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Friction velocity (u*) is an important velocity scale used in the study of engineering and geophysical flows. The widespread use of 2D sonic anemometers in modern meteorological stations makes the estimation of u* from just the horizontal components of the velocity a very attractive possibility. The presence of different wind regimes (such as sea breezes in or near coastal zones) causes the turbulent parameters to be dependent on the wind direction. Additionally, u* depends on atmospheric stability, whch makes the estimation of u* from 2D measurements very difficult. A simple expression is proposed, and then tested with data from six independent experiments located in coastal zones. The results show that it is possible to estimate friction velocity from 2D measurements using the turbulence intensity as a proxy for u*, reducing substantially the sensitivity to the wind direction or atmospheric stability, with small root mean squared errors (0.06 < RMSE < 0.097) and high correlation coefficients (0.77 < r2 < 0.95).

In this study, the crustal shear velocity structure beneath the Indo-Burma Ranges (IBR) is estimated using inversion modeling of the receiver functions computed at seismic stations operated during 2011–2018. The inversion results describe significant variations in the shear-wave velocity (Vs), velocity ratio (Vp/Vs) and crustal thickness in and around the IBR. The Moho deepens from 41 km in the west to 70 km in the east of the IBR. It is also observed that most of the earthquakes are confined to the crust in the west of the Indo-Burma arc, whilst the east of the IBR is associated with sub-crustal earthquakes, supporting the fact that the Indian plate is dipping beneath the Burma Plate. The dip angle of the Moho in the north of the IBR is smaller (7.8o) than that in its south (9.5o). We found that an average crustal Vs of 3.5 km/s for the highest value of the Vp/Vs ratio (> 1.8) was prevalent at all the stations in the IBR, associated with mafic prehnite-pumpellyite facies basalt and hydroxyl zeolite facies basalt, which suggests that the subducting Indian slab beneath the Myanmar microplate in and around the IBR is under a state of dehydration, where intra-slab earthquakes at varying depths (> 50 km) occur. This observation is highly consistent with the earlier 3-D tomographic results obtained independently.

Normal stress changes occur commonly during fault and rock joint rupture, and play a key role in determining frictional behavior and shear stability of these discontinuities. Previous experimental studies of the direct shear test under cyclic normal loads confirm that there exists a phase shift between peak normal stress and peak shear stress, as well as between peak friction coefficient and peak shear stress with shear stress and friction coefficient lagging. However, the underlying physics of this finding is poorly understood. Here, we present a numerical study to investigate the effect of cyclic normal loads on the friction of smooth joints. Our simulations show reasonable agreements with experimental observations, verifying the capability of the proposed model based on the discrete element method. We also investigate the effect of normal loading rate, dynamic amplitude, static normal stress level, shear velocity, and joint stiffness on the frictional behavior of the joint. From a microscopic point of view, we focus on the underlying processes of the phase shift between the peak shear stress (friction coefficient) and peak normal loads. We find that phase shift is related to the changes of the population of slipping and frozen contacts, and also the evolutions of shear force, shear velocity, and shear displacement of individual contacts, in which the macroscopic shear velocity plays a significant role. Inhomogeneous stress distributions near the joint indicate that damage or failure should occur in some contact-scale regions, although which is not directly verified due to the limitations of the presented model. Our work improves the understanding of the physics on how normal load perturbations affect the shear behavior of smooth rock joints.

Comprehensive preview of flow characteristics and bedforms in rivers is one of the imperative purposes of river restoration projects. This study aimed to assess the application of double averaged technique for estimating the flow velocity and shear velocity in gravel bedforms by field research throughout the Babolroud River in north of Iran. Also, quadrant analysis carried out to investigate the turbulence structure over a pool-riffle bedforms. Based on data collected in a 95 m reach with variable width and using Acoustic Doppler Velocimeter (ADV), a double averaged velocity profile was obtained. This method validation was conducted by logarithmic law and also boundary layer characteristics method for shear velocity estimation within the bedform. The results demonstrate that the double averaged velocity profile was fitted on the logarithmic law in the inner layer and deviated from it in the outer layer, as was expected. On the other hand, the calculated shear velocity by two methods of logarithmic law and boundary layer characteristics was consistent and had small discrepancies, which indicates the double averaged method validity. The results of quadrant analysis illustrated the ejections and sweeps, as a dominant bursting event near the bed and water surface in the pool center, respectively.

SUMMARY Measurements of various physical properties of oceanic sediment and crustal structures provide insight into a number of geological and geophysical processes. In particular, knowledge of the shear wave velocity (VS) structure of marine sediments and oceanic crust has wide ranging implications from geotechnical engineering projects to seismic mantle tomography studies. In this study, we propose a novel approach to nonlinearly invert compliance signals recorded by colocated ocean-bottom seismometers and high-sample-rate pressure gauges for shallow oceanic shear wave velocity structure. The inversion method is based on a type of machine learning neural network known as a mixture density neural network (MDN). We demonstrate the effectiveness of the MDN method on synthetic models with a fixed deployment depth of 2015 m and show that among 30 000 test models, the inverted shear wave velocity profiles achieve an average error of 0.025 km s−1. We then apply the method to observed data recorded by a broad-band ocean-bottom station in the Lau basin, for which a VS profile was estimated using Monte Carlo sampling methods. Using the mixture density network approach, we validate the method by showing that our VS profile is in excellent agreement with the previous result. Finally, we argue that the mixture density network approach to compliance inversion is advantageous over other compliance inversion methods because it is faster and allows for standardized measurements.

We analyze data from passive and active seismic experiments conducted in the Adventdalen valley of Svalbard in the Norwegian Arctic. Our objective is to characterize the ambient wavefield of the region and to investigate permafrost dynamics through estimates of seismic velocity variations. We are motivated by a need for early geophysical detection of potentially hazardous changes to permafrost stability. We draw upon several data sources to constrain various aspects of seismic wave propagation in Adventdalen. We use f-k analysis of five years of continuous data from the Spitsbergen seismic array (SPITS) to demonstrate that ambient seismic noise on Svalbard consists of continuously present body waves and intermittent surface waves appearing at regular intervals. A change in wavefield direction accompanies the sudden onset of surface waves when the average temperature rises above the freezing point, suggesting a cryogenic origin. This hypothesis is supported further by our analysis of records from a temporary broadband network, which indicates that the background wavefield is dominated by icequakes. Synthetic Green’s functions calculated from a 3D velocity model match well with empirical Green’s functions constructed from the recorded ambient seismic noise. We use a shallow shear-wave velocity model, obtained from active seismic measurements, to estimate the maximum depth of Rayleigh wave sensitivity to changes in shear velocity to be in the 50–100 m range. We extract seasonal variations in seismic velocities from ambient noise cross-correlation functions computed over three years of SPITS data. We attribute relative velocity variations to changes in the ice content of the shallow (2–4 m depth) permafrost, which is sensitive to seasonal temperature changes. A linear decreasing trend in seismic velocity is observed over the years, most likely due to permafrost warming.

Non-erodible elements such as stones and vegetation are key to controlling wind erosion and dust emission in drylands. Stony deserts are widely distributed in the Gobi Desert, but the effect of stones on wind erosion and dust emission have not been well studied, except under artificial conditions. In this study, we evaluated the effect of stones on wind erosion and dust emission by measuring the sand saltation threshold in a stony desert in Tsogt-Ovoo in the Gobi Desert, Mongolia, under natural surface conditions during sand and dust storms. We quantified the amount of stones by measuring the roughness density, and determined the threshold friction velocity for sand saltation by measuring wind speed and sand saltation count. Our results showed that the threshold friction velocity increased with the roughness density of stones. In the northern part of the study area, where neither a surface crust nor vegetation was observed, the roughness density of stones was 0.000 in a topographic depression (TD), 0.050 on a northern slope (N.SL), and 0.160 on the northern mountain (N.MT). The mean threshold friction velocity values were 0.23, 0.41, and 0.57 m/s at the TD, N.SL, and N.MT sites, respectively. In the southern part of the study area, the roughness density values of stones were 0.000 and 0.070–0.320 at the TD and southern slope sites, respectively, and the mean threshold friction velocities were 0.23 and 0.45–0.71 m/s, respectively. We further compared the observed threshold friction velocities with simulated threshold friction velocities using Raupach’s theoretical roughness correction and the measured roughness density values, and found that Raupach’s roughness correction worked very well in the simulation of threshold friction velocity in the stony desert. This means that the results of our stone measurement can be applied to a numerical dust model.

SUMMARY Seismic observations indicate that the lowermost mantle above the core–mantle boundary (CMB) is strongly heterogeneous. Body waves reveal a variety of ultra-low velocity zones (ULVZs), which extend not more than 100 km above the CMB and have shear velocity reductions of up to 30 per cent. While the nature and origin of these ULVZs remain uncertain, some have suggested they are evidence of partial melting at the base of mantle plumes. Here we use coupled geodynamic/thermodynamic modelling to explore the hypothesis that present-day deep mantle melting creates ULVZs and introduces compositional heterogeneity in the mantle. Our models explore the generation and migration of melt in a deforming and compacting host rock at the base of a plume in the lowermost mantle. We test whether the balance of gravitational and viscous forces can generate partially molten zones that are consistent with the seismic observations. We find that for a wide range of plausible melt densities, permeabilities and viscosities, lower mantle melt is too dense to be stirred into convective flow and instead sinks down to form a completely molten layer, which is inconsistent with observations of ULVZs. Only if melt is less dense or at most ca. 1 per cent more dense than the solid, or if melt pockets are trapped within the solid, can melt remain suspended in the partial melt zone. In these cases, seismic velocities would be reduced in a cone at the base of the plume. Generally, we find partial melt alone does not explain the observed ULVZ morphologies and solid-state compositional variation is required to explain the anomalies. Our findings provide a framework for testing whether seismically observed ULVZ shapes are consistent with a partial melt origin, which is an important step towards constraining the nature of the heterogeneities in the lowermost mantle and their influence on the thermal, compositional and dynamic evolution of the Earth.

This research proposes a relationship between two methods such as a numerical approach by conducting a microtremor array observation and field survey by using the seismic cone penetration test unit (SCPTu). A database of shear-wave velocity (Vs) measurements was established using the microtremor array technique and seismic cone penetration test unit (SCPTu) on high-quality samples of rock and soft soil in Padang city, Indonesia. The study also demonstrates that the Vs values obtained from the different methods are consistent with the microtremor array technique. This technique may thus be deemed a valuable tool, as it can be used in engineering practice with confidence. Comparison of the Vs for different soils at the first layer between the microtremor array observation results and the SCPTu results exhibited the microtremor array method is unable to determine the Vs at the layer where its Vs changes dramatically, such as at the same layer as station UNP at 2 to 3.5m deep.

The shipboard measurements of whitecap coverage (W) and the meteorological and oceanographic information from two cruises in the South China Sea and Western Pacific are explored for estimating W. This study aims at evaluating how to improve the parameterizations of W while considering the effects of currents and swells on wave breaking. Currents indeed affect W in a way that winds with following currents can decrease W, whereas winds with opposing currents can increase W. Then, 10-m wind speed over sea surface (U10) is calibrated by subtracting the current velocity from U10 when the propagating directions of winds and currents are aligned. By contrast, when the direction is opposite, U10 is calibrated by adding the parallel velocity component of the opposing current to U10. The power fits of W dependence on the U10-related parameters of U10, friction velocity, wind sea Reynolds number in terms of this calibrated-U10 obtain better results than those directly fitted to U10. Different from the effect of currents on W, wind blowing along the crest line of swells may contribute to the increase in W. The conclusions suggest that U10 should be calibrated first before parameterizing W in areas with a strong current or some swell-dominant areas.

Researching the behavior of the river. Especially at the bend, where the morphology of the river is not always straightforward. Flow velocity high water and grinding at river bends occur at different points. This research was conducted on five adjacent bends on the Sidoan River section. This study examined the condition of riverbed sediment, knowing the stability of riverbed sediment granules based on shearing velocity, and stability of riverbed sediment granules based on shear stress. The method used in this study is geometric measurement. Q50 discharge calculation. produces hydraulic simulation. d50 sediment diameter. HEC-RAS software simulation and Shields graphs analysis. The results of the study on five bends for Q50 discharge are the condition of the riverbed in five bends all moving, the critical shear velocity relationship and flow depth are directly proportional, the highest condition at bend 2, otherwise the lowest condition at bend 3. The relationship between particle dimensions and shear velocity is inversely proportional to the value of sliding velocity. if the particle dimensions are small then the large shear stress occurs at bend 5 and vice versa, the dimensions of large particles then the small shear velocity occurs at bend 4, sliding velocity is directly proportional to the shear stress. The highest critical shear stress at bend 2, while the lowest condition at bend 4, the greater the radius of the bend the scouring was deeper.

Seismic input energy per unit mass ( EI/m) imparted into a structure is a function of earthquake (duration, frequency content, amplitude etc.), soil (shear velocity, dominant period etc.) and the structural (vibrational periods etc.) characteristics. Generally, the damping properties of the structure is assumed negligible for seismic input energy. Most of the existing spectral equations derived for SDOF systems generally use a constant damping ratio of 5%. In this study, the damping effect on EI/m is investigated experimentally and numerically on SDOF systems with distinct damping ratios. Experimental investigation and numerical computations proved that seismic input energy is very sensitive to variation of damping within the vicinity of fundamental frequencies. Specifically, up to 50% increment was observed in the plateau region of the input energy spectrum, where maximum EI/m values occur, by variation of damping from 2% to 10%. Hence, a novel damping modification factor ( DMF), which could be utilized for existing energy spectra, is proposed in this paper. Validation studies of the proposed DMF are achieved through the various energy spectra found in the literature.

Generally, the condition of the rivers in Indonesia are alluvial rivers which had meanders, where the change in the river bed topography often occur. One of the parameters associated with changes in the river bed topography is bed-shear velocity, or Reynolds stress. The bed-shear velocity can be calculated by the Reynolds stress distribution method and the Clauser method which commonly used in straight channels. In fact, on natural channel there is a curve and even a meandering channel. With more complex flow conditions, the use of the Clauser method in curved channels can be questioned, is it still accurate or not. In this paper, both methods will be discussed by comparing the measurement data in the laboratory using 180 curved channel with flat bed. The results of data analysis show that the use of these two methods in curved channels produces an average difference of around 19.81%, where the Clauser method gives greater results and better tendencies. Apart from the differences in the results given, it can be said that the Clauser method as well as the Reynolds stress distribution method can still be used to calculate the bed-shear velocity in the curved channel

Convective rolls are two-dimensional convective quasi-lines that can strongly influence phenomena associated with severe weather. They can also influence the urban micro-climate by increasing the surface wind shear. In this study, we aim to theoretically estimate the influence of the urban heat island and of the urban roughness on the dynamics of the convective rolls. To this purpose, we first derive analytical expressions for the vertical velocity of the rolls in the framework of the Monin–Obukhov similarity theory, which depend on the surface heat flux and of the friction velocity. By using the urban surface roughness, parameterized by its drag coefficient, related directly to the friction velocity, we use the obtained expressions of the vertical velocity of the rolls to visually analyze the contribution of surface heat flux and of the urban surface roughness on the rolls’ velocity. We thus prove that the increased heat fluxes associated with urban surfaces have a strong impact on the convective motion, and that the urban surface roughness can influence the rolls’ dynamics over urban heat islands. Finally, we argue that the studies investigating the urban heat island-induced sub-cloud convective flows would be much improved if, besides the surface temperature distributions and the surface heat fluxes, they would include the urban surface roughness.

Mulching is fastest strategy to control sand dune movement in arid and semiarid areas. In the present study the effect of micro silica- cement mixture was evaluated as mulch. For this purpose, an experiment was carried out as a factorial arrangement and a completely randomized design with 3 replicates. Three studied factors included 6 micro silica rates (0 as control, 0.5, 2.5, 5, 7.5 and 12.5 percent), 2 rates of mulch thickness (one and two mm layers) and 2 time series (7 and 60 days). Prepared mulches based on different mixtures of micro silica + sand (400 g) and cement were sprayed on sand trays. Then 4 parameters including shear strength, penetration resistance, threshold friction velocity and soil losses at a wind speed of 15 ms−1 were measured on the studied treatments. Results obtained from the analysis of variances revealed that the effect of micro silica rates, thickness of mulch and time on the studied properties were significant. Mean comparisons also showed that shear strength, penetration resistance and threshold friction velocity increased and soil losses of treatments significantly decreased when the micro silica rates increased. The addition of micro silica to sand- cement mixture increased shear strength and penetration resistance by 76% and 82.5% respectively and decreased soil losses by 100%. The erodibility and mechanical properties of the treatments improved by increasing the thickness of the mulch. Moreover, in all studied treatments more improvements occurred in the mentioned properties of mulches during time. The application 7.5% of micro silica after 60 days was the optimal mulch to improve the soil erodibility and to increase the mechanical resistance against wind erosion.

The size distribution of airborne dust particles is an important parameter in the measurement of dust emissions due to wind erosion, and a quantitative and accurate description is necessary. Observations regarding the size distribution of airborne dust particles are currently lacking in Tibetan Plateau (TP). This study aims to obtain a dust particle size distribution and compare the difference in spatial distribution at a field site (FS) and two urban observation sites (Minfeng and Hetian), in the north of the TP, under the condition of the dust-days and clear-days. The observation data was collected from 5 July to 4 August, 2019. The mass concentration of dust (PM20) was measured with a 10-stage quartz crystal microbalance cascade impactor. The results suggested that 91.9% of the particles were less than 1.4 µm on clear-days, and particles of d ≥ 1.4 µm increased to 27.2% with the occurrence of the dust events. More than 80% of the airborne dust particles were less than 1.4 µm for each friction velocity. The proportion of d 0.7 μm was the greatest at 0.5 m on clear-days. During urban observation, with the occurrence of dust events, the concentration of a particle size greater than 2.5 µm increased most significantly in Minfeng, while the concentration of a particle size less than 0.7 µm increased most significantly in Hetian. Moreover, the proportion of particles with d 1.4 µm had the most obvious difference among these three sites.

In north-west China, extensive areas of gravel desert exist, whose surface properties have an important effect on the wind-erosion threshold friction velocity $$ u_{*t} $$ . In this study, we use four models and field observations of gravel mass fraction, soil physical crust, and soil clay content to assess the effect of gravel-surface properties on the value of $$ u_{*t} $$ . Results show that gravel coverage in north-west China ranges between 0.07 and 1.00 (with a mean of 0.67), and about 81% of the sites investigated are covered by soil physical crust. Clay content is 2.4% on average in the study region, less than 2% in 52.1% of that region, and between 2 and 4% in the remaining study regions. The four regions where clay content is greater than the mean include the western Alxa Plain, the alluvial fan of the western Alxa Plain, the northern Alxa Plain, and the Hexi Corridor. In the study region, the value of $$ u_{*t} $$ ranges between 0.12 and 0.78 m s−1 (with a mean of 0.45 m s−1). Soil moisture, gravel coverage, and soil physical crust all affect the magnitude of $$ u_{*t} $$ . A principal component analysis indicates that the soil crust contributes of about 62% of the $$ u_{{*{\text{t}}}} $$ variations, soil moisture 25%, and surface roughness 9%. A variance analysis shows clear spatial differences in the magnitude of $$ u_{*t} $$ in north-west China due to the spatial variations in gravel land-surface properties.

The mechanical behavior of the joints inside a loess layer is greatly important in weak intercalation studies owing to its involvement in a wide range of landslides in the loess region in China. The shear behavior of the joints in the loess stratum during direct shear and cyclic loadings was investigated using the PFC2D discrete element software. Loess mudstone and mudstone with weak intercalated layer materials were subjected to direct testing, and cyclic shear tests were conducted with consideration to the influence of normal stress and shear velocity. The macroscopic properties and damage patterns were obtained for six numerical configurations; namely, loess-weathered mudstone with 0°, 10°, and −10° joints and weathered mudstone with 0°, 10°, and −10° weak intercalated layers. The numerical test results revealed that, in the direct shear tests, the shear stress and shear displacement of the samples increased with the normal stress. In the cyclic shear tests with a total cycle number N=20, the shear stress-shear strain curve of the six different configurations exhibited a hysteresis loop. The numerical tests also revealed that, under cyclic shear, the normal stress and shear velocity affected the shear strength. The degree of damage increased as the shear velocity decreased from 0.1 mm/s to 0.005 mm/s for all six numerical configurations. Compared with the damage pattern of the direct shear tests, the damage of the cyclic shear tests mainly comprised shear cracks and fractures, some shaking consolidation settlement and fewer shear strain occurred around the joints. In the direct shear tests, more compression cracks and fractures occurred in the samples. The damage mainly developed along the joints, and shearing-off damage occurred. The results obtained by this study further elucidate the failure mechanism and microscopic damage response of the joints in the loess stratum in Northwest China.

A model for the subsurface flow and associated oxygen transfer induced by surface flow and slip velocity is presented in a gravel bed river. The shear velocity (U *) and hydraulic conductivity (K) ...

During 2014–16, a semi-permanent network of four 3-component broadband seismographs was operational in the Rajasthan craton and Aravalli mobile belt in the NW Indian shield. The reliable and accurate broadband data from 16 selected regional Indian earthquakes of Mw 5.5–7.8 from this seismic network enabled to estimate the group velocity dispersion characteristics and one-dimensional regional shear velocity structure of northern India, covering the region below north India between the entire Himalaya (from the Pakistan Himalaya in west to the Burmese arc in the east) and Rajasthan (including Aravalli mobile belt). First, Rayleigh- (at 7–87s) and Love- (at 7–82s) wave group velocity dispersion curves were measured and then these curves were inverted to estimate the crustal and upper mantle structure below north India. It is observed that group velocities are of variable nature within the region. This could be attributed to the complex crust-mantle structure in the study region resulted from the magmatism episodes associated with the Proterozoic collision, 65 Ma Deccan volcanism and the Himalayan collision. The best model in the study region reveals a two-layered crust, with a 15-km thick upper-crust (UC) of average shear velocity (Vs) of 3.12 km/s and a 25-km thick lower-crust(LC) of average Vs of 3.44 km/sec. The modeling detects a drop in Vs (∼1-2%) at 79–120 km depths, underlying north India, representing the probable seismic lithosphere-asthenosphere boundary (LAB) at 79 km depth. A geothermal gradient extrapolated from the surface heat flow (∼74 mW/m2) shows that such a gradient would intercept CO2-bearing mantle peridotite solidus at 100 km depth, and thus could signal the presence of small amounts of partially melted magma below 100 km depth. Therefore, this 1–2% drop in Vs could be attributed to the presence of carbonatite melts in the upper mantle related to magmatic episode of 65 Ma Deccan plume activity as also suggested by existing geological and seismological evidence.

The entrainment and suspension of sand and gravel are important for the evolution of rivers, deltas, coastal areas, and submarine fans. The prediction of a vertical profile of suspended sediment concentration typically consists of assessing (1) the concentration near the bed using an entrainment relation and (2) the upward vertical distribution of sediment in the water column. Considerable uncertainty exists in regard to both of these steps, especially the near-bed concentration. Most entrainment relations have been tested against limited grain-size-specific data, and no relations have been evaluated for gravel suspension, which can be important in bedrock and mountain rivers. To address these issues, we compiled a database with suspended sediment data from natural rivers and flume experiments, taking advantage of the increasing availability of high-resolution grain size measurements. We evaluated 12 dimensionless parameters that may determine entrainment and suspension relations and applied multivariate regression analysis. A best-fit two-parameter equation (r2=0.79) shows that near-bed entrainment, evaluated at 10 % of the flow depth, decreases with the ratio of settling velocity to skin-friction shear velocity (wsi/u∗skin), as in previous relations, and increases with Froude number (Fr), possibly due to its role in determining bedload-layer concentrations. We used the Rouse equation to predict concentration upward from the reference level and evaluated the coefficient βi, which accounts for differences in the turbulent diffusivity of sediment from the parabolic eddy viscosity model used in the Rouse derivation. The best-fit relation for βi (r2=0.40) indicates greater relative sediment diffusivities for rivers with greater flow resistance, possibly due to bedform-induced turbulence, and larger wsi/u∗skin; the latter dependence is nonlinear and therefore different from standard Rouse theory. In addition, we used empirical relations for gravel saltation to show that our relation for near-bed concentration also provides good predictions for coarse-grained sediment. The new relations extend the calibrated parameter space over a wider range in sediment sizes and flow conditions compared to previous work and result in 95 % of concentration data throughout the water column predicted within a factor of 9.

The characteristics of turbulence over mountainous terrain are investigated with an aim to predict propagation of short-wavelength electromagnetic waves (including optical waves). For this purpose, long-term observations of the day- and night-time stratification of atmospheric turbulence are continued at the Sayany solar observatory. A new mobile AMK-03-4 hard-and-software system is used, which is designed for measuring the characteristics of turbulent meteofields. New experimental data are obtained on the turbulent scales of velocity V* (friction velocity) and temperature T*, which are important characteristics in the Monin–Obukhov similarity theory. A comparison of the experimental results with the data obtained by the authors earlier in different periods of time and in different climatic and geographical regions is performed. An experimental validation of the similarity theory postulates in the atmospheric boundary layer is provided. It is shown that the traditional similarity theory can be extended to an arbitrary (e.g., mountainous) boundary layer. This offers a solution to the problem of predicting the characteristics of turbulence in an anisotropic layer, including that in the mountain regions.

Shear and compressional wave velocities, coupled with other petrophysical data, are vital in determining the dynamic modules magnitude in geomechanical studies and hydrocarbon reservoir characterization. But, due to field practices and high running cost, shear wave velocity may not available in all wells. In this paper, a statistical multivariate regression method is presented to predict the shear wave velocity for Khasib formation - Amara oil fields located in South- East of Iraq using well log compressional wave velocity, neutron porosity and density. The accuracy of the proposed correlation have been compared to other correlations. The results show that, the presented model provides accurate estimates of shear wave velocity with correlation coefficient of about unity than other currently available methods.

An inclusion model, based on the Kuster–Toksoz effective medium theory along with Gassmann theory, is tested to forward model velocities for fluid‐saturated rocks. A simulated annealing algorithm, along with the inclusion model, effectively inverts measured compressional velocity (VP) to achieve an effective pore aspect ratio at each depth in a depth variant manner, continuously along with depth. Early Cretaceous syn‐rift clastic sediments at two different depth intervals from two wells [well A (2160–2274 m) and well B (5222–5303 m)], in the Krishna–Godavari basin, India, are used for this study. Shear velocity (VS) estimated using modelled pore aspect ratio offers a high correlation coefficient (>0.95 for both the wells) with measured data. The modelled pore aspect ratio distribution suggests the decrease in pore aspect ratio for the deeper interval, mainly due to increased effective vertical stress. The pore aspect ratio analysis in relation to total porosity and volume of clay reveals that the clay volume has insignificant influence in shaping the pore geometry in the studied intervals. An approach based on multiple linear regression method effectively predicts velocity as a linear function of total porosity, the volume of clay and the modelled pore‐space aspect ratio of the rock. We achieved a significant match between measured and predicted velocities. The correlation coefficients between measured and modelled velocities are considerably high (approximately 0.85 and 0.8, for VP and VS, respectively). This process indicates the possible influence of pore geometry along with total porosity and volume of clay on velocity.

Scour at river bend is a complex process involving various parameters. Experiments were conducted in two laboratory flumes having 90° and 180° bends to study the influence of different parameters on scour at bends. Uniform non-cohesive sediments having median diameters varying from 0.28 to 1.18 mm were used as bed materials under different flow conditions. Three different cross-sectional shapes of the bed, namely flat, trapezoidal and parabolic, were used to study the effect of shape on scour. From the experiments, it is found that, at 90° bend, maximum scour and deposition occurred on concave and convex bank, respectively, between 50° and 60° azimuthal sections, whereas for 180° bend, the location was between 130° and 140° sections. Magnitude of scour was maximum for parabolic bed on the concave bank under flooded condition and deposition was maximum for flat bed on convex side. The deposition pattern on trapezoidal and parabolic bed was also different than that of flat bed. Again, for the same shear velocity ratio, the bigger size bed sediment produced larger scour depth but, for the same bed particle size, scour was more for greater approach shear velocity ratio. Further, measured three-dimensional time averaged velocity components before and after the scour on the 180° bend having initial parabolic bed shows the dominance of a spiral flow at the first half of the bend, and cross-flow from concave to convex at lower layer of the second half of the bend. The combined effect of vortex, cross-flow and accelerated flow is responsible for the erosion on the concave bank and deposition on the convex bank.

Variations in friction velocity with wind speed and height are studied under moderate (≥9 m s−1)-to-strong onshore wind conditions caused by three landfalling typhoons. Wind data are from a coastal 100-m tower equipped with 20-Hz ultrasonic anemometers at three heights. Results show that wind direction affects variations in friction velocity with wind speed. A leveling off or decrease in friction velocity occurs at a critical wind speed of ~20 m s−1under strong onshore wind conditions. Friction velocity does not always decrease with height in the surface layer under typhoon conditions. Thus, height-based corrections on friction velocities using the model from Anctil and Donelan may not be reliable. Surface-layer heights predicted by the model that are based on Ekman dynamics are verified by comparing with those determined by a proposed method that is based on the idea of mean boundary layer using wind-profile data from one of the landfalling typhoons. Friction velocity at the top of the surface layer is then estimated. Results show that friction velocity decreases by about 20% from its surface value and agrees well with previous results of Tennekes.

The current study modifies the representation of the Shields parameter using turbulent strength, i.e. the root-mean-square (rms) fluid velocity. Experiments were done under a steady, uniform flow using eight sediment sizes with particle Reynolds numbers ( R e p ) ranging between 1.0 (fine sediment) and 183.4 (coarse sediment). Utilising the peak rms horizontal ( u ˆ ) values, the critical Shields parameter, θ c , was calculated and a trend similar to the well-established Shields curve was developed. The analysis was extended to the Shields curve obtained based on the critical shear velocity, Reynolds shear stress, and data extracted from the oscillating grid-turbulence experiments. Results show that turbulent fluctuations are crucial for the incipient sediment motion and are essentially better predictors than the commonly used critical shear velocity. A quadrant analysis to identify the role of turbulent bursting events in incipient sediment motion also was done where sweeps and ejections are dominant for finer and coarser sediment sizes, respectively.

This paper experimentally explores the frictional sliding behavior of two simulated gouges: one, a series of quartz–smectite mixtures, and the other, powdered natural rocks, aiming to evaluate and codify the effect of mineralogy on gouge dilation and frictional strength, stability, and healing. Specifically, velocity-stepping and slide-hold-slide experiments were performed in a double direct shear configuration to analyze frictional constitutive parameters at room temperature, under normal stresses of 10, 20, and 40 ​MPa. Gouge dilation was measured based on the applied step-wise changes in shear velocity. The frictional response of the quartz–smectite mixtures and powdered natural rocks are affected by their phyllosilicate content. Frictional strength and healing rates decrease with increasing phyllosilicate content, and at 20 ​wt.% a transition from velocity-weakening to velocity-strengthening behavior was noted. For both suites of gouges, dilation is positively correlated with frictional strength and healing rates, and negatively correlated with frictional stability. Changes in the permeability of gouge-filled faults were estimated from changes in mean porosity, indexed through measured magnitudes of gouge dilation. This combined analysis implies that the reactivation of caprock faults filled with phyllosilicate-rich gouges may have a strong influence on permeability evolution in caprock faults. Keywords: Fault gouge, Mineralogy, Strength and stability, Frictional healing, Gouge dilation, Permeability

A two-dimensional (2D) computational model for simulation of incipient sediment motion for non-cohesive uniform and non-uniform particles on a horizontal bed was developed using the Discrete Element Method (DEM). The model was calibrated and verified using various experimental data reported in the literature and compared with different theories of incipient particle motion. Sensitivity analysis was done and the effects of relevant parameters were determined. In addition to hydrodynamic forces such as drag, shear lift and Magnus force, the particle-particle interaction effects were included in the model. The asymptotic critical mobility number was evaluated for various critical particle Reynolds numbers ( R ∗ ) in the range of very small and very large R*. The obtained curve is classified into four regions. It was found that in the linear region, the drag force has the principal role on the initiation of motion. Moreover, the critical mobility number is independent of particle diameter. A procedure for estimating the critical shear velocity directly from the information on particle diameter and roughness height was developed. Finally, the mechanism of incipient motion for the different regions was studied and the effect of different forces on the incipient particle motion was obtained. It was found that the maximum effects of lift and Magnus forces were, respectively, less than ten and twenty percent of the total force. The drag force, however, was typically the dominant force accounting for majority of the net hydrodynamic force acting on sediment particles at the onset of incipient motion.

It is important to have a reasonable estimation of sediment transport rate with respect to its significant role in the planning and management of water resources projects. The complicate nature of sediment transport in gravel-bed rivers causes inaccuracies of empirical formulas in the prediction of this phenomenon. Artificial intelligences as alternative approaches can provide solutions to such complex problems. The present study aimed at investigating the capability of kernel-based approaches in predicting total sediment loads and identification of influential parameters of total sediment transport. For this purpose, Gaussian process regression (GPR), Support vector machine (SVM) and kernel extreme learning machine (KELM) are applied to enhance the prediction level of total sediment loads in 19 mountain gravel-bed streams and rivers located in the United States. Several parameters based on two scenarios are investigated and consecutive predicted results are compared with some well-known formulas. Scenario 1 considers only hydraulic characteristics and on the other side, the second scenario was formed using hydraulic and sediment properties. The obtained results reveal that using the parameters of hydraulic conditions as inputs gives a good estimation of total sediment loads. Furthermore, it was revealed that KELM method with input parameters of Froude number (Fr), ratio of average velocity (V) to shear velocity (U*) and shields number (θ) yields a correlation coefficient (R) of 0.951, a Nash-Sutcliffe efficiency (NSE) of 0.903 and root mean squared error (RMSE) of 0.021 and indicates superior results compared with other methods. Performing sensitivity analysis showed that the ratio of average velocity to shear flow velocity and the Froude number are the most effective parameters in predicting total sediment loads of gravel-bed rivers.

Power spectra of shear-waves for eighteen earthquakes from the Anza-Imperial Valley region were inverted for source, mid-path Q, site attenuation and site response. The motivation was whether differences in site attenuation (parameterized ast*, r/cQ,whereris distance along ray path near the site,cis shear velocity andQis the quality factor that parameterizes attenuation) and site response could be correlated with residuals in peak values of velocity or acceleration after removing the affect of distance-dependent attenuation. We decomposed spectra of S-waves from horizontal components of 18 earthquakes from 2010 to 2018 into a common source for each event with ω−2spectral fall-off at high frequencies and then projected the residuals onto path and site terms following the methodology of Boatwright et al. (Bull Seismol Soc Am 81:1754–1782, 1991). The site terms were constrained to have an amplification at a particular frequency governed by VS30at two of the sites which had downhole shear-wave logs. The 18 events, 3 20and 1022 dyne-cm, and stress drops between 1 and 100 bars. Average mid-crust attenuation had a Q of 844 reflecting the average path through the crystalline rock of the San Jacinto Mountains.t*for each station corresponded to the geologic environment such that stations on hard rock had lowt*(e.g. stations KNW, PFO and RDM) a station in the San Jacinto fault zone (station SND) had a moderatet*of 0.035 s and stations in the Imperial Valley usually had highert*s. Generallyt*correlated with average amplification suggesting that sites characterized by low surface velocities and higher attenuation also have more amplification in the 1–6 Hz band. Residuals of peak values were determined by subtracting the prediction of Boore and Atkinson (2008). There is a correlation between average amplification and peak velocity, but not peak acceleration. Interestingly, there is less scatter at high values of amplification although there is also less data. Scatter in values of peak velocity and peak acceleration are higher at shorter compared to longer durations. When using a frequency-dependent form forQ, variances are higher, sometimes much higher; the dataset does not support frequency-dependentQ, which is not similar to results from the Imperial Valley and northeastern North America.

