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Introduction: The properties of the S-bursts observed during the storm on 20-21 June 2022 in frequency band 10-32 MHz by the radio telescope URAN-2 are discussed in this paper. The storm was highly populated with other solar bursts, such as Type III bursts and drift pairs. The occurrence rate of S-bursts was very high reaching 60 bursts per minute. All observed S-bursts were characterized by low fluxes with respect to the background radio emission. Thus special processing methods are used to retrieve spectral properties of the bursts. Some individual "long" S-bursts covered the whole frequency band of the URAN-2 radio telescope from 10 to 32 MHz. Such extended in frequency S-bursts were recorded for the first time. 50 extended S-bursts were selected for the further analysis. Methods: The S-bursts dynamic spectra with time-frequency resolutions of 100 ms and 4 kHz as well as single-frequency profiles were used in the analysis. Due to low S-bursts intensities the drift rates were estimated from the timedifferentiated dynamic spectra, highlighting the tracks of the bursts maxima. Polarization dynamic spectra were used for measuring the degree and sense of the S-bursts circular polarization. Individual S-bursts tracks were used for instant coronal inhomogeneities diagnostics. Mean S-bursts parameters retrieved from the statistical processing of the set of 50 bursts were compared with previously obtained ones. Results: We concluded that by the mean durations, drift rates, frequency extent and the polarization all observed S-bursts could be divided into two separate groups, the "short" and the "long" S-bursts. The power-law index of the drift ratefrequency dependence averaged over all 50 selected bursts was found to be 1.7. It was shown that sources of S-bursts most likely move through the Newkirk corona with the velocities of 0.06-0.08c. The power-law dependence of the "long" S-bursts durations on frequency in frequency band of 12-30 MHz was obtained. Its index equal to -0.61 appeared to be very close to that for Type III bursts. From this dependence the electron velocity dispersion in the beam, responsible for S-bursts generation was calculated. Its value of 0.02 indicates that the beams, responsible for S-bursts generation are almost monoenergetic. Discussion: It is assumed that non-monotonic appearance of individual S-bursts tracks on the dynamic spectrum reflects density inhomogeneities encountered by the sources on their paths. From the dynamic spectra of such S-bursts the characteristic size and amplitude of these coronal inhomogeneities were detected. From the S-bursts durations and the velocities of their sources the longitudinal sizes of the latter were estimated. It was then shown that the sizes of small-scale coronal inhomogeneities were comparable to those of "long" Sbursts sources. Thus we concluded that individual tracks of the "long" S-bursts can be used for fie diagnostics the coronal plasma at heliocentric heights range from 1.7 to 3.2 Rs, where Rs is the solar radius. On the other hand, these tracks being ensemble-averaged give the information about the long-term large scale properties of the corona. [ABSTRACT FROM AUTHOR]

Wave‐induced fluid flow is considered to be a major source of seismic attenuation and dispersion in porous rocks. From the physical description of partially saturated reservoirs, numerous analytical solutions based on upscaling homogenization theories have been employed to calculate equivalent frequency‐dependent poroelastic media. Nevertheless, dispersion and attenuation predictions are often not reasonably consistent with laboratory and field measurements in a broad frequency range, particularly due to influences of biphasic fluids and their distribution, presence of heterogeneities on various length scales, and pore microstructure. We investigate the role of pore microstructure on pressure and fluid saturation dependence of elastic velocities in tight sandstones. Previous work points out that differentiating the impacts of heterogeneities at various scales on dispersion within seismic exploration and sonic frequencies can be very difficult. In practice, this is because fluid‐related dispersion mechanisms are impossible to be independent. Thus, it is important for a theoretical and more quantitative analysis of the relative contribution of interrelated energy dissipation processes through a better understanding of combined influences due to the presence of microscopic and mesoscopic heterogeneities. Based on microscopic squirt flow and mesoscopic flow in a partially saturated medium, we develop a poroelastic model that allows evaluating the overall frequency‐dependent dispersion via considering a random distribution of fluid heterogeneities as well as the broadly distributed aspect ratio of compliant pores. Experimental validation of the model is accomplished via a comprehensive comparison of predictions with measurements of partially saturated velocities versus pressure and fluid for sandstones with specific pore microstructures. [ABSTRACT FROM AUTHOR]

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The Carmelies Theory (CT) was successful in Non–Dark Matter explanation of the rotation curves of galaxies. But is this theory also applicable in extragalactic scales or other fields?. In this article, we used this theory for two specific cases (Galaxy Cluster Mass (GCM) and Globular Cluster Velocity Dispersions) and finally (according to the observational data) they have come to the conclusion that the theory is facing problems in these fields. [ABSTRACT FROM AUTHOR]

