Reservoir monitoring is essential to guarantee safe operations for all activities involving the production and injection of fluids into the subsurface, such as hydrocarbon production, gas storage and ...the exploitation of geothermal reservoirs. For this purpose, microseismic monitoring networks are operated in real time in order to identify and locate any possible seismic events in the vicinity of the reservoir. The goal of this study is to investigate whether the large amount of ambient seismic noise recorded by seismic reservoir monitoring networks can be used to infer a one‐dimensional shear‐wave velocity profile representative of the area covered by the network. Shear‐wave velocities are generally difficult to characterize and constrain, yet they are key to precisely locate seismic events. The adopted workflow consists of three steps: first, the cross‐correlation functions between all station pairs are retrieved, using 1 year of continuous data; second, the average group‐ and phase velocity dispersion curves are extracted; third, a joint group and phase velocity inversion is done. For validation, the obtained average shear‐wave velocity profile is compared with a regional model of the area as well as with local shear‐wave velocity measurements from a sonic log.
Dense hydrous magnesium silicate (DHMS) phase E is a potential water carrier in subducting slabs that can transport water to the Earth's deep mantle between the bottom of the upper mantle and the ...uppermost transition zone. Therefore, knowledge on the high pressure‒temperature (P‒T) full elastic moduli of phase E at relevant mantle conditions is important in deciphering the existence of DHMS phases and their influences on seismic profiles in the region; however, the high P‒T elasticity data of phase E still remains lacking. In this work, we determined the combined effect of P‒T on the single‐crystal elasticity of phase E up to 24 GPa and 900 K by in situ X‐ray diffraction and Brillouin scattering measurements in externally‐heated diamond anvil cells. The aggregate elastic moduli and compressional‐wave (VP) and shear‐wave (VS) velocities of phase E are then derived by analyzing the single‐crystal elasticity and density data using the third‐order finite‐strain equations. We found that phase E exhibits much lower bulk and shear moduli and acoustic velocities than the most abundant constituent minerals in the upper mantle and transition zone, such as olivine, clinopyroxene, garnet, and wadsleyite. The modeled results using the obtained elasticity results show that the existence of phase E in a hydrated pyrolite model can result in relatively lower Vp and Vs profiles and negative velocity anomalies in seismic observations. The existence of phase E with relatively lower velocity profiles could be a possible origin of the low‐velocity layers atop the 410‐km discontinuity in some cold and highly‐hydrated regions.
Plain Language Summary
Deep‐mantle water storage and circulation remains one of the most intriguing issues in geoscience. Serpentine and its high pressure‒temperature (P‒T) phases, namely high‐density magnesium silicates (phases A, superhydrous B, D, E, and H), are considered to be the dominant potential water carriers in subduction zones. Hence, their sound velocities and density at high P‒T conditions are of particular importance for interpreting seismic observations and understanding water circulation and geodynamic processes in subduction‐related environments. In this study, we report new experimental results on the high P‒T single‐crystal elasticity of phase E up to 24 GPa and 900 K obtained by in situ synchrotron X‐ray diffraction and Brillouin scattering measurements. The single‐crystal elasticity data of phase E are used to derive its aggregate sound velocities and build mantle velocity profiles for dry and hydrated pyrolite models. We found that the existence of phase E in a hydrated pyrolite model can result in relatively lower compressional‐wave and shear‐wave velocity profiles and negative velocity anomalies in seismic observations. This finding helps explain the origin of the low‐velocity layers atop the 410‐km discontinuity in some highly‐hydrated regions.
Key Points
Single‐crystal elasticity of the Mg‐endmember phase E has been measured at high pressure and temperature conditions
The aggregate sound velocities of phase E are much lower than those of the typical minerals in the upper mantle and mantle transition zone
The existence of phase E could contribute to the origin of the low‐velocity layers atop the 410 km discontinuity in some hydrated regions
Estimating river discharge requires simultaneous measurement of velocity and flow depth. While surface velocities are relatively easy to measure using noncontact techniques, depth measurement usually ...requires physically intrusive instrumentation. This limits our capability to remotely monitor discharge in natural rivers subject to bed level variations. This work tests the potential to estimate the surface velocity, the water depth, the depth average velocity, and then discharge of a river using only a sequence of images of the dynamic water surface. The method is based on a comparison between the spatiotemporal Fourier spectra of the pixel intensities of these images and the theoretical dispersion relations of turbulence‐generated surface fluctuations and gravity‐capillary waves. The method is validated through the analysis of water surface videos obtained with fixed cameras from two river sections equipped with conventional discharge gauging. The applicability of the approach is demonstrated and the measurement uncertainties are quantified. The method is affected by two main sources of uncertainty: one derives from the estimation of the velocity index and the other from the obtainable resolution of the Fourier analysis. This resolution strongly controls the observation of depth and/or velocity variations in space and in time. The technique has advantages over current approaches: it has clear physical foundations; the equipment is low cost and is highly mobile; it does not need artificial tracers or physical equipment to measure depth; and it can directly provide estimates of the key flow parameters just from time series of images of the water surface.
