We conducted in situ high‐pressure acoustic‐wave velocity measurements of Fe2+‐bearing MgSiO3 glass up to 158 GPa by Brillouin scattering spectroscopy to clarify the effect of iron on the elasticity ...and structural evolution of silicate melts in the lower mantle. The change in trend of the VS profile, likely induced by the structural transition of Si‐O coordination number from 6 to 6+ proposed in previous studies of silicate glasses, was confirmed to be located at ∼106 GPa. Given the iron contents of partial melts derived from a pyrolitic or chondritic mantle, the transition pressure would be at around 84–97 GPa, which is well within the lowermost‐mantle pressure regime. Our data show the substitution of 12 mol% Fe in MgSiO3 glass decreases the VS by ∼5.5%. This implies that iron affects the buoyancy relations between melts/crystals and the melts at the lowermost mantle will have the higher coordination number than 6.
Plain Language Summary
The physical property of silicate glasses under high‐pressures gives a clue to understand the nature of silicate melts possibly at the bottom of the Earth's mantle because silicate glasses have been considered as good analogs of silicate melts. According to our acoustic wave velocity measurements of Fe2+‐bearing MgSiO3 glass up to 158 GPa, we find the acoustic wave velocity in MgSiO3 glass decreases by ∼5.5% when it contains 12 mol% FeO. In addition, we observe the anomalous increase in the acoustic‐wave velocity profile at 106 GPa, which can be explained by the structural transition in Si‐O coordination number higher than 6. Our results imply that the possible melts at the bottom of the mantle have a denser structure.
Key Points
We have conducted the acoustic wave velocity measurements of Fe2+‐bearing MgSiO3 glass up to 158 GPa
The change in trend of the VS profile, likely induced by the structural transition in Si‐O coordination number, is observed around 106 GPa
Our data show the substitution of 12 mol% Fe in MgSiO3 glass decreases the VS by ∼5.5%
River discharge is an important variable to measure in order to predict droughts and flood occurrences. Once the cross-sectional geometry of the river is known, discharge can be inferred from water ...level and surface flow velocity measurements. Since river discharges are of particular interest during extreme weather events, when river sites cannot be safely accessed, noncontact sensing technologies are particularly appealing. To this purpose, this work proposes a prototype of a low-cost continuous wave (CW) Doppler radar sensor, which is able to monitor the surface flow velocity of rivers. The prototype is tested at two gauged sites in central Italy, along the Tiber River. The surface flow velocity distribution across the river is monitored by means of the analysis of received Doppler signal. The surface velocity statistics are then extracted using a novel algorithm that is optimized to run on a microprocessor platform with minimal computing power (ArduinoUNO). In particular, the radar measurements are used to initialize a 2-D entropy-based velocity model (EVM) that is able to estimate river discharges in any flow condition. Finally, the results concerning the observed discharge provided by the EVM prove to be comparable with those obtained with more expensive commercial solutions. The results are important since the described methodology can be extended to small-size Doppler radar sensors onboard unmanned aerial vehicles (UAVs), the latter providing a method for mapping surface velocity of rivers.
Background
Carotid‐femoral pulse‐wave velocity (cf‐PWV) and brachial‐ankle PWV (ba‐PWV) are the 2 most frequently applied PWV measurements. However, little is known about the comparison of ...hypertensive target organ damage (TOD) with cf‐PWV and ba‐PWV.
Methods and Results
A total of 1599 community‐dwelling elderly subjects (age >65 years) in northern Shanghai were recruited from June 2014 to August 2015. Both cf‐PWV and ba‐PWV were measured using SphygmoCor and VP1000 systems, respectively. Within the framework of comprehensive cardiovascular examinations, risk factors were assessed, and asymptomatic TOD, including left ventricular mass index, peak transmitral pulsed Doppler velocity/early diastolic tissue Doppler velocity (E/Ea), carotid intima‐media thickness, arterial plaque, creatinine clearance rate, and urinary albumin‐creatinine ratio were all evaluated. Both PWVs were significantly associated with male sex, age, waist/hip circumference, fasting plasma glucose, and systolic blood pressure, and ba‐PWV was also significantly related to body mass index. Both PWVs were significantly correlated with most TOD. When cf‐PWV and ba‐PWV were both or separately put into the stepwise linear regression model together with cardiovascular risk factors and treatment, only cf‐PWV, but not ba‐PWV, was significantly associated with carotid intima‐media thickness and creatinine clearance rate (P<0.05). When cf‐PWV and ba‐PWV were both or separately put into the same full‐mode model after adjustment for confounders, only cf‐PWV, but not ba‐PWV, showed significant association with carotid intima‐media thickness and creatinine clearance rate (P<0.05). Similar results were observed in logistic regression analysis.
Conclusions
Taken together, in the community‐dwelling elderly Chinese, cf‐PWV seems to be more closely associated with hypertensive TOD, especially vascular and renal TOD, as compared with ba‐PWV.
Clinical Trial Registration
URL: http://www.clinicaltrials.gov. Unique identifier: NCT02368938.
Southeastern Tibet, which has complex topography and strong tectonic activity, is an important area for studying the subsurface deformation of the Tibetan Plateau. Through the two-station method on ...10-year teleseismic Rayleigh wave data from 132 permanent stations in the southeastern Tibetan Plateau, which incorporates ambient noise data, we obtain the interstation phase velocity dispersion data in the period range of 5–150 s. Then, we invert for the shear wave velocity of the crust and upper mantle through the direct 3-D inversion method. We find two low-velocity belts in the mid-lower crust. One belt is mainly in the SongPan-GangZi block and northwestern part of the Chuan-Dian diamond block, whereas the other belt is mainly in the Xiaojiang fault zone and its eastern part, the Yunnan-Guizhou Plateau. The low-velocity belt in the Xiaojiang fault zone is likely caused by plastic deformation or partial melting of felsic rocks due to crustal thickening. Moreover, the significant positive radial anisotropy (
V
SH
>
V
SV
) around the Xiaojiang fault zone further enhances the amplitude of low velocity anomaly in our
V
SV
model. This crustal low-velocity zone also extends southward across the Red River fault and farther to northern Vietnam, which may be closely related to heat sources in the upper mantle. The two low-velocity belts are separated by a high-velocity zone near the Anninghe-Zemuhe fault system, which is exactly in the inner and intermediate zones of the Emeishan large igneous province (ELIP). We find an obvious high-velocity body situated in the crust of the inner zone of the ELIP, which may represent maficultramafic material that remained in the crust when the ELIP formed. In the upper mantle, there is a large-scale low-velocity anomaly in the Indochina and South China blocks south of the Red River fault. The low-velocity anomaly gradually extends northward along the Xiaojiang fault zone into the Yangtze Craton as depth increases. Through our velocity model, we think that southeastern Tibet is undergoing three different tectonic modes at the same time: (1) the upper crust is rigid, and as a result, the tectonic mode is mainly rigid block extrusion controlled by large strike-slip faults; (2) the viscoplastic materials in the middle-lower crust, separated by rigid materials related to the ELIP, migrate plastically southward under the control of the regional stress field and fault systems; and (3) the upper mantle south of the Red River fault is mainly controlled by large-scale asthenospheric upwelling and may be closely related to lithospheric delamination and the eastward subduction and retreat of the Indian plate beneath Burma.
An InSAR‐GNSS Velocity Field for Iran Watson, Andrew R.; Elliott, John R.; Lazecký, Milan ...
Geophysical research letters,
28 May 2024, Letnik:
51, Številka:
10
Journal Article
Recenzirano
Odprti dostop
We present average ground‐surface velocities and strain rates for the 1.7 million km2 area of Iran, from the joint inversion of InSAR‐derived displacements and GNSS data. We generate interferograms ...from 7 years of Sentinel‐1 radar acquisitions, correct for tropospheric noise using the GACOS system, estimate average velocities using LiCSBAS time‐series analysis, tie this into a Eurasia‐fixed reference frame, and perform a decomposition to estimate East and Vertical velocities at 500 m spacing. Our InSAR‐GNSS velocity fields reveal predominantly diffuse crustal deformation, with localized interseismic strain accumulation along the North Tabriz, Main Kopet Dagh, Main Recent, Sharoud, and Doruneh faults. We observe signals associated with recent groundwater subsidence, co‐ and postseismic deformation, active salt diaprism, and sediment motion. We derive high‐resolution strain rate estimates on a country‐ and fault‐scale, and discuss the difficulties of mapping diffuse strain rates in areas with abundant non‐tectonic and anthropogenic signals.
Plain Language Summary
Across the entire country of Iran, the ongoing convergence of the Arabian and Eurasian tectonic plates at about two cm every year is deforming the Earth's crust, producing earthquakes in this process of continental collision. Accurate measurements of how the ground is moving today are critical to understanding both the county‐scale deformation, and the local‐scale earthquake hazard, where the crust is deforming quickly and building up strain that is likely to be released in future major earthquakes. We combine multiple series of satellite radar images with GPS velocities to estimate East and vertical ground motion across all of Iran, at a higher level of detail than previous GPS‐only studies have been able to capture. Our velocity fields show a complex mix of ground motion signals, from crustal deformation on a country‐scale, to rapid land subsidence caused by the extraction of groundwater from aquifers. Some of the major faults are clearly building up strain for future earthquakes, but other regions are deforming much more diffusely, making it difficult to ascertain the locations of any future seismic hazard and ground shaking.
Key Points
We generate high‐resolution East and vertical velocity fields for Iran using Sentinel‐1 InSAR and GNSS observations
Regional deformation is diffuse, with interseismic strain localized onto the Doruneh, Main Kopet Dagh, North Tabriz, and Sharoud faults
Iran contains a wealth of time‐varying, short‐wavelength signals associated with groundwater extraction, salt diaprism, and sediment motion
Surface wave dispersion curves from microearthquakes are used to obtain group velocity dispersion maps. The calculation of the local dispersion curves for each grid point from these maps then ...produces the input data to retrieve the 3D shear wave velocity model of the Tehran region. The group velocity maps indicate that the tomographic results agree well with the three main tectonic features and the geological units in the study area. The tomographic maps generally possess high-velocity structures across most of the mountain belts (Central Alborz and east-southeast mountains), whereas the Tehran Basin correlates to a low-velocity structure. Increasing the period in the study area highlights four independent low-velocity zones that reflect faults and fault junction systems. The shear wave velocity profiles indicate that the depth to bedrock exhibits southward variation ranging from ~ 300 m to ~ 1500 m. We also focus our analysis on the existence of faults within the shear wave profiles and discuss the low shear wave velocity anomalies deeper than 2 km result from the main fault structures (e.g., North Tehran, North-South Rey and Parchin). Furthermore, we argue that the dip angle of the North Tehran fault varies along fault strike, whereas the North-South Rey fault possesses a constant dip angle. Moreover, initial model uncertainties and checkerboard resolution tests are used to identify reliable and robust anomaly features in the 3D shear wave velocity model and 2D tomographic maps, respectively. Microearthquake analysis provides an effective approach for studying the upper crustal structure heterogeneity, especially the fault structure, of the Tehran region.
Firn densification profiles are an important parameter for ice‐sheet mass balance and palaeoclimate studies. One conventional method of investigating firn profiles is using seismic refraction ...surveys, but these are difficult to upscale to large‐area measurements. Distributed acoustic sensing (DAS) presents an opportunity for large‐scale seismic measurements of firn with dense spatial sampling and easy deployment, especially when seismic noise is used. We study the feasibility of seismic noise interferometry (SI) on DAS data for characterizing the firn layer at the Rutford Ice Stream, West Antarctica. Dominant seismic energy appears to come from anthropogenic noise and shear‐margin crevasses. The DAS cross‐correlation interferometry yields noisy Rayleigh wave signals. To overcome this, we present two strategies for cross‐correlations: (a) hybrid instruments—correlating a geophone with DAS, and (b) stacking of selected cross‐correlation panels picked in the tau‐p domain. These approaches are validated with results derived from an active survey. Using the retrieved Rayleigh wave dispersion curve, we inverted for a high‐resolution 1D S‐wave velocity profile down to a depth of 100 m. The profile shows a “kink” (velocity gradient inflection) at ∼12 m depth, resulting from a change of compaction mechanism. A triangular DAS array is used to investigate directional variation in velocity, which shows no evident variations thus suggesting a lack of azimuthal anisotropy in the firn. Our results demonstrate the potential of using DAS and SI to image the near‐surface and present a new approach to derive S‐velocity profiles from surface wave inversion in firn studies.
Plain Language Summary
The density distribution (density change with depth) over tens of meters at the top of a glacier is an important feature of ice‐sheet mass balance and palaeoclimate research. It can be estimated using the empirical relationship between density and seismic P‐wave velocity. The P‐wave velocity can be measured using a seismic refraction survey with geophones and active sources. However, refraction seismic surveys are expensive for measurements over large areas. Distributed Acoustic Sensing (DAS) using fiber optic cables to detect seismic waves is an emerging dense spatial sampling seismic acquisition technology. It can be used in conjunction with seismic noise cross‐correlation to make large‐scale measurements easier and cheaper than with conventional geophones. We investigate the feasibility of this approach on Rutford Ice Stream, West Antarctica, and propose two approaches to improve DAS seismic‐noise cross‐correlation results. Surface waves are retrieved by seismic noise cross‐correlation and are used to estimate the S‐wave velocity structure. Our S‐velocity profile resembles an independently measured P‐velocity in‐shape and presents a velocity gradient inflection—related to changes in the snow compaction mechanism. We show that DAS and seismic noise interferometry can be used for future firn measurements, but also more generally in studies of the near‐surface.
Key Points
Distributed acoustic sensing (DAS) is used for the first time to derive the S‐wave velocity structure and anisotropy of the firn layer in Antarctica
DAS seismic interferograms are greatly improved through selective stacking and cross‐correlation with a geophone
Our method is suitable for large‐scale measurements and is feasible in the presence of ice lenses where refraction methods are inadequate
River discharge has to be monitored reliably for effective water management. As river discharge cannot be measured directly, it is usually inferred from the water level. This practice is unreliable ...at places where the relation between water level and flow velocity is ambiguous. In such a case, the continuous measurement of the flow velocity can improve the discