Multichannel Analyzer Research Articles

Seismic site characterization using MASW and correlation study between shear wave velocity and SPT[sbnd

A seismic site characterization study is carried out in the south of the foothills of tectonically active Himalayan region. During an earthquake, the dynamic characteristics of the shallow subsurface strata can influence seismic shaking in the region, causing damage to civil infrastructures. The seismic site characterization study with shear wave velocity (Vs) is performed using the Multi-channel Analysis of Surface Wave (MASW) technique, which is particularly challenging to implement in the densely inhabited areas. However, the standard penetration test (SPTN) commonly measured by civil engineers can be utilized to compute Vs of such areas by establishing a correlation between Vs and the SPT-N values.In the study area, MASW data were acquired at twelve different locations, whereas SPT-N tests were available from 26 boreholes. Twelve borehole locations closer to the MASW survey lines were paired to establish relationships between SPT-N and Vs. The developed linear and non-linear correlation functions were found to be statistically similar. Furthermore, the linear correlation function is used for estimating Vs from SPT-N in remaining 14 boreholes. The new correlation functions were further compared with previously reported empirical relationships from other areas. The current relationship can be used for geoengineering purposes at different sites with similar geological conditions.Shear wave velocity derived from the MASW surveys and estimated from the new empirical relationship was utilized for seismic site characterization based on average shear wave velocity up to 30 m depth (Vs30). The Vs30 map of the study site is prepared and classified in accordance with the National Earthquake Hazard Reduction Program (NEHRP-2020). The calculated Vs30 value of the study site ranges from 285 to 375 m/s. The major portion of the study area lies under Site Class CD, with a minor portion under Site Class D. In the event of an earthquake, some zones can potentially have stronger ground amplification, particularly in Site Class D and may have damaging effects. A series of average shear wave velocity maps for different depths are prepared to help geotechnical engineers in identifying and mitigating geotechnical risks. Furthermore, there are potential geohazard risks as certain depths show low shear velocity.

Do Working and Parenting Trajectories Influence Retirement Timing? Evidence From Spain, Using a Sequence Analysis Approach and Focusing on Women

Abstract This paper investigates the association between accumulated experiences in the working and parenting spheres and retirement timing among Spanish women, utilizing data from the Survey of Health, Ageing and Retirement in Europe (SHARE). The study examines whether labor market attachment or cumulative disadvantage characterizes women’s retirement and how these factors relate with the number of children. Firstly, multichannel sequence analysis and cluster analysis were employed to identify distinct work–family life courses from ages 20 to 50. Seven clusters were identified: “Full-time work with 2+ children,” “Out of the labour force and 2+ children,” “Mid-life discontinuity and 2+ children,” “Full-time work and 1 child,” “Full-time work and childless,” “Part-time work and 2+ children,” and “Part-time work or out of the labor force and 1 child.” Secondly, the study examines the association between these identified groups and retirement timing. The results indicate that Spanish women who have experienced more unstable careers characterized by extended periods of inactivity or part-time work, particularly in combination with having 2 or more children, are more likely to retire at a later age compared with women with continuous careers, with or without children. These findings underscore the ongoing challenges of balancing unpaid care work and wage work in Spain, while also revealing notable variations among women.

Multi-channel frequency difference noise analysis and cancellation method for the balanced field electromagnetic pipeline inspection gauge.

The balanced field electromagnetic technique as an effective in-line inspection method for cracks in long-distance oil and gas pipelines uses the pipeline inspection gauge (PIG) as the detection tool. PIG is characterized by the employment of a large number of sensors, but as each channel uses its crystal oscillator as a signal source, it inevitably generates frequency difference noise, which affects crack detection. A method of eliminating the frequency difference noise by using same-frequency excitation is proposed to solve the problem. Combining the principle of electromagnetic field propagation with the detection signal processing process, the formation process and characteristics of the frequency difference noise are theoretically analyzed, and the specific impact of frequency difference noise on crack detection is analyzed. The method of unified clock excitation for all channels is adopted, and a same-frequency excitation system is developed. The correctness of the theoretical analysis and the validity of the proposed method are verified by platform experiments and pulling tests. The results show that the effect of the frequency difference on noise follows the whole detection process, and the smaller the frequency difference, the longer the noise period. The frequency difference noise distorts the crack signal and is of comparable magnitude to the crack signal, which tends to drown out the crack signal. The same-frequency excitation method can eliminate frequency difference noise at the source and has a high signal-to-noise ratio. The method can provide a reference for multi-channel frequency difference noise cancellation in other AC detection technologies.