This article describes the first step toward the development of the geophysical model function (GMF) for the retrieval of wind speed and wind stress in hurricanes, based on developing a relation between the cross-polarized satellite SAR data from Sentinel-1 and winds/stress observed from collocated NOAA GPS-dropsondes data. Field measurements and remote sensing data for tropical cyclones in the Atlantic Ocean were analyzed. Using the data measured by GPS-dropsondes, average wind velocity profiles were obtained, while the parameters of the wind boundary layer (drag coefficient and friction velocity) were restored from the “wake” part of the velocity profiles using the self-similarity property. The self-similarity of the velocity profile “defect” in the boundary layer, known from the fluid dynamics, was used to retrieve the parameters of the atmospheric boundary layer (the surface wind velocity, drag coefficient, and friction velocity) from the dropsonde wind velocity profiles in ten major hurricanes. Based on the processing of the measurements in the hurricanes Irma 2017/09/07 and Maria 2017/09/21 and 2017/09/23 at a time close to the time of acquisition of the Sentinel-1 images, the dependencies of the cross-polarized normalized radar cross section on the wind speed and wind friction velocity were obtained and used for constructing the GMFs.

Excess fine sediment (

Ultrasonic velocity is a key shale gas reservoir property, especially in the context of gas production or CO 2 injection for geo-sequestration. This ultrasonic velocity reflects the dynamic elastic properties of the rock, and it thus depends on the fracture morphology, which varies significantly with effective stress. However, the precise relationship between ultrasonic velocity and fractured shale morphology is only poorly understood. We thus measured P- and S-wave velocities of fractured shale in two orthogonal directions and imaged the shale with X-ray micro-computed tomography as a function of applied effective stress; and investigated how fracture morphology, P- and S-wave velocity, Young's modulus, shear velocity and Poisson's ratio are interconnected with effective stress. Clearly, most of the small fractures (the width is around 0.1 mm) closed with increasing effective stress, resulting in a different fracture size distribution, which again had a dramatic effect on the elastic rock properties. Furthermore, with increasing effective stress, P- and S-wave velocities increased significantly, such that the orthogonal waves gave a similar response at 2000 psi effective stress despite significant sample heterogeneity. We conclude that the fracture aperture, direction and network characteristics severely influence wave propagation and thus elastic properties. These results can be used to assess natural fracture networks, monitor fracture development during hydraulic fracturing, and predict fracture closure scenarios during production.

The paper investigates the initiation mechanism of debris flow through the survey with detailed analysis for several field debris flow events. The field investigation shows that the debris flow evolution includes distinct three stages: the soil structure changes and forms slide debris, slide debris mobilizes into debris flow, and the debris flow slips a long distance along the slope. In order to reappear and explain the aforementioned phenomenon existing in the initiation procedure of debris flow, the vane shear rheometer device is developed to test the shear rheology properties of debris source. Subsequently, the shear rheological tests with water drained out are performed utilizing the fine sand as tested material. A series of tests are performed and experimental data are obtained including the shear strain, negative pressure, water content, shear velocity, shear resistance, pore water pressure, and line displacements on the shear surface. Based on the changes of water content and negative pressure, the unsaturated permeability coefficients are obtained to explain the water-free infiltration process in the tests. According to the changes of shear velocity and experimental phenomena, the debris flow evolution is divided into three stages including the antecedent rainfall stage, accelerated initiation stage, and long-distance movement stage, which is similar to the three corresponding stages existing in the filed debris flow events. According to the analysis of test results, the mechanics of the debris flow initiation could be explained as the following: the debris source’s shear strength decreased to the value of yield shear strength, the peak shear strength available during undrained loading of a saturated, contractive, sandy soil, after a long period of antecedent rainfall infiltration. The tiny cracks expended to form connecting crack surfaces in the debris source interior, and then the debris source moves rapidly under the continuous rainfall, indicating the debris flow initiation. During the long-distance movement stage, the particles of debris source on the shear surface rearrange and form a smooth slide surface as the values of water content and pore water pressure increase. Therefore, the increase of water content and the decrease of negative pressure caused the soil shear strength decaying, and that is the major reasons of debris flow initiation. In addition, the other key reason is the particles rearranging on the initiation surfaces. The vane shear rheometer apparatus and corresponding test results have provided a more concrete and rational mechanism interpretation for debris flow initiation.

A three-dimensional shear velocity model for the crust and upper mantle beneath the central United States is presented by inverting Rayleigh wave phase velocities from 20s to 100s periods. These ph...

