What Do P-Wave Velocities Tell Us About the Critical Zone?

Fractures in Earth's critical zone influence groundwater flow and storage and promote chemical weathering. Fractured materials are difficult to characterize on large spatial scales because they contain fractures that span a range of sizes, have complex spatial distributions, and are often inaccessible. Therefore, geophysical characterizations of the critical zone depend on the scale of measurements and on the response of the medium to impulses at that scale. Using P-wave velocities collected at two scales, we show that seismic velocities in the fractured bedrock layer of the critical zone are scale-dependent. The smaller-scale velocities, derived from sonic logs with a dominant wavelength of ~0.3 m, show substantial vertical and lateral heterogeneity in the fractured rock, with sonic velocities varying by 2,000 m/s over short lateral distances (~20 m), indicating strong spatial variations in fracture density. In contrast, the larger-scale velocities, derived from seismic refraction surveys with a dominant wavelength of ~50 m, are notably slower than the sonic velocities (a difference of ~3,000 m/s) and lack lateral heterogeneity. We show that this discrepancy is a consequence of contrasting measurement scales between the two methods; in other words, the contrast is not an artifact but rather information—the signature of a fractured medium (weathered/fractured bedrock) when probed at vastly different scales. We explore the sample volumes of each measurement and show that surface refraction velocities provide reliable estimates of critical zone thickness but are relatively insensitive to lateral changes in fracture density at scales of a few tens of meters. At depth, converging refraction and sonic velocities likely indicate the top of unweathered bedrock, indicative of material with similar fracture density across scales.

Nanoscale Elastoplastic Wrinkling of Ultrathin Molecular Films

Ultrathin molecular films deposited on a substrate are ubiquitously used in electronics, photonics, and additive manufacturing methods. The nanoscale surface instability of these systems under uniaxial compression is investigated here by molecular dynamics simulations. We focus on deviations from the homogeneous macroscopic behavior due to the discrete, disordered nature of the deformed system, which might have critical importance for applications. The instability, which develops in the elastoplastic regime above a finite critical strain, leads to the growth of unidimensional wrinkling up to strains as large as 0.5. We highlight both the dominant wavelength and the amplitude of the wavy structure. The wavelength is found to scale geometrically with the film length, λ∝L, up to a compressive strain of ε≃0.4 at least, depending on the film length. The onset and growth of the wrinkling under small compression are quite well described by an extended version of the familiar square-root law in the strain ε observed in macroscopic systems. Under large compression (ε≳0.25), we find that the wrinkling amplitude increases while leaving the cross section nearly constant, offering a novel interpretation of the instability with a large amplitude. The contour length of the film topography is not constant under compression, which is in disagreement with the simple accordion model. These findings might be highly relevant for the design of novel and effective wrinkling and buckling patterns and architectures in flexible platforms for electronics and photonics.

The controls on earthquake ground motion in foreland-basin settings: The effects of basin and source geometry

Summary Rapid urban growth has led to large population densities in foreland basin regions, and therefore a rapid increase in the number of people exposed to hazard from earthquakes in the adjacent mountain ranges. It is well known that earthquake-induced ground shaking is amplified in sedimentary basins. However, questions remain regarding the main controls on this effect. It is, therefore, crucial to identify the main controls on earthquake shaking in foreland basins as a step towards mitigating the earthquake risk posed to these regions. We model seismic-wave propagation from range-front thrust-faulting earthquakes in a foreland-basin setting. The basin geometry (depth and width) and source characteristics (fault dip and source-to-basin distance) were varied, and the resultant ground motion was calculated. We find that the source depth determines the amount of near-source ground shaking and the basin structure controls the propagation of this energy into the foreland basin. Of particular importance is the relative length scales of the basin depth and dominant seismic wavelength (controlled by the source characteristics), as this controls the amount of dispersion of surface-wave energy, and so the amplitude and duration of ground motion. The maximum ground motions occur when the basin depth matches the dominant wavelength set by the source. Basins that are shallow compared with the dominant wavelength result in low-amplitude and long-duration dispersed waveforms. However, the basin structure has a smaller effect on the ground shaking than the source depth and geometry, highlighting the need for understanding the depth distribution and dip angles of earthquakes when assessing earthquake hazard in foreland-basin settings.