Plain Language Summary
Continuous river flow discharge measurement is of great importance for managing natural water resources and flood risks. Current remote measurements that can be performed without immersing sensors only determine the velocity of the very upper surface layer of the river. River water surfaces have distinct patterns of waves. This work demonstrates that by remotely observing the dynamics of water surface waves using a low‐cost video camera and using wave theory, it is possible to estimate the surface water velocity, water depth, depth‐average velocity, and therefore the flow rate.
Key Points
Water surface fluctuations of a river surface react systematically to changes in the flow depth and velocity
Depth, velocity, and discharge are estimated remotely by fitting theoretical relations to the spectra of images of the water surface
The uncertainty of the estimates is governed by the size of river surface covered by the images, limiting the achievable spatial resolution
We argue that comparison with observations of theoretical models for the velocity distribution of pulsars must be done directly with the observed quantities, that is parallax and the two components ...of proper motion. We have developed a formalism to do so, and applied it to pulsars with accurate VLBI measurements. For computational convenience, we model the data with Maxwellians. We find that a distribution with two Maxwellians improves significantly on a single Maxwellian. The “mixed” model takes into account that pulsars move away from their place of birth, a narrow region around the Galactic plane. The best model has 42% of the pulsars in a Maxwellian with average velocity \hbox{$\sigma\sqrt{8/\pi}=120$}σ8/π=120 km s-1, and 58% in a Maxwellian with average velocity 540 km s-1. About 5% of the pulsars has a velocity at birth less than 60 km s-1. For the youngest pulsars (τc < 10 Myr), these numbers are 32% with 130 km s-1, 68% with 520 km s-1, and 3%, with appreciable uncertainties. Our analysis shows that the velocity distribution is wider than can be described with a single Maxwellian; it does not prove that two Maxwellians provide a better description than other wide models.
Seafloor geodetic positioning is crucial for evaluating the marine geodetic network and monitoring various marine activities. We propose a sound velocity correction method based on the precise ...round-trip acoustic positioning model to improve the accuracy of seafloor geodetic positioning. The proposed method models the sound velocity error related to sound velocity profile (SVP) deviation and time-varying error and reduces the propagation error of the acoustic rays in the ocean. The SVP deviation and seafloor position parameters are resolved simultaneously by the Bayesian estimation using the round-trip acoustic travel time. The time-varying errors of SVP are corrected through symbolic regression using multi-gene genetic programming (MGGP) even without any accurate pre-specified mathematical form of marine environmental variations. The results from sea trial conducted in the South China Sea at a depth of 3000 m demonstrate that the developed method compensates for the sound velocity errors and improves the positioning precision of the seafloor transponder, with the position difference between different data sets better than 46.12 cm, the standard deviation of acoustic time residuals better than 0.15 ms, and the square root of the variance of the position better than 0.41 cm.
Single‐crystal elasticity of both α‐ and β‐orthopyroxene was determined up to 20 GPa and 300 K by Brillouin scattering. Using the derived full elastic moduli (Cij), we investigated the contribution ...of the metastable pyroxene to the seismically observed 3%–5% low‐velocity anomalies along the subducting slab in the top transition zone. Our modeled results show that a harzburgite wedge with a 1000‐K colder geotherm and metastable α‐orthopyroxene and olivine displays compressional (VP) and shear‐wave (VS) velocities 3.0%–3.6(6)% and 2.0%–2.8(6)% lower than the surrounding mantle at 410–460 km depth, respectively. At deeper depth up to 520 km, VP and VS of this metastable wedge with β‐orthopyroxene and olivine are 3.6%–4.4(6)% and 2.8%–4.3(6)% lower than the pyrolitic mantle, respectively. The presence of both metastable orthopyroxene and olivine instead of metastable olivine alone helps better explain the origin of the low‐velocity anomalies within the subduction slab in the top transition zone.