An inversion method for evaluating ballastless track degradation based on multi-channel analysis of surface wave

Due to the heterogeneous properties of constituent materials, traditional Multi-channel analysis of surface wave (MASW) method is unsuitable for evaluating ballastless track as surface waves exhibit different dispersion patterns. To overcome this limitation, firstly, the implementation process of MASW was introduced, and the phase shift method was employed to perform dispersion analysis of multi-channel surface wave signals. Secondly, a wave field solution model of ballastless track was established using the time-domain finite-difference method. Subsequently, the stiffness matrix method was improved to account for the heterogeneous properties of the constituent materials and to calculate the theoretical surface wave dispersion curve of ballastless track, followed by the analysis of surface wave dispersion characteristics in ballastless track and the proposal of an inversion method. Finally, the optimal excitation central frequency and receivers’ deployment were analyzed in the MASW method, and the inversion analysis of ballastless track degradation were conducted. Results shown that the surface wave dispersion curve is more sensitive to CA mortar degradation at low frequencies and concrete slab degradation at high frequencies. Appropriate excitation central frequency and receivers’ deployment are essential for accurately extracting the surface wave dispersion curve from the dispersion energy of ballastless tracks. The inversion method proposed in this study provides a more accurate evaluation of ballastless track degradation compared to assuming ballastless track as a homogeneous structure during inversion analysis.

Investigation of a Beta Spectrum through Virtual MCA Supported By Virtual Oscilloscope

In this study, the performance of a developed virtual MCA (Multichannel Analyzer) was tested in a beta spectrometer. A real MCA was also used in the spectrometer to compare the results from the virtual one. The beta energy spectrum of a 204Tl radioactive source was displayed in the real and virtual MCAs. Total counts in the spectra from both MCAs were determined for different data acquisition times. In addition to the total counts, spectrum shapes, starting and ending channel numbers of the beta spectrum from the virtual MCA were also compared with those of the real one. Besides, an oscilloscope feature was brought in to the virtual MCA different from the conventional ones. The output signal shapes of a main amplifier through the detector were displayed in a real oscilloscope and the developed virtual oscilloscope to test this feature. It was noticed that results from both MCAs and oscilloscopes were highly compatible with each other. It is concluded that the developed virtual MCA supported by the virtual oscilloscope could be used like a real one.

Multichannel vibration analyzer for dynamic systems

Multichannel vibration analyzer for dynamic systems

A fusion approach for evaluating ground conditions for seismic microzoning at the Egyptian Solar Park in Benban, Aswan

Seismic microzoning is the process of mapping out and comprehending the differences in ground motion due to earthquakes in a certain location. Accurate seismic microzoning is vital for the development and safety of buildings and infrastructure in earthquake-prone locations. In this work, we present the application of microtremors, multichannel analysis of surface and machine learning approaches for seismic microzoning at Benban Solar Park in Aswan, Egypt. The findings of the investigation indicated that the ground at Benban Solar Park was generally stiff, with certain regions having stronger stiffness and damping qualities than others. The data also indicated variances in the ground conditions at various sites inside the solar park, with certain regions having a greater risk of ground motion due to earthquakes. Overall, the combination of microtremors, multichannel analysis, and machine learning has shown to be an excellent strategy for correctly and effectively mapping out the ground conditions at Benban Solar Park and assuring the safety and structural integrity of the solar power plants at the park. Moreover, the results of the research could be used to guide the design and construction of the future solar power plants at the park and to examine the safety and structural integrity of the solar park. Furthermore, the application of these techniques not only ensures the safety and structural integrity of the solar power plants at Benban Solar Park, but also promotes sustainable development by providing valuable information for the design and construction of future solar power plants at the park, in line with the principles of environmentally-conscious and responsible development.

Characterization of diamond radiation detector with B-doped/undoped stacked structure

In this study, a radiation detector made of polycrystalline diamond was characterized by neutron and alpha particle. The detector consisted of a boron (B)-doped/undoped stacked structure, where the alpha particles were irradiated from the B-doped layer side. Radiation signals obtained by the multichannel analyzer were compared, and bias dependence was investigated. Results indicate that the formation of the B-doped layer modifies band structure at B-doped/undoped interface, which improving signal hole collection.