The spatial autocorrelation method is an important method for extracting the velocity dispersion curve from microtremor data. However, site data typically cannot strictly meet spatial and temporal stationary feature, and this greatly affects the accuracy of the calculation results of this method. Therefore, based on the cosine similarity theory, this study deduces the applicability of the spatial autocorrelation method to unidirectional Rayleigh surface waves and again verifies the applicability of this method to spatially and temporally stationary Rayleigh waves. The numerical simulation results demonstrate that the velocity dispersion curve can be extracted from a one-way Rayleigh wave using the spatial autocorrelation method to obtain an accurate geological profile, whereas the superposition of finite groups of Rayleigh waves in different directions cannot yield an accurate geological profile. In this study, we quantitatively analyzed the impact of the spatial autocorrelation method on the extraction of the velocity dispersion curve when the signal could not meet the characteristics of temporal and spatial stationarity through numerical simulation. The results reveal that the velocity-dispersion curve can be accurately extracted only when the signal satisfies both spatial and temporal stationarity. When a signal is closer to the spatial and temporal stationary characteristics, this indicates that a more accurate velocity dispersion curve can be extracted. These results provide a reference for improving the calculation accuracy of spatial autocorrelation methods. [ABSTRACT FROM AUTHOR]

Introduction: The properties of the S-bursts observed during the storm on 20–21 June 2022 in frequency band 10–32 MHz by the radio telescope URAN-2 are discussed in this paper. The storm was highly populated with other solar bursts, such as Type III bursts and drift pairs. The occurrence rate of S-bursts was very high reaching 60 bursts per minute. All observed S-bursts were characterized by low fluxes with respect to the background radio emission. Thus special processing methods are used to retrieve spectral properties of the bursts. Some individual “long” S-bursts covered the whole frequency band of the URAN-2 radio telescope from 10 to 32 MHz. Such extended in frequency S-bursts were recorded for the first time. 50 extended S-bursts were selected for the further analysis.Methods: The S-bursts dynamic spectra with time-frequency resolutions of 100 ms and 4 kHz as well as single-frequency profiles were used in the analysis. Due to low S-bursts intensities the drift rates were estimated from the time-differentiated dynamic spectra, highlighting the tracks of the bursts maxima. Polarization dynamic spectra were used for measuring the degree and sense of the S-bursts circular polarization. Individual S-bursts tracks were used for instant coronal inhomogeneities diagnostics. Mean S-bursts parameters retrieved from the statistical processing of the set of 50 bursts were compared with previously obtained ones.Results: We concluded that by the mean durations, drift rates, frequency extent and the polarization all observed S-bursts could be divided into two separate groups, the “short” and the “long” S-bursts. The power-law index of the drift rate-frequency dependence averaged over all 50 selected bursts was found to be 1.7. It was shown that sources of S-bursts most likely move through the Newkirk corona with the velocities of 0.06–0.08c. The power-law dependence of the “long” S-bursts durations on frequency in frequency band of 12–30 MHz was obtained. Its index equal to −0.61 appeared to be very close to that for Type III bursts. From this dependence the electron velocity dispersion in the beam, responsible for S-bursts generation was calculated. Its value of 0.02 indicates that the beams, responsible for S-bursts generation are almost monoenergetic.Discussion: It is assumed that non-monotonic appearance of individual S-bursts tracks on the dynamic spectrum reflects density inhomogeneities encountered by the sources on their paths. From the dynamic spectra of such S-bursts the characteristic size and amplitude of these coronal inhomogeneities were detected. From the S-bursts durations and the velocities of their sources the longitudinal sizes of the latter were estimated. It was then shown that the sizes of small-scale coronal inhomogeneities were comparable to those of “long” S-bursts sources. Thus we concluded that individual tracks of the “long” S-bursts can be used for fie diagnostics the coronal plasma at heliocentric heights range from 1.7 to 3.2 Rs, where Rs is the solar radius. On the other hand, these tracks being ensemble-averaged give the information about the long-term large scale properties of the corona.

We study the anelastic properties (attenuation and velocity dispersion) of surface waves at an interface between a finite water layer and a porous medium described by Biot theory including the frequency-dependent effects due to mesoscopic flow. A closed-form dispersion equation is derived, based on potential functions and open and sealed boundary conditions (BC) at the interface. The analysis indicates the existence of high-order surface modes for both BCs and a slow true surface mode only for sealed BC. The formulation reduces to two particular cases in the absence of water and with infinite-thickness water layer, with the presence of pseudo-versions of Rayleigh and Stoneley waves. The mesoscopic flow affects the propagation of all the pseudo-surface waves, causing significant velocity dispersion and attenuation, whereas the effect of the BC is mainly evident at high frequencies, due to the presence of the slow Biot wave. The mesoscopic-flow peak moves to low frequencies as the thickness of the water layer increases. In all cases, the true surface wave resembles the slow P2 wave, and is hardly affected by the flow. [ABSTRACT FROM AUTHOR]