Plain Language Summary
Subducting slab plays a significant role in transportation the surface material to the Earth's deep interior. It is normally imaged as a high‐velocity body compared to the surrounding mantle. However, seismic studies detected the existence of 3%–5% low compressional‐wave velocity anomalies accompanied with strong seismic shear‐wave anisotropies within the subducting slab at the top transition zone in various locations of the Earth which cannot be explained by the presence of metastable olivine alone. Besides olivine, orthopyroxene could also remain metastable in the coldest harzburgite layer of the slab. Here we report experimental results on the single‐crystal elasticity of both α‐ and β‐orthopyroxene up to 20 GPa and 300 K. These experimental results allow us to provide a comprehensive evaluation on the velocity profiles of the coldest harzburgite layer of the slab. We found that the coldest harzburgite layer with 22–37 vol.% orthopyroxene and 62–78 vol.% olivine has the VP and VS 3.0%–4.4(6)% and 2.0%–4.5(6)% lower than those of the pyrolitic mantle in the mantle transition zone, respectively. The observed 3%–5% low‐velocity anomalies within the slab in the top transition zone should be explained by the metastable orthopyroxene and olivine instead of metastable olivine alone.
Key Points
Single‐crystal elasticity of α‐ and β‐orthopyroxene was determined to 20 GPa and shows anomalous change across the phase transition
The obtained results were used to model the velocity profiles of the coldest harzburgite layer of the sinking subduction slab
We find that the low‐velocity anomalies within the slab at the top transition zone should be caused by metastable orthopyroxene and olivine
The Reliability of Individualized Load-Velocity Profiles Banyard, Harry G; Nosaka, Kazunori; Vernon, Alex D ...
International journal of sports physiology and performance,
2018-Jul-01, Letnik:
13, Številka:
6
Journal Article
Recenzirano
To examine the reliability of peak velocity (PV), mean propulsive velocity (MPV), and mean velocity (MV) in the development of load-velocity profiles (LVP) in the full-depth free-weight back squat ...performed with maximal concentric effort.
Eighteen resistance-trained men performed a baseline 1-repetition maximum (1-RM) back-squat trial and 3 subsequent 1-RM trials used for reliability analyses, with 48-h intervals between trials. 1-RM trials comprised lifts from 6 relative loads including 20%, 40%, 60%, 80%, 90%, and 100% 1-RM. Individualized LVPs for PV, MPV, or MV were derived from loads that were highly reliable based on the following criteria: intraclass correlation coefficient (ICC) >.70, coefficient of variation (CV) ≤10%, and Cohen d effect size (ES) <0.60.
PV was highly reliable at all 6 loads. MPV and MV were highly reliable at 20%, 40%, 60%, 80%, and 90% but not 100% 1-RM (MPV: ICC = .66, CV = 18.0%, ES = 0.10, SEM = 0.04 m·s
; MV: ICC = .55, CV = 19.4%, ES = 0.08, SEM = 0.04 m·s
). When considering the reliable ranges, almost perfect correlations were observed for LVPs derived from PV
(r = .91-.93), MPV
(r = .92-.94), and MV
(r = .94-.95). Furthermore, the LVPs were not significantly different (P > .05) between trials or movement velocities or between linear regression versus 2nd-order polynomial fits.
PV
, MPV
, and MV
are reliable and can be utilized to develop LVPs using linear regression. Conceptually, LVPs can be used to monitor changes in movement velocity and employed as a method for adjusting sessional training loads according to daily readiness.
Microwave Doppler radar has been used to make noncontact river flow measurements and offers a high resolution and a wide range. However, discharge estimation with microwave Doppler radar is ...challenging due to the inability to measure flow velocity below the river surface based on the Doppler shift. To address this problem, a velocity distribution inversion method based on the Reynolds-Averaged Navier-Stokes (RANS) equations is proposed. A classical two-region model which divides the flow into the inner region and the outer region is applied. Velocity at the inner-outer boundary is estimated using surface velocity and the log law is used to estimate velocity distribution of the inner region. Taking velocities at the surface and the inner-outer boundary as boundary conditions, the velocity distribution in the outer region is derived by solving the RANS equations. Discharge is calculated by combining the proposed method with the velocity-area method. The results illustrated that the velocity distribution obtained by the proposed method and measured by an acoustic instrument are in reasonable agreement. Discharge estimated using the obtained velocity distribution has an error less than 10%. The work indicates the potential of microwave Doppler radar to retrieve the river cross section velocity distribution and estimate discharge.
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