Improved multivariate multiscale sample entropy and its application in multi-channel data.

Entropy, as a nonlinear feature in information science, has drawn much attention for time series analysis. Entropy features have been used to measure the complexity behavior of time series. However, traditional entropy methods mainly focus on one-dimensional time series originating from single-channel transducers and are incapable of handling the multidimensional time series from multi-channel transducers. Previously, the multivariate multiscale sample entropy (MMSE) algorithm was introduced for multi-channel data analysis. Although MMSE generalizes multiscale sample entropy and provides a new method for multidimensional data analysis, it lacks necessary theoretical support and has shortcomings, such as missing cross-channel correlation information and having biased estimation results. This paper proposes an improved multivariate multiscale sample entropy (IMMSE) algorithm to overcome these shortcomings. This paper highlights the existing shortcomings in MMSE under the generalized algorithm. The rationality of IMMSE is theoretically proven using probability theory. Simulations and real-world data analysis have shown that IMMSE is capable of effectively extracting cross-channel correlation information and demonstrating robustness in practical applications. Moreover, it provides theoretical support for generalizing single-channel entropy methods to multi-channel situations.

IMPACT OF EXTRACELLULAR WATER ON BLOOD PRESSURE DEPENDING ON AGE AND GENDER IN THE CROSS SECTION STUDY KARDIOVIZE 2030

Objective: A random sample of 2146 volunteers from the Brno population aged 25-64 (1173 women and 973 men) was selected as part of the Kardiovision 2030 cross-section study. Study participants were approached based on the databases of health insurance companies and examined using the Czech Post-MONICA Study methodology. Design and method: Data from the Kardiovize 2030 study were used for the purposes of the work. Basic anthropometric data, blood pressure values, history of hypertension and measurements by direct segmental multifrequency bioelectrical impedance method were obtained. Study participants were approached based on the databases of health insurance companies. We characterized the majority of hypertensives in our group with simple parameters such as fat tissue and body water in different compartments by multichannel bioimpedance analysis. Results: The chance of hypertension occurs when the extracellular water (ECW) increases by 1 L The Impact of extracellular water demonstrated by spatial thin-plate models increase with age. Conclusions: The impact of extracellular water on the level of pressure is statistically significant against the normotonic population. Extracellular pressure has a major influence on systolic pressure and its influence increases with age. The impact of ECW is greater in women.

An Antijamming Method Based on Multichannel Singular Spectrum Analysis and Affinity Propagation for UWB Ranging Sensors

Ultra-wideband impulse radio system has received extensive attention due to their high resolution and poor interception possibility. But the specific electromagnetic threat posed by its complex work environment cannot be ignored. In all kinds of active jamming signals, smart noise jamming plays an important role in modern radar electronic warfare, and most traditional anti-jamming methods have less suppression effect. In this paper, the mechanism of smart noise jamming on the UWB ranging sensor is discussed first. On this basis, an anti-smart noise jamming method based on multichannel singular spectrum analysis and kurtosis characteristic is proposed. Experiments show that smart noise jamming is more threatening to the UWB system than other noise modulation jamming. And the improved algorithm proposed in this paper can suppress the jamming better. After the anti-jamming processing, the average detection probability can reach more than 95%. Meanwhile, the method is improved by adding the affinity propagation (AP) clustering algorithm to solve the underdetermined signal separation problem in the case of compound jamming. The advantage is that it does not have to estimate the number of signals first. Even if the SJR is -10 dB, the waveform similarity between the separation signal and the source signal can reach 0.7 or more.

Determination of Elastic Properties of Soils around a Typical Erosion-Prone Area in Benin City, South-South Nigeria

Soil properties play a crucial role in understanding the mechanisms of erosion and consequently developing appropriate mitigation strategies. The aim of this study is to determine the elastic parameters of soil in an erosion-prone area using the Multichannel Analysis of Surface Wave (MASW) method of geophysical exploration. The active method MASW was adopted for this study. Data were acquired using a 24-channel ABEM Terralock MATK-6 seismograph with geophones of frequency 14Hz. An 8 Kg hammer was used as a source to generate seismic energy. Data acquired were processed with SeisImager2D refraction software developed by Geometric Earth Science Ltd and 2-D shear wave (Vs) and P-wave (Vp) velocities were generated alongside 2-D profiles of Shear Modulus, Young’s Modulus, Bulk Modulus, and Poison’s Ratio. The result of this study reveals soft to medium-stiff saturated clay/dry sand/wet sand and medium-stiff to stiff saturated clays/dry sand/wet sand with shear wave velocity values ranging from 84 m/s to 504 m/s. The bulk modulus, shear modulus, poison’s ratio, and Young’s modulus range from 3.4 GPa to 5.9 GPa, 20 kPa to 440 kPa, 0.448 to 0.498, and 50 kPa to 1.05 GPa respectively.

