method (including depth extrapolation) have lower dispersion relative to data ( σln V = 0.43) than do estimates from available CENA proxies.

The lithosphere, LAB, LVZ and Lehmann discontinuity under central Fennoscandia from receiver functions

P- and S-wave velocity profiles (Vp and Vs) from the Earth's surface to a depth of 300km are obtained by simultaneous inversion of P- and S-wave receiver functions for the temporary POLENET/LAPNET array in northern Finland and 5 permanent stations in southern Finland. The obtained Vp/Vs velocity ratio in the uppermost mantle is anomalously low (1.65–1.70 versus the standard 1.8). This ratio can be explained by a high (~30%) fraction of orthopyroxene in the depleted upper mantle. An increase of ~4% in the Vs values is detected at a depth of 110–130km. Under southern Finland the high-velocity mantle keel may extend beyond the depth of 300km, but under northern Finland we detect a low-Vs zone (LVZ) with the top at a depth of 160km. This depth corresponds to the intersection of the geotherm with the wet solidus of peridotite at a temperature near ~1100°C, and suggests partial melting as an explanation for the origin of the LVZ. The bottom of the LVZ (the Lehmann discontinuity) is found at a depth of 240km. The fast direction of seismic azimuthal anisotropy beneath northern Finland in the depth interval from 200–240km to 320km is parallel to the current APM direction (60°) but in the interval from 160km to 200–240km the fast direction (150°) appears to be normal to the APM direction (Vinnik et al., 2014). The present study indicates that the fast direction of 150° confines to the LVZ where the flow in the direction normal to the APM direction is unlikely. More likely, the flow direction is parallel to the APM direction and normal to the fast direction of anisotropy, as suggested by experiments with sheared peridotite-type rocks containing melt.

Predictive equations for soil shear-wave velocities of Hungarian soils based on MASW and CPT measurements around Győr

Determination of shear-wave (S-wave) velocity profiles is the first step in seismic hazard assessment of a town, because the dynamic parameters of local soil types are vital for seismic response analysis of a specific area in order to determine the local soil effect in a case of a seismic event for seismic risk analysis. S-wave velocity profiles have been determined for many areas within Győr. Extensive use of historical boring logs allowed for correlations and reasonable extrapolation of soil performance throughout the area. This has led to a pattern of soil layer distributions and delineates several different soil zones for Győr.

Estimation of surface-wave phase velocity from microtremor observation using an array with a reference station

A procedure for estimation of Rayleigh wave phase velocities from microtremor observations, using an array with a reference station, is investigated in this study. Simultaneous observation of microtremors at a reference station and at a strong motion observation array in the Kanto Basin, Japan, was carried out. We first calculated cross correlations between records at the reference station and those at stations in the array using a seismic interferometric processing method on a 4300-h data series. After identifying dispersive Rayleigh waves from results of multiple filtering analysis of the cross correlations, semblance analysis of the cross correlations for different segments was carried out to estimate phase velocities for fundamental and higher-mode Rayleigh waves. The phase velocities from the proposed method are more appropriate than those from conventional methods at long periods as they avoid contamination by higher mode Rayleigh waves. The fundamental Rayleigh wave phase velocities were inverted to an S-wave velocity profile for deep sedimentary layers.We also examined the variations in the phase velocity with decreasing data duration. The phase velocities at periods less than 3 s from 6-h records are similar to those from 4300-h records, suggesting that our method is possibly applicable in microtremor exploration.

Exploration of deep sedimentary layers in Tacna city, southern Peru, using microtremors and earthquake data for estimation of local amplification

S-wave velocity profiles of sedimentary layers in Tacna, southern Peru, based on analysis of microtremor array data and earthquake records, have been determined for estimation of site amplification. We investigated vertical component of microtremors in temporary arrays at two sites in the city for Rayleigh wave phase velocity. A receiver function was also estimated from existing earthquake data at a strong motion station near one of the microtremor exploration sites. The phase velocity and the receiver function were jointly inverted to S-wave velocity profiles. The depths to the basement with an S-wave velocity of 2.8 km/s at the two sites are similar as about 1 km. The top soil at the site in a severely damaged area in the city had a lower S-wave velocity than that in a slightly damaged area during the 2001 southern Peru earthquake. We subsequently estimate site amplifications from the velocity profiles and find that amplification is large at periods from 0.2 to 0.8 s at the damaged area indicating possible reasons for the differences in the damage observed during the 2001 southern Peru earthquake.

Characterization of the geological and geotechnical properties of soil using the surface wave approach

<p>As part of the efforts to examine the elastic and engineering properties of the subsurface sequence at a proposed new power plant site in Edo State, a geophysical survey involving Multichannel Analysis of Surface Waves (MASW) was carried out. The MASW was adopted to determine the vertical and lateral variations in velocity beneath each seismic line. The MASW was carried out on two seismic lines each trending NE-SW. A geophone interval of 3 m was used, and the length of the seismic lines ranged from 60 – 90 m. The ES-3000 seismograph was used for the surface wave data acquisition and the Shear-Wave velocity structures of the area were obtained through the inversion of the acquired surface wave data. The one dimensional (1D) S-Wave velocity profiles along the lines were diagnostic of generally low velocity lithologies that suggest sand, clayey sand and sandy clay formations with relatively varying thicknesses. The subsurface layers delineated had shear-wave velocity values in the range of 63-400 m/s. They were classified using the NEHRP Seismic Site Classification, and all of them were in the range of stiff soil to soft clay soil. The bulk moduli (k) for these soils were in the range of 3.22-3.98 GPa. This depicts relatively low strength of the subsurface materials. The shear moduli (μ) values range from 7.15-7.43 MPa, which is indicative of low to moderate strength. The information provided in this study will aid the structural engineer or architect in foundation design of the proposed power plant. From the results of this study, it is concluded that although the subsurface layers are of relatively low strength, with the right intervention of the civil engineer, a suitable foundation can be designed for the gas plant.</p>

Application of artificial bee colony algorithm on surface wave data

Artificial bee colony (ABC) algorithm is applied to invert surface wave phase velocities. The ABC algorithm, one of swarm intelligence-based algorithms, is inspired from the particular intelligent foraging behavior of a honeybee swarm in nature. To facilitate convergence to an optimal solution, global exploration and local exploitation processes are carried out simultaneously in a robust ABC search process. Using synthetic and observed Rayleigh wave data, we examined the effectiveness and applicability of the ABC scheme in deducing an S-wave velocity profile for near-surface applications. Furthermore, we compared the performance of ABC to those of genetic algorithm (GA) and particle swarm optimization (PSO). We demonstrated that the ABC algorithm outperforms the standard binary-coded GA and the basic PSO, and it can be effectively used to interpret surface wave dispersion data with the great advantage of employing fewer control parameters.

Soil characteristics in Doon Valley (north west Himalaya, India) by inversion of H/V spectral ratios from ambient noise measurements

Past and recent observations have shown that the local site conditions significantly affect the behavior of seismic waves and its potential to cause destructive earthquakes. Thus, seismic microzonation studies have become crucial for seismic hazard assessment, providing local soil characteristics that can help to evaluate the possible seismic effects. Among the different methods used for estimating the soil characteristics, the ones based on ambient noise measurements, such as the H/V technique, become a cheap, non-invasive and successful way for evaluating the soil properties along a studied area.In this work, ambient noise measurements were taken at 240 sites around the Doon Valley, India, in order to characterize the sediment deposits. First, the H/V analysis has been carried out to estimate the resonant frequencies along the valley. Subsequently, some of this H/V results have been inverted, using the neighborhood algorithm and the available geotechnical information, in order to provide an estimation of the S-wave velocity profiles at the studied sites.Using all these information, we have characterized the sedimentary deposits in different areas of the Doon Valley, providing the resonant frequency, the soil thickness, the mean S-wave velocity of the sediments, and the mean S-wave velocity in the uppermost 30m.

Backtracking search algorithm for effective and efficient surface wave analysis

Surface wave dispersion analysis is widely used in geophysics to infer near-surface shear (S)-wave velocity profiles for a wide variety of applications. However, inversion of surface wave data is challenging for most local-search methods due to its high nonlinearity and to its multimodality. In this work, we proposed and implemented a new Rayleigh wave dispersion curve inversion scheme based on backtracking search algorithm (BSA), a novel and powerful evolutionary algorithm (EA). Development of BSA is motivated by studies that attempt to develop an algorithm that possesses desirable features for different optimization problems which include the ability to reach a problem's global minimum more quickly and successfully with a small number of control parameters and low computational cost, as well as robustness and ease of application to different problem models.The proposed inverse procedure is applied to nonlinear inversion of fundamental-mode Rayleigh wave dispersion curves for near-surface S-wave velocity profiles. To evaluate calculation efficiency and effectiveness of BSA, four noise-free and four noisy synthetic data sets are firstly inverted. Then, the performance of BSA is compared with that of genetic algorithms (GA) by two noise-free synthetic data sets. Finally, a real-world example from a waste disposal site in NE Italy is inverted to examine the applicability and robustness of the proposed approach on real surface wave data. Furthermore, the performance of BSA is compared against that of GA by real data to further evaluate scores of BSA.Results from both synthetic and actual data demonstrate that BSA applied to nonlinear inversion of surface wave data should be considered good not only in terms of the accuracy but also in terms of the convergence speed. The great advantages of BSA are that the algorithm is simple, robust and easy to implement. Also there are fewer control parameters to tune.

Estimation of S-wave Velocity Structure for Sedimentary Layered Media Using Microtremor Array Measurements in Palu City, Indonesia

In this study, 8 array microtremor measurements have performed in Palu City, Indonesia for S-wave velocity profiles, which will be used in seismic hazard mapping. Four accelerometers were used in each array observation site. One was installed at a center of the circle with a radius, r. Other three were arranged on the circle with a shape of regular triangle. Sequential observations were conducted three times by changing the array radius; r=3, 10 and 30 meters. The ground profile was estimated by means of the dispersion curves obtained using the Spatial Autocorrelation (SPAC) methods. The Particle Swarm Optimization (PSO) technique was introduced to determine the dispersion curves. Unified two-layered model were reconstructed by averaging the first three layers obtained from array observation. The shear wave velocity of the top layer is Vs≤ 300 m/s. Based on layer models identified, sedimentary layer was estimated around Palu City.Understanding the parameters of sedimentary layersis important for seismic hazard mitigation and environmental planning in Paul City.

Identification of Engineering Bedrock in Jakarta by Using Array Observations of Microtremors

The bedrock depth is one of the most important parameters in seismic hazard analysis. This parameter has not been identified well in Jakarta. This study was conducted to determine the bedrock depth in Jakarta based on S-wave velocity parameters. Microtremors array method was applied in this study to obtain 1D and 2D S-wave velocity profiles. The spatial autocorrelation (SPAC) method was used to estimate dispersion curves, while S-wave velocity structure was derived by genetic algorithm. Reffering to the geological condition in the study area, microtremors array measurements were conducted for two East-West lines in the northern and southern parts of Jakarta. The result of 2D construction of S-wave velocity structure shows stratigraphy cross sections that consists of four layers, where the bedrock depths in northern Jakarta can be depicted in the range from 519 to 662 m and in the southern part in the range from 353 m to 399 m. It has a positive correlation with the local geological condition i.e the sediment thickness increases to the north.

Estimation of S-Wave Velocity Profiles at Lima City, Peru Using Microtremor Arrays

Microtremor exploration was performed around seismic recording stations at five sites in Lima city, Peru in order to know the site amplification at these sites. The Spatial Autocorrelation (SPAC) method was applied to determine the observed phase velocity dispersion curve, which was subsequently inverted in order to estimate the 1-D S-wave velocity structure. From these results, the theoretical amplification factor was calculated to evaluate the site effect at each site. S-wave velocity profiles at alluvial gravel sites have S-wave velocities ranging from ∼500 to ∼1500 m/s which gradually increase with depth, while Vs profiles at sites located on fine alluvial material such as sand and silt have Swave velocities that vary between ∼200 and ∼500 m/s. The site responses of all Vs profiles show relatively high amplification levels at frequencies larger than 3 Hz. The average transfer function was calculated to make a comparison with values within the existing amplification map of Lima city. These calculations agreed with the proposed site amplification ranges.

S-wave cross-hole logging for stone columns

S-wave cross-hole logging was successfully developed to outline the shape of a stone column and to confirm in turn its integrity. The technique is, in conception, quite identical to the Cross-hole Sonic Logging (CSL) for drilled piers. One of the key distinctions is the use of s-wave, which can be conveniently measured using the s-wave logger developed by the authors. The other key feature is that the s-wave velocity profile of the aggregates (Va profile) is required to back-calculate the diameters of the column. Va profile can be evaluated with the internal friction angle and the coefficient of earth pressure at rest of the aggregates. Fortunately, the calculation of the diameters is inherently very rugged against the uncertainty of Va profile. The technique can even detect bottle-neck and gourd-shaped anomalies of the stone column.

Development of a Seismic Microzoning Map for Lima City and Callao, Peru

The location of Lima city and El Callao in the Pacific coast and the long history of seismic activity were the main reasons to develop a seismic microzoning map. The microzoning study was based on large numbers of geotechnical and geophysical exploration points distributed around the study area. The geotechnical exploration consisted of borehole tests and pits, from which soil samples were taken to the laboratory to determine the soil mechanical characteristics. The geophysical exploration consisted of onepoint microtremor measurements and various methods to estimate the S-wave velocity profile. The results of both, the geotechnical and geophysical exploration were combined to develop a seismic microzoning map for Lima city and El Callao. This map shows five zones, where the zone with the best soil mechanical and dynamic characteristics covers most of the study area.