Detection of Karst Cavity Beneath Cast-in-place Pile Using Instantaneous Phase Difference of Two Receiver Recordings

Karst cavities beneath bored cast in situ piles are hazardous to the stability of infrastructure projects. Therefore, it is important to detect karst cavities during the construction of piles. Downward looking sonar deployed at the bottom of a pile hole can be used to detect cavities, however, interference of multiple reflected surface waves from the walls of the pile hole masks the weak cavity reflections. We introduce a sonar method that exploits the instantaneous phase difference between signals recorded at two receivers to detect karst cavities beneath piles. The receiver separation is set to half the dominant wavelength of surface waves propagating along the pile hole. We define Instantaneous Phase Difference Intensity (IPDI) as an index that measures the similarity of instantaneous phase between the signals at the two receivers. Higher IPDI signifies that the two signals have similar instantaneous phase at that time, which implies the arrival of a reflection from a cavity. Reflected surface wave arrivals exhibit low IPDI by design of the receiver geometry. Thus, the first break of reflected P-waves from the roof and floor of a cavity can be identified. We evaluate the effectiveness of the IPDI based analysis method using numerical tests simulating varying depth, azimuth and size of karst cavities. A prototype using the IPDI analysis demonstrates the application of the new pile hole sonar method at two field investigations. Advance drilling, borehole optical image logs and cross-hole tomography verify the IPDI detection results. We conclude that the two-receiver sonar instrumentation along with the IPDI analysis are effective for detecting cavities beneath piles.

A Study on the Effect of Light Sources on the Colour of Objects

Lighting is one of the basic aspects that eases our lives and increases its quality. We use lighting tools in many places such as homes, streets, work places, hospitals, factories, etc. In this study, the effects of the light source and the surface of the object on features like colour temperature, glare, colour (perceived) and dominant wavelength is analysed. Four light sources such as a warm white halogen lamp, warm white LED source and two cool white LED sources were used. In the light measurements, 10 paper surfaces and 8 cloth surfaces were selected as the surface type. Colours of the surfaces were selected among the main colours on the colour locus. Light, reflected from surface was recorded with Konica Minolta CS-200 model. All results were indicated and compared with each other.

Spectral measure of color variation of black - orange - black (BOB) pattern in small parasitic wasps (Hymenoptera: Scelionidae), a statistical approach

A group of eight scelionid genera were studied by means of microspectrophotometric measurements for the first time. The orange and black colors were analyzed quantitatively, which in combination with Functional Data Analysis and statistical analysis of Euclidean distances for color components, describe and test the color differences between genera. The data analyzed by means of Functional Data Analysis proved to be a better method to treat the reflectance data because it gave a better representation of the physical information. When comparing the differences between curves of the same color but different genera, maximum differences were present in different ranges of the spectra, depending on the genus. Reflectance spectra were separated into their spectral color components contributions (red, blue and green). Each component had its own dominant wavelength at the maximum of the spectrum. We found differences in the dominant wavelength for specimens of the same genus, which are equivalent to differences in the hue. A correlation between the mean values of characteristics of the color components was used in an attempt to group the genera that show similar values. The spectral blue components of the orange and black areas were almost identical, suggesting that there is a common compound for the pigments. The results also suggest that cuticle from different genera, but with the same color (black vs black, orange vs orange) might have a similar chemical composition.

Application of data mining techniques for the investigation of track geometry and stiffness variation

Railway tracks are one of the most important national assets of many countries. The major part of the annual budget of railway companies concerns repairing, improving, and maintaining railway tracks, which is a challenge for railway managers. The logical method of repair and maintenance should take into account all the economic and technical aspects of the problem and proper management of track maintenance—without knowing the factors and parameters responsible for the track failure—quality control methods, and finally, the choice of the appropriate repair methods. Railway track geometry is the main factor that identifies the track behavior and condition. It is based on measuring the geometric parameters of the track determined by the track quality indices. The existing track quality indices mostly represent the geometrical condition of the railway track superstructure. In the past years, the effects of track bed stiffness on the track condition have been investigated. This paper investigates the railway track condition based on the railway track geometry parameters as well as the vertical track stiffness. A method for continuous measurement of track stiffness along a railway line is described and demonstrated. By measuring the track geometry parameters and stiffness, the superstructure and the substructure condition of the railway track are assessed. In addition, the relation between these data is investigated by using data mining techniques such as classification, decision tree, clustering, and dominant wavelength filtering. It is shown that filtering the data based on the dominant wavelength provides the best correlation between the track geometry in the vertical direction and stiffness.