Short-Term Traffic Speed Prediction for Multiple Road Segments

Short-term traffic prediction has been an essential part of real-time applications in modern transportation systems for the last few decades. Despite the recent progress in the voluminous models and data sources, many existing studies have focused on prediction for either a single or a few locations. In addition, the spatiotemporal dependency in the traffic data was narrowly accounted for. Therefore, this paper finds a new short-term traffic speed prediction algorithm that can efficiently cope with the complexity and immensity of the prediction process derived from the network size and amount of data in order to provide accurate predictions in real time. This algorithm consists of two modules: (a) principal component analysis (PCA) for data dimensionality reduction and feature selection, and (b) multichannel singular spectral analysis (MSSA) for multivariate time-series data prediction. A large amount of traffic data is efficiently compressed by PCA with high accuracy, then used as an input in the multivariate time-series analysis. The algorithm was compared with a vector autoregressive (VAR) model to predict traffic speeds five minutes ahead for a 21.3-mile-long highway segment, using the traffic detector data, and for 451-mile-long segment, using probe-based speed data in Tennessee. The tested algorithm is found to provide accurate predictions with a computation time of less than one second without training. Furthermore, the algorithm shows a better prediction performance under congested flow conditions, compared to VAR. This indicates that the tested algorithm is suitable for real-time prediction and scalable for a large network analysis.

Geological-geotechnical investigations of the historical Diriyah urban zone in Riyadh, Saudi Arabia: an integrated approach

One hundred seventy geotechnical boreholes, two geo-seismic profiles of multichannel analyses of surface waves (MASW), and two geoelectrical cross-sections of electrical resistivity tomography (ERT) were carried out in the historical Diriyah urban zone. The borehole samples were analyzed for the geotechnical parameters of the standard penetration test (SPT N-value), the rock quality designation (RQD), and compressive strength (CS). Moreover, P- and S-wave velocities have been calculated. The measured SPT N-value has been corrected to amend the N60 parameter. According to the corrected N60, type, lithological, and soil profiles were divided into five distinct subsurface layers. It is indicated, for all recorded depths, these sediments become denser with depth where the values of N60 increase from 5 to 88 downward. According to grain size distribution, the major part of soil sites is composed of sand and varies from low to medium compressibility. The estimated RQD values range from 5 to 100 indicating rocks with significant variations in their geotechnical and physio-chemical characteristics. Furthermore, the compressive strength varies widely between 152.3 and 1,104.2 kg/cm2, which represents diverse geodynamic behavior under civil engineering constructions. Besides, the range of soil stiffness is indicated by the Shear-wave velocity (Vs) for soil layers, which varies from 171.3 to 456.2 m/s. According to the findings of the MASW profiles, the shear wave velocity is shown to be decreasing in MASW profile 1 between depths of 8 and 14 m, where the values range from 1,000 to 1,500 m/s, indicating a weak zone filled with secondary materials. But line 2 shows how the shear wave velocity decreased from depths of 5 m–11 m, where values ranged from 1,000 to 1,500 m/s, thus indicating a weak zone. The low resistivity zones in ERT cross-sections, which are found at the same depths in MASW profiles, are well associated with these findings. It can be concluded that there are a number of weak zones with varying depths, shapes, and dimensions found in the historical Diriyah urban zone’s near-surface deposits that civil engineers, urban planners, and urban developers should consider before undertaking any construction or developmental work involving civil engineering.

Active and passive seismic methods for site characterization in Nuweiba, Gulf of Aqaba, Egypt

Nuweiba is located on the western coast of the Gulf of Aqaba (GoA), which represents the southern part of the Gulf of Aqaba - Dead Sea transform fault (GoA-DST). The GoA is characterized by high seismic activity and is the source of the November 22, 1995, Nuweiba earthquake, with a moment magnitude of Mw 7.3. This seismic unrest caused extensive damage in the city of Nuweiba due to the strong shaking caused by the earthquake. In addition, soil amplification triggered by the thick soft-sediments of the Wadi Watir delta beneath the city amplified the destructive power of the event. Therefore, an assessment of the effect of the Wadi Watir sediments on the ground motion at Nuweiba is very important for future construction, seismic hazard assessment, and seismic risk mitigation. Accordingly, the goal of the current study is to define the amplification characteristics of the Wadi Watir deposits using microtremor and surface wave data sets. The horizontal-to-vertical spectral ratio (HVSR) technique is applied to the microtremor data and Multichannel Analysis of Surface Waves (MASW) is applied to the surface wave data. The data are processed to obtain the distribution of the fundamental resonance frequency (F0), the depth of the geophysical bedrock using joint inversion of the Rayleigh wave dispersion curve and ellipticity peak, the shear wave velocity structure, the time-averaged shear-wave velocity in the topmost 30 m (Vs30), and the shear wave transfer function. The results of the HVSR show that F0 in the northern part of the city is 4.2–5.2 Hz and 0.5–0.8 Hz in the middle of the city. Bedrock depth is found to be in the range of 27 and 199 m. The one-dimensional velocity structure obtained from the MASW measurements has resolved two sedimentary layers within the upper 15 m. The Vs30 ranges between 207 and 556 m/s, according to the Vs30 the soil in the study area is categorized into soil classes B and C according to Eurocode 8. The obtained shear wave transfer functions show that the highest amplification factors are observed in the middle part of the study area.

If unpartnered at the birth of a child, how would you fare? A life-course perspective on contemporary single motherhood

ABSTRACT In this article, we use population-based administrative data and multichannel sequence analysis to investigate the trajectories of single mothers in Norway who had a child while unpartnered in 1993, 2001 and 2008. Our observation period is from 1994 to 2015. This period covers several structural transformations in Norwegian society and changes in family policies and welfare policies concerning single mothers. Furthermore, the period saw the growth of alternatives to the nuclear family as the prevailing normative ideal. Our findings demonstrate both complexity and heterogeneity among single mothers and their trajectories. Even so, the population of this group of single mothers is both younger and have lower education than the comparable population of non-single mothers. Nearly half of the single mothers followed trajectories characterized by strong labour market integration and family re-establishment. The other half followed more precarious trajectories characterized by unemployment and health related benefits. Importantly, age and life stage have strong implications for the labour market and family trajectories. Thus, early parenthood combined with leaving school early increases the probability of following precarious trajectories. The results further suggest that both economic cycles and changing welfare state framework is of great importance for single mother trajectories.

A Comparative Analysis for Defining the Sliding Surface and Internal Structure in an Active Landslide Using the HVSR Passive Geophysical Technique in Pujilí (Cotopaxi), Ecuador

Geophysical techniques were employed to analyze one of the landslides that affected the main access road to Pujilí (Ecuador). A passive seismic technique was utilized to test a total of 70 horizontal to vertical spectral ratio (HVSR) points, complemented by an active seismic-refraction profile and a multichannel analysis of surface waves (MASW) survey. The results from the active geophysical surveys facilitated the determination of the shear-wave-velocity value for the surface materials that were in motion. However, the HVSR provided the fundamental frequency fo and amplification Ao values of the ground. The Nakamura (1989) relationship was applied to obtain the thickness of the sediments over a compact material from the fundamental frequency of the terrain in a two-layer model. Additionally, constrained models of the shear-wave velocity (Vs) distribution in the landslide area, obtained from the active seismic surveys, were used to invert the ellipticity curves. The results from this inversion were compared with those obtained by applying the Nakamura equation. The landslide-rupture surface was delineated for each type of analysis, which verified the correlation and minimal differences between the results of the three proposed studies, thus validating the procedure. The directivity of the microtremor HVSR signals was also analyzed, demonstrating a relationship with the internal structure of the sliding material. Furthermore, the ability to slide concerning the Kg parameter (vulnerability index, Nakamura, 1989) was studied. The usefulness of the directivity analysis in defining the internal structures in landslide materials and in determining the areas with the most significant instability was demonstrated. Overall, the HVSR is considered valuable when conducting early landslide studies and is helpful in determining the rupture plane while remaining a simple, fast, and economical technique.