Heavy oil has high density and viscosity, and exhibits viscoelasticity. Gassmann's theory is not suitable for materials saturated with viscoelastic fluids. Directly applying such model leads to unreliable results for seismic inversion of heavy oil reservoir. To describe the viscoelastic behavior of heavy oil, we modeled the elastic properties of heavy oil with varying viscosity and frequency using the Cole-Cole-Maxwell (CCM) model. Then, we used a CCoherent Potential Approximation (CPA) instead of the Gassmann equations to account for the fluid effect, by extending the single-phase fluid condition to two-phase fluid (heavy oil and water) condition, so that partial saturation of heavy oil can be considered. This rock physics model establishes the relationship between the elastic modulus of reservoir rock and viscosity, frequency and saturation. The viscosity of the heavy oil and the elastic moduli and porosity of typical reservoir rock samples were measured in laboratory, which were used for calibration of the rock physics model. The well-calibrated frequency-variant CPA model was applied to the prediction of the P- and S-wave velocities in the seismic frequency range (1–100 Hz) and the inversion of petrophysical parameters for a heavy oil reservoir. The pre-stack inversion results of elastic parameters are improved compared with those results using the CPA model in the sonic logging frequency (∼10 kHz), or conventional rock physics model such as the Xu-Payne model. In addition, the inversion of the porosity of the reservoir was conducted with the simulated annealing method, and the result fits reasonably well with the logging curve and depicts the location of the heavy oil reservoir on the time slice. The application of the laboratory-calibrated CPA model provides better results with the velocity dispersion correction, suggesting the important role of accurate frequency dependent rock physics models in the seismic prediction of heavy oil reservoirs. [ABSTRACT FROM AUTHOR]

Carbonate rock is a critical reservoir for China's onshore oil and gas exploration. Carbonate reservoirs in different regions significantly differ in sedimentary and diagenesis processes and factors affecting their petrophysical and seismic rock physics properties. Therefore, it is critical to analyze the corresponding properties of carbonate rocks in different regions. Based on systematic petrological, rock microstructure, physical property, and seismic elastic characteristic measurements of deep carbonate reservoir samples in the Tarim Basin, the variation laws and influencing factors of the samples' physical and seismic elastic properties are analyzed. Based on these measurements, the variation patterns and influencing factors of petrophysical and seismic rock properties of rock samples are analyzed. The results show that the carbonate pore structure controls the overall variations of petrophysical and seismic rock physical properties of carbonate samples, and it is challenging to build a simple statistical model of porosity—permeability, porosity—velocity, and density—velocity. P- and S-velocities correlate well, and the P-and S-velocity ratio is a good index for rock typing. For tight carbonate samples, apparent velocity dispersion at a seismic exploration frequency band (5–200 Hz) can be observed, and the pore structure controls the velocity dispersion and attenuation features. Carbonate samples with crack-dissolution pores show moderately stronger velocity dispersion than samples with dissolution and microcrack pores. The pore aspect ratio and the frame flexibility factor (γ) calculated from the seismic rock physics model correlate well with pore structure parameters, such as the characteristic ratio surface. The pore aspect ratio and frame flexibility factor can be used to quantitatively characterize the changes in the pore structure of tight carbonate samples, reflecting the pore structure effects on the elastic wave velocity. This study's results can provide a basis for rock-typing carbonate reservoirs, lithology, and hydrocarbon detection of relevant reservoirs. [ABSTRACT FROM AUTHOR]

The pressure dependence of elastic parameters of rocks is mainly controlled by the geometry of the pore space. In general, the compliant-stiff pore structure model can be used to reasonably describe this pressure dependence. However, our experiment measurements revealed that for tight sandstone rock with complex pore structures, the contribution of the compressibility of the stiff pores to the elastic modulus is significant. The dual porosity is not sufficient to explain the variation of ultrasonic velocity with pressure. For this reason, we adopted a triple pore structure to divide the rock pore space into equant pores, intermediate pores and compliant pores. Our laboratory measurement and model results show that this pore space division can better describe the pressure dependence of the elastic moduli of rocks. The low-frequency stress–strain measurements show that the fluid-saturated tight sandstone has obvious dispersion in the seismic frequency band, which is primarily attributed to the squirt flow effect. In order to study the pressure and frequency dependence of the elastic moduli of tight sandstone, we retrieved the geometric parameters of the pore structure from the pressure variation of the ultrasonic velocities under dry conditions. Based on this complex pore structure and the extension of the squirt flow model, we constructed an elaborate rock physics model to explain the pressure and frequency dependence of velocity. The model does not require adjustable parameters, and all parameters are measured and calculated by the laboratory, which improves the accuracy of theoretical modelling. The modified squirt flow model can be used to describe dispersion and attenuation in a wide frequency band, and fit well with the velocity measurements in both the low-frequency range and the ultrasonic frequency range under different pressures. Therefore, this rock physics model could be applied in the extraction of pore microstructure and fluid properties provided elastic moduli or velocities can be estimated accurately. [ABSTRACT FROM AUTHOR]