Ambient seismic noise tomography is a novel, low-impact method for investigating the earth's structure. Although most passive seismic studies focus on structures on crustal scales, there are only a few examples of this technique being applied in a mineral exploration context. In this study, we performed an ambient seismic experiment to ascertain the relationship between the shallow shear wave velocity and mineralized zones in the Erzgebirge in Germany, one of the most important metal provinces in Europe. Late Variscan mineralized greisen and veins occurring in the Geyer-Ehrenfriedersdorf mining district of the Central Erzgebirge were mined from medieval times until the end of the 19th century. These occurrences represent a significant resource for commodities of high economic importance, such as tin, tungsten, zinc, indium, bismuth and lithium. Based on ambient noise data from a dense “LARGE-N” network comprising 400 low-power, short-period seismic stations, we applied an innovative tomographic inversion technique based on Bayesian statistics (transdimensional, hierarchical Monte Carlo search with Markov Chains using a Metropolis/Hastings sampler) to derive a three-dimensional shear wave velocity model. An auxiliary 3D airborne time-domain electromagnetic dataset is used to provide additional insight into the subsurface architecture of the area. The velocity model shows distinct anomalies down to approximately 500 m depth that correspond to known geological features of the study area, such as (a) gneiss intercalations in the mica schist-dominated host rock, imaged by a SW–NE striking low-velocity zone with a moderately steep northerly dip, and (b) a NW-trending strike-slip fault, imaged as a subvertical linear zone cross-cutting and offsetting this low-velocity domain. Similar to the velocity data, the electromagnetic data exhibit north-dipping (high-conductivity) structures in the mica schists, corresponding to the strike and dip of the predominant metamorphic fabric. An unsupervised classification performed on the bivariate 3D dataset yielded nine spatially coherent classes, one of which shows a high correspondence with drilled greisen occurrences in the roof zone of a granite pluton. The relatively high mean shear velocity and resistivity values of this class could be explained by changes in density and composition during greisen formation, as observed in other areas of the Erzgebirge. Our study demonstrates the great potential of the cost-efficient and low-impact ambient noise technology for mineral exploration, especially when combined with other independent geophysical datasets.

Much of our knowledge on deep Earth structure is based on detailed analyses of seismic waveforms that often have small amplitude arrivals on seismograms; therefore, stacking is essential to obtain reliable signals above the noise level. We present a new iterative stacking scheme that incorporates Historical Interstation Pattern Referencing (HIPR) to improve data quality assessment. HIPR involves comparing travel-time and data quality measurements between every station for every recorded event to establish historical patterns, which are then compared to individual measurements. Weights are determined based on the individual interstation measurement differences and their similarity to historical averages, and these weights are then used in our stacking algorithm. This approach not only refines the stacks made from high-quality data but also allows some lower-quality events that may have been dismissed with more traditional stacking approaches to contribute to our study. Our HIPR-based stacking routine is illustrated through an application to core-reflected PcP phases recorded by the Transantarctic Mountains Northern Network to investigate ultra-low velocity zones (ULVZs). We focus on ULVZ structure to the east of New Zealand because this region is well-sampled by our dataset and also coincides with the boundary of the Pacific Large Low Shear Velocity Province (LLSVP), thereby allowing us to further assess possible ULVZ-LLSVP relationships. The HIPR-refined stacks display strong ULVZ evidence, and associated synthetic modeling suggests that the ULVZs in this region are likely associated with compositionally distinct material that has perhaps been swept by mantle convection currents to accumulate along the LLSVP boundary.

The preliminary attempts to develop of the geophysical model function (GMF) for the retrieval of wind speed and wind stress in hurricanes, based on a dependency between the cross-polarized satellite SAR data from Sentinel-1 and wind speed or turbulent stress obtained from collocated NOAA GPS-dropsondes data array. Field measurements in the Atlantic Ocean during hurricane season in the period 2001-2018 were analyzed. Using the data measured by GPSdropsondes, due to the ensemble averaging, mean wind velocity profiles were obtained, and the atmospheric boundary layer parameters drag coefficient and turbulent stress (or friction velocity) were retrieved from the “wake” part of the velocity profiles taking into account a self-similarity property of the velocity profile “defect”. The parameters were retrieved for 25 major hurricanes of categories 4 and 5. The collocation of Sentinel-1 images and GPS-dropsonde data was made for the hurricanes Irma 2017/09/07, Maria 2017/09/21 and 2017/09/23, taking into account the assumption that turbulent boundary layer parameters in the hurricanes remain quasistationary. The dependencies of the cross-polarized normalized radar cross-section (NRCS) on the wind speed and wind friction velocity were obtained, the results were compared to the data for small and moderate winds, represented in [1], a good agreement is demonstrated. In the region of high wind speeds the relation between NRCS and the wind friction velocity becomes ambiguous, it may be explained by the dependency on the hurricane sector.

Long-term observations of the main characteristics of the turbulent atmosphere in the Monin – Obukhov similarity theory were carried out in the urban environment of the Tomsk Academgorodok. A mobile ultrasonic station AMK-03-4, developed to measure the characteristics of turbulent meteorological fields, was used for the measurements. The data obtained in the urban environment are compared with the data of long-term observations in mountainous terrain, in different climatic and geographical regions. Under urban conditions, data were obtained for the turbulent scales of velocity V* (friction velocity) and temperature (friction velocity) and temperature T*, which are important characteristics of the Monin-Obukhov similarity theory. The range of experimentally observed Monin-Obukhov numbers in the positive region, where previously there were no experimental data, has been significantly expanded. The main results of this work include the experimental confirmation of the positions of the similarity theory in the urban atmospheric boundary layer.

The core-mantle boundary (CMB) is the most extreme boundary within the Earth where the liquid, iron-rich outer core interacts with the rocky, silicate mantle. The nature of the lowermost mantle atop the CMB, and its role in mantle dynamics, is not completely understood. Various regional studies have documented significant heterogeneities at different spatial scales. While there is a consensus on the long scale-length structure of the inferred S-wave speed tomograms, there are also notable differences stemming from different imaging methods and datasets. Here we aim to overcome over-smoothing and avoid over-fitting data for the case where the spatial coverage is sparse and the inverse problem ill-posed. Here we present an S-wave tomography model at global scale for the Lowermost Mantle (LM) using the Hierarchical Trans-dimensional Bayesian Inversion (HTDBI) framework, LM-HTDBI. Our HTDBI analysis of ScS-S travel times includes uncertainty, and the complexity of the model is deduced from the data itself through an implicit parameterization of the model space. Our comprehensive resolution estimates indicate that short-scale anomalies are significant and resolvable features of the lowermost mantle regardless of the chosen mantle-model reference to correct the travel times above the D’’ layer. The recovered morphology of the Large-Low-Shear-wave Velocity Provinces (LLSVPs) is complex, featuring small high-velocity patches among low-velocity domains. Instead of two large, unified, and smooth LLSVPs, the newly obtained images suggest that their margins are not uniformly flat.