Long-term ambient seismic interferometry for constraining seasonal subsurface velocity variations in urban settings: a distributed acoustic sensing (DAS) case study

SUMMARY Ambient seismic interferometry of distributed acoustic sensing (DAS) data acquired on optical fibre arrays is an increasingly common approach for subsurface investigation. The fixed infrastructure and low maintenance costs of commodity telecommunications fibre also supports cost-effective DAS-based seismic monitoring solutions over extended periods of time—especially when using repurposed telecommunication fibre infrastructure in urban settings. To investigate whether ambient waveform data acquired on such an urban DAS array are sensitive to seasonal subsurface variations, we present a case study using ‘semi-continuous’ DAS time-series data with hourly 150 s sampling windows that were acquired over a 10-month interval in the central business district of Perth, Australia. We apply a cross-coherence analysis to transform pre-processed ambient waveform data into sliding-window weekly interferometric virtual shot gathers (VSGs). We then use these data volumes to compute time-lapse velocity–dispersion panels, which we input to a multichannel analysis of surface waves (MASWs) to generate depth-averaged S-wave velocity estimates of the top 30 m ($V_{S_{30}}$ ). Our time-lapse analyses show that weekly stacked interferometric VSGs exhibit up to 5.8 per cent variations in observed surface wave traveltimes whereas the MASW inversion results capture up to 9.4 per cent variations in $V_{S_{30}}$ estimates between the winter and spring months. We note that these observations are inversely correlated with time-averaged rainfall patterns in the Perth Metro region and are likely attributable to the associated seasonal variations in near-surface groundwater content. Overall, our analysis suggests that semi-continuous ambient seismic monitoring on urban DAS fibre arrays is a computational tractable acquisition strategy that records data volumes useful for monitoring the seasonal variability of groundwater resources beneath urban centres as well as potentially other time-lapse subsurface behaviour occurring over calendar time.

Three dimensional seismic data reconstruction based on truncated nuclear norm

The rank reduction method is widely used to reconstruct three dimensional (3D) seismic data. The traditional multichannel singular spectrum analysis (MSSA) utilizes truncated singular value decomposition (TSVD) to approximately solve the rank function of the block Hankel structure matrix constructed by frequency slices of seismic data. However, the TSVD algorithm discards all nonzero singular values except a few largest singular values and ignores the useful seismic information in small nonzero singular values. To further utilize the seismic data information contained in these small singular values, this paper proposes a method to recover 3D seismic data with truncated nuclear norm (TNN). The proposed method imposes different constraints on large singular values and small singular values. Essentially, the TNN is closer to the rank function than the TSVD. Finally, the proposed model is addressed by the alternating direction method of multipliers, and closed-form solutions are used to update the optimization variables. The experimental results demonstrate that the proposed method achieves superior reconstruction results than the traditional MSSA method.

The effect of saturation and salts on the rigidity of fine-grained material

Repeated multi-channel analysis of surface waves (MASW) and horizontal to vertical spectral ratio (HVSR) experiments were conducted on a hummock within a large landslide in east-central Utah adjacent to a small wetland. Stakes were placed into the ground to ensure identical array geometries and geophone locations. The landslide is an admixture of fine-grained material (clay, quartz and Na-plagioclase) and intermediate-composition volcanic clasts. A prominent crust of Na-salts covered the hummock surface, produced by evapotranspiration of shallow groundwater associated with the adjacent fen.The experiments produced three primary observations. First, on any given day, the Rayleigh wave frequency spectra were highly reproducible between individual experiments. Second, from May to October the spectra exhibited high variability between experiments conducted weeks apart, especially at frequencies <20 Hz. Third, a persistent subsurface boundary exists across which Vs increases from ~175 to ~300 m/s. However, that boundary migrated over time from a depth of ~5 to ~4 m.The low velocity of the upper ~5 m subsurface layer represents poorly-compacted landslide material, perhaps weakened from high Na+ concentrations. However, the variability in frequency spectra and upward migration of the boundary must have arisen from changing moisture and salt content over time. The fen was instrumented with a piezometer that showed an overall ~1 m decline in water levels from May to October with small, superimposed recharge events resulting from summer monsoon rains.This study leads to two important conclusions. Specific to this site and perhaps others, variable moisture content can affect capillary forces and the proportion of evaporite cements in the shallow subsurface that are manifested in strikingly different frequency spectra and migrating stiffness (Vs) boundaries. More generally, moisture and salt content can affect estimates of subsurface stiffness, including the position of apparent boundaries within unconsolidated materials.