At present, a series of petrophysical experimental studies have been carried out on the velocity dispersion and attenuation caused by wave induced fluid flow. So as many valuable theoretical models have been proposed or developed. But these studies fail to reflect the influence of different pore structure types on velocity dispersion and attenuation. Carbonate rocks have complex pore structure and strong heterogeneity. The study of the influence of pore structure on acoustic propagation characteristics at different frequencies is of great significance for further refinement of reservoir prediction. Through computed tomography scan and digital image processing, the pore structure distribution of longitudinal section of carbonate rock is obtained. On this basis, the finite difference numerical simulation of acoustic wave field is carried out, and the variation law of acoustic velocity with frequency and the relationship between acoustic velocity dispersion and attenuation coefficient are analyzed. The acoustic velocity extrapolation model based on frequency dispersion is established and compared with the experimental results to verify the effectiveness. The research results provide a theoretical basis for the prediction of carbonate reservoir parameters. [ABSTRACT FROM AUTHOR]

There is a mathematical analogy between the poroelastic and thermoelastic behavior of the compressional P wave, whose dissipation is due to the coupling between the elastic deformation and the phenomenon of pressure and heat diffusion, represented by Darcy's law and heat conduction, respectively. This attenuation effect is more pronounced in heterogeneous media, where conversion of the fast P wave to the slow (Biot) and thermal diffusive modes occurs at material interfaces. Specifically, the problem is to obtain the P-wave properties of a porous medium due to temperature gradients between the solid and fluid phases. Then, we consider a simplified one-dimensional porous medium and obtain the quality factor, Q, and phase velocity as a a function of frequency, based on an isostress condition and using Gassmann equation and the Kramers Kronig relations.The model allows for the incorporation of a relaxation time to simulate a proper wave-like behavior at high frequencies, avoiding in this way infinite velocities. Moreover, we perform a complete analysis varying the different parameters, namely, the heat conduction, the specific heat, the thermal expansion, the types of solid and fluid and the pore size. [ABSTRACT FROM AUTHOR]

The elastic wave propagating in rock has velocity dispersion characteristic that holds an imperative significance in rock engineering. This paper aims at study elastic wave velocity dispersion characteristic in limestone dynamic fracture process. For this purpose, the experiment of elastic wave propagates in the limestone when cyclic loading and unloading process is conducted, and elastic wave velocity dispersion characteristic is analyzed. Based on multifractal theory and Raiga model, the influence of fracture degree on velocity dispersion characteristic is discussed qualitatively and quantitatively with evolution characteristic of the AE event. The research results indicate that there is velocity dispersion characteristic when elastic wave propagates in the limestone sample, which presents positive correlation between velocity and frequency. The variation of wave velocity dispersion characteristic is consistent with that of AE activities and both of them show a nonlinear increase trend with an increase of loading. The reason for velocity dispersion characteristic is that the retarding effect of microcracks on elastic wave velocity with different frequencies is different, and the effect is enhanced with the microcrack scale increasing. According to the variation of multifractal parameter Δ α of the AE event energy series, the limestone sample under loading experiences a transformation process from small-scale microcrack to large-scale microcrack and small-scale microcrack dominance to multi-scale microcrack coexistence, and this complex transformation process results in nonlinear variation of velocity dispersion characteristic. Further, the multifractal parameter Δ α is introduced into Raiga model to establish the velocity dispersion quantitative model. The model can describe well elastic wave velocity dispersion characteristic, and indicates quantitatively that there is an obvious nonlinear positive correlation between the dispersion characteristic and the fracture degree. The research results have important theoretical and practical significance for understanding elastic wave velocity dispersion characteristic in limestone dynamic fracture process. It can provide important support for characterizing rock fracture process using elastic wave velocity dispersion characteristic. [ABSTRACT FROM AUTHOR]

The existing acoustic logging methods for evaluating the hydraulic fracturing effectiveness usually use the fracture density to evaluate the fracture volume, and the results often cannot accurately reflect the actual productivity. This paper studies the dynamic fluid flow through hydraulic fractures and its effect on borehole acoustic waves. Firstly, based on the fractal characteristics of fractures observed in hydraulic fracturing experiments, a permeability model of complex fracture network is established. Combining the dynamic fluid flow response of the model with the Biot-Rosenbaum theory that describes the acoustic wave propagation in permeable formations, the influence of hydraulic fractures on the velocity dispersion of borehole Stoneley-wave is then calculated and analyzed, whereby a novel hydraulic fracture fluid transport property evaluation method is proposed. The results show that the Stoneley-wave velocity dispersion characteristics caused by complex fractures can be equivalent to those of the plane fracture model, provided that the average permeability of the complex fracture model is equal to the permeability of the plane fracture. In addition, for fractures under high-permeability (fracture width 10~100 μm, permeability ~100 μm2) and reduced permeability (1~10 μm, ~10 μm2 as in fracture closure) conditions, the Stoneley-wave velocity dispersion characteristics are significantly different. The field application shows that this fluid transport property evaluation method is practical to assess the permeability and the connectivity of hydraulic fractures.

The surface-acoustic-wave (SAW) velocity was measured in the frequency range of 400â€"7000 Hz in watermelon and melon to evaluate the firmness nondestructively. We showed that the positive velocity dispersion (velocity increases with increasing frequency) observed was caused by the fruit structure, which consists of a hard pericarp and underlying soft flesh. In watermelon, the low-frequency limit of the velocity dispersion curve observed for the pericarp predicted the SAW velocity in watermelon flesh, which was measured to be independent of frequency. In melon, the positive velocity dispersions observed for the pericarp as well as the flesh suggested a distribution of elasticity in the depth direction. Ripening for fourteen days caused a decrease in the SAW velocity by 34%â€"57% depending on the frequency. The present results demonstrate that the SAW velocity dispersion is a good measure of the firmness and ripening of fruits. [ABSTRACT FROM AUTHOR]

The use of two-station seismic records to calculate phase velocity is a very fast seismic exploration method, but its sensitivity to interference severely limits its applications in engineering. This study investigates the suppression and amplification characteristics of noise disturbances by calculating the velocity dispersion curve, using the spatial autocorrelation method. The results showed that in the first monotonic interval of the correlation coefficient, when the phase velocity with a correlation coefficient close to 1 is calculated, the disturbance of the noise is significantly amplified, and the phase velocity with a correlation coefficient of zero is suppressed. The overall relative error was suppressed in other monotonic intervals. The influence of seismic records with different noise levels and correlation coefficients of different radii on the phase velocity was analyzed as well. By combining the correlation coefficients of different radii and the zero point of the correlation coefficient, one can effectively suppress the noise disturbance, which can ensure the lateral resolution of different depths and widen the detection frequency range. Using this method, we processed the active source data of the pavement that collapsed in the cities of Sichuan province (China). We found that the velocity dispersion curves and velocity profiles obtained using a single radius were only consistent with the local results of the surface wave multichannel analysis calculated using the surface waves method. The results of the multi-radius autocorrelation coefficient combined with the zero-autocorrelation coefficient agreed well with the results of the multi-channel analysis and showed high lateral resolution. [ABSTRACT FROM AUTHOR]

We present a novel coupled fluid‐poroelastic model and an associated numerical upscaling procedure to calculate seismic attenuation and velocity dispersion in porous rocks induced by fluid pressure diffusion (FPD) in the presence of mesoscopic fluid‐saturated voids, such as, for example, vugs or factures. By applying appropriate interface conditions, the proposed model couples the Navier‐Stokes equations for viscous fluids with Biot's equations of poroelasticity to model the mesoscopic voids and the embedding background, respectively. A finite element method is employed to solve the coupled problem for a set of three relaxation tests, which enables us to compute the complex‐valued and frequency‐dependent equivalent stiffness matrix of the considered synthetic sample. The newly proposed fluid‐poroelastic approach is compared with a purely poroelastic one as well as a fluid‐elastic approach in a benchmark model containing interconnected mesoscopic fractures embedded in a poroelastic background. We obtain excellent agreement for the proposed approach and the purely poroelastic model by optimizing the material properties of the fractures for the latter, which demonstrates both the correctness and advantages of our method over the purely poroelastic approach for modeling fluid‐saturated mesoscopic voids. We also observe that, while the coupled fluid‐elastic approach and the proposed method provide consistent results with regard to seismic attenuation due to the fracture‐to‐fracture FPD, the latter also allows to account for the effects of fracture‐to‐background FPD. Finally, we employ the proposed methodology to explore the seismic characteristics of a synthetic "vuggy" carbonate‐type sample, for which we visualize and interpret the resulting seismic attenuation in terms of FPD between the microscopic and mesoscopic pores. Plain Language Summary: Seismic waves are commonly employed to study porous and/or fractured geological formations in the Earth's upper crust. In the presence of relatively small heterogeneities, such as fluid‐saturated fractures or vugs, seismic waves may exhibit velocity variation and amplitude decay due to fluid pressure diffusion processes, which are important characteristics of seismic waves. To date, it remains difficult to understand how complex and fluid‐saturated voids impact these seismic characteristics. To address this problem, we propose a novel coupled fluid‐poroelastic model and develop a corresponding numerical upscaling procedure to calculate seismic characteristics of porous media containing mesoscopic heterogeneities. Our results demonstrate that the proposed approach is more accurate and flexible than previous related models, which, in turn, opens new and interesting perspectives for the seismic exploration of corresponding geological environments. Key Points: We develop a numerical upscaling procedure to calculate seismic signatures based on a novel coupled fluid‐poroelastic modelIn the presence of fluid‐saturated mesoscopic voids, the newly proposed coupled approach is more flexible and more accurate than existing methodologiesApplication to a synthetic "vuggy" carbonate‐type rock sample provides new insights into seismic energy dissipation related to fluid pressure diffusion between microscale and mesoscale pores [ABSTRACT FROM AUTHOR]

The remarkable development of cosmology benefits from the increasingly improved measurements of cosmic distances, including absolute distances and relative distances. In recent years, however, the emerged cosmological tensions have motivated us to explore independent and precise late-universe probes. The two observational effects of strong gravitational lensing (SGL), the velocity dispersions of lens galaxies and the time delays between multiple images can provide measurements of relative and absolute distances, respectively, and their combination makes it possible to break the degeneracies between cosmological parameters and enable tight constraints on them. In this paper, we combine the observed 130 SGL systems with velocity-dispersion measurements and 7 SGL systems with time-delay measurements to constrain dark-energy cosmological models. It is found that the combination of the two effects does not significantly break the degeneracies between cosmological parameters as expected. However, with the simulations of 8000 SGL systems with well-measured velocity dispersions and 55 SGL systems with well-measured time delays based on the forthcoming LSST survey, we find that the combination of two effects can significantly break the parameter degeneracies, and make the constraint precision of cosmological parameters meet the standard of precision cosmology. We conclude that the observations of SGL will become a useful late-universe probe for precisely measuring cosmological parameters. [ABSTRACT FROM AUTHOR]

There are complex heterogeneous entities in the underground medium, and the heterogeneous scale has a substantial impact on wave propagation. In this study, we used a set of 11 samples of glass beads as high-velocity heterogeneous bodies to evaluate the impact of such heterogeneous bodies on the propagation of P-wave. We vary the heterogeneous scale by changing the diameter of the glass beads from 0.18 to 11 mm while keeping the same volume proportion (10%) of the beads for the set of 11 samples. The pulse transmission method was used to record measurements at the ultrasonic frequencies of 0.34, 0.61, and 0.84 MHz in the homogeneous matrix. The relationship between P-wave field features and heterogeneity scale, P-wave velocity, and the multiple of the wave number and heterogeneous scale (ka) was observed in the laboratory, which has sparked widespread interest and research. Heterogeneous scale affects P-wave propagation, and its wave field changes are complex. The waveform, amplitude, and velocity of the recorded P-waves correlate with the heterogeneous scale. For the forward scattering while large-scale heterogeneities, noticeable direct and diffracted waves are observed in the laboratory, which indicates that the influence of direct and diffracted waves cannot be ignored for large-scale heterogeneities. The relationship between velocity and ka shows frequency dependence; the reason is that the magnitude of change in velocity caused by wave number is different from that caused by heterogeneous scale. According to the change in the recorded waveform, amplitude variation, or the relationship between the velocity measured at different frequencies and the heterogeneous scale, the identified turning points of the ray approximation are all around ka = 10. When ka is less than 1, the velocity changes slowly and gradually approaches the effective medium velocity. The ray velocity measured for heterogeneous media with large velocity perturbations in the laboratory is significantly smaller than the velocity predicted by the perturbation theory. [ABSTRACT FROM AUTHOR]

One of the main objectives in the hydrocarbon reservoir characterization is determining rock and fluid properties that rely extensively on inference from seismic observations. In this letter, we present a novel Bayesian prestack inversion method using frequency-dependent amplitude versus offset (AVO) analysis with the goal to directly estimate gas saturation and porosity of a target thin reservoir zone. The proposed methodology is based on an improved Markov chain Monte Carlo (MCMC) sampling algorithm, which is computationally very coefficient due to its satisfactory acceptance probability and the convergence speed of Markov chains. Using a nonlinear rock physics model (RPM), properly calibrated for the investigating area, and a seismic forward operator based on the frequency-domain propagator matrix approach in the Bayesian inversion framework, we then evaluate the full posterior probability distribution of petrophysical parameters conditioned to seismic data and available prior information, using the MCMC algorithm in which we iteratively sample within the petrophysical property space. The proposed inversion approach is validated through applications to a synthetic reservoir model and the real seismic data from gas-bearing reservoirs with strong velocity dispersion. [ABSTRACT FROM AUTHOR]

Fluctuations of gravitational forces cause so-called Newtonian noise (NN) in gravitational-wave detectors which is expected to limit their low-frequency sensitivity in upcoming observing runs. Seismic NN is produced by seismic waves passing near a detector’s suspended test masses. It is predicted to be the strongest contribution to NN. Modeling this contribution accurately is a major challenge. Arrays of seismometers were deployed at the Virgo site to characterize the seismic field near the four test masses. In this paper, we present results of a spectral analysis of the array data from one of Virgo’s end buildings to identify dominant modes of the seismic field. Some of the modes can be associated with known seismic sources. Analyzing the modes over a range of frequencies, we provide a dispersion curve of Rayleigh waves. We find that the Rayleigh speed in the NN frequency band 10â€"20 Hz is very low (≲100 m sâˆ'1), which has important consequences for Virgo’s seismic NN. Using the new speed estimate, we find that the recess formed under the suspended test masses by a basement level at the end buildings leads to a 10 fold reduction of seismic NN. [ABSTRACT FROM AUTHOR]

Patchy saturation of gas and brine within the porous rock can induce significant attenuation and velocity dispersion effects, which in turn have a profound impact on seismic data. Thus, there should be a close relationship between dispersion and reservoir parameters, such as saturation, porosity, and permeability. Hence, using seismic data to determine dispersion information has been the subject of intensive research in recent years. It can help quantitatively predicting gas saturation and monitoring CO2 sequestration, a key strategy for mitigation of global warming. Here, a frequency-dependent prestack waveform inversion workflow was proposed to extract the wave-induced fluid flow (WIFF) effect from seismic data (WIFF prestack waveform inversion strategy). The proposed approach consists of three essential parts, comprising spectral decomposition, $Q$ -compensated prestack waveform inversion, and frequency-dependent prestack waveform inversion. First, $\ell _{1}$ norm constrained inverse spectral decomposition is exploited to provide time-frequency amplitude and phase spectra with high resolution and reliable accuracy. Then, constant- $Q$ compensated prestack waveform inversion is used to generate relatively precise $P$ - and $S$ -wave velocities, density, and Fréchet derivative for the subsequent dispersion inversion. Finally, frequency-divided seismic data and the estimated parameters and Fréchet derivative are used to invert the $P$ -wave velocity dispersion. A comparison between the inversion results and band-limited rock physics analysis results shows that the proposed method can provide a quantitative inversion of the velocity dispersion to some extent. The proposed strategy provides a possibility for quantifying dispersion and further estimating gas saturation. [ABSTRACT FROM AUTHOR]

Natural gas hydrates have the properties of ice with a microporous structure and its concentration in sediments highly affects the wave velocity and attenuation. Previous studies have performed investigations based on the measurements of laboratory data, sonic-log data, and field data, whereas the variation trend of wave dissipation with increasing hydrate concentration at different frequencies is still unclear. We consider two different models to study this problem, both based on the Biot-Rayleigh double-porosity theory. In the first model, hydrate is part of the pore infill, unbonded from the grains, and brine saturates the remaining pore space. In the second model, hydrate forms a second skeleton and cements the grains. We obtain the P-wave velocity dispersion and attenuation as a function of the inclusion radius, porosity, and hydrate content. The analysis shows that the predictions of both models agree with the experimental data. At sonic log frequencies, the second model predicts much more attenuation, due to wave-induced local fluid flow (mesoscopic loss), and the behavior is such that below a given hydrate concentration the dissipation increases and then decreases beyond that concentration.

The vitreous humour plays an important role in shock absorption, i.e. the damping of the mechanical movement, to protect the delicate tissues within the eye. However, this damping is different for movements with different frequencies/velocities. While the collective low-frequency (below 100 Hz) damping behaviour of the vitreous humour associated with the saccadic and lens movements is well-studied, to the best of our knowledge, the high-frequency damping behaviour of the vitreous humour, which represents the response of the microstructural components, is not exhaustively documented. Here, we utilise a non-destructive testing method called Optical Coherence Tomography (OCT) to measure the high-frequency (100–350 Hz, waves able to probe approximately 500 µm distances) biomechanical behaviour of the vitreous humour. We parametrise this behaviour by calculating the shear storage modulus, shear loss modulus and phase angle. We compare these parameters to their low-frequency counterparts obtained with a rheometer, providing a comprehensive mechanical spectrum of the vitreous humour behaviour. The processing method developed in this study and the data collected help better understand the vitreous humour shock absorption properties. Consequently, they could allow a development of better vitreous humour substitutes. The local probing of the high-frequency regime and the non-invasive character of the OCT method provide new qualities in mapping the damping behaviour. [ABSTRACT FROM AUTHOR]

The remarkable development of cosmology benefits from the increasingly improved measurements of cosmic distances, including absolute distances and relative distances. In recent years, however, the emerged cosmological tensions have motivated us to explore independent and precise late-universe probes. The two observational effects of strong gravitational lensing (SGL), the velocity dispersions of lens galaxies and the time delays between multiple images can provide measurements of relative and absolute distances, respectively, and their combination makes it possible to break the degeneracies between cosmological parameters and enable tight constraints on them. In this paper, we combine the observed 130 SGL systems with velocity-dispersion measurements and 7 SGL systems with time-delay measurements to constrain dark-energy cosmological models. It is found that the combination of the two effects does not significantly break the degeneracies between cosmological parameters as expected. However, with the simulations of 8000 SGL systems with well-measured velocity dispersions and 55 SGL systems with well-measured time delays based on the forthcoming LSST survey, we find that the combination of two effects can significantly break the parameter degeneracies, and make the constraint precision of cosmological parameters meet the standard of precision cosmology. We conclude that the observations of SGL will become a useful late-universe probe for precisely measuring cosmological parameters.

Strong scaling relations between host galaxy properties (such as stellar mass, bulge mass, luminosity, effective radius etc) and their nuclear supermassive black hole's mass point toward a close co-evolution. In this work, we first review previous efforts supporting the fundamental importance of the relation between supermassive black hole mass and stellar velocity dispersion (MBH-σe). We then present further original work supporting this claim via analysis of residuals and principal component analysis applied to some among the latest compilations of local galaxy samples with dynamically measured supermassive black hole masses. We conclude with a review on the main physical scenarios in favor of the existence of a MBH-σe relation, with a focus on momentum-driven outflows.

Modeling the scattering-induced attenuation of elastic waves in heterogeneous polycrystals has practical applications in seismology and non-destructive evaluation. However, attenuation modeling for polycrystals with preferred crystallographic orientation (statistically anisotropic or textured polycrystals) has not been well studied. The far-field approximation (FFA) model, which is applicable for arbitrary crystal (triclinic) symmetry and valid for the whole frequency range (Rayleigh region, stochastic regime, and geometric region), has been reported for texture-free polycrystalline materials. This paper extends the FFA model to textured polycrystals with ellipsoidal grains of arbitrary crystal symmetry. This FFA model for textured polycrystals encompasses two advantages: a simple form of dispersion equation and high computational efficiency. Furthermore, this FFA model can predict both the attenuation and phase velocity of elastic waves in textured polycrystals. The FFA model in this study has also been validated by comparison with the full-wave second-order attenuation model on textured polycrystals of triclinic grains. This work provides a simple and efficient tool to predict the elastic wave behavior in heterogeneous polycrystalline materials. [ABSTRACT FROM AUTHOR]

Abstract—A technique is proposed for joint inversion of the surface-wave velocity dispersion data from long travelpaths and the results of the receiver function method. The technique is based on a modification of a surface-wave tomography procedure and allows for the use of the data not only from travelpaths but also obtained at individual isolated points. Initially, the data are reduced to a single type: either to surface wave velocity by calculating the dispersion curve from the vertical velocity section obtained by the receiver function method or to shear wave velocity by one-dimensional inversion of surface-wave dispersion curves from travelpaths. Thus, from the computational point of view, the problem reduces to the following one: to obtain a smoothed estimate of a two-dimensional function from the values ​​of this function at individual points and its average values along lines (travelpaths) which can be considered as straight. A direct application of a surface-wave tomography procedure under the assumption that the points are lines of zero length is impossible because the solution turns out to be singular at the points. To get rid of this obstacle, it is proposed to replace the points by circles of a small radius surrounding these points. Then, the problem of tomography is generalized by using data not only from linear travelpaths, but also from circular travelpaths. A numerical study has shown that an addition of point data results in an increase in the resolution. [ABSTRACT FROM AUTHOR]

Horizontal-to-Vertical Spectral Ratios (HVSR) and Rayleigh group velocity dispersion curves (DC) can be used to estimate the shallow S-wave velocity (VS) structure. Knowing the VS structure is important for geophysical data interpretation either in order to better constrain data inversions for P-wave velocity (VP) structures such as travel time tomography or full waveform inversions or to directly study the VS structure for geo-engineering purposes (e.g., ground motion prediction). The joint inversion of HVSR and dispersion data for 1D VS structure allows characterising the uppermost crust and near surface, where the HVSR data (0.03 to 10s) are most sensitive while the dispersion data (1 to 30s) constrain the deeper model which would, otherwise, add complexity to the HVSR data inversion and adversely affect its convergence. During a large-scale experiment, 197 three-component short-period stations, 41 broad band instruments and 190 geophones were continuously operated for 6 months (April to October 2017) covering an area of approximately 1500km2 with a site spacing of approximately 1 to 3km. Joint inversion of HVSR and DC allowed estimating VS and, to some extent density, down to depths of around 1000m. Broadband and short period instruments performed statistically better than geophone nodes due to the latter’s gap in sensitivity between HVSR and DC. It may be possible to use HVSR data in a joint inversion with DC, increasing resolution for the shallower layers and/or alleviating the absence of short period DC data, which may be harder to obtain. By including HVSR to DC inversions, confidence improvements of two to three times for layers above 300m were achieved. Furthermore, HVSR/DC joint inversion may be useful to generate initial models for 3D tomographic inversions in large scale deployments. Lastly, the joint inversion of HVSR and DC data can be sensitive to density but this sensitivity is situational and depends strongly on the other inversion parameters, namely VS and VP. Density estimates from a HVSR/DC joint inversion should be treated with care, while some subsurface structures may be sensitive, others are clearly not. Inclusion of gravity inversion to HVSR/DC joint inversion may be possible and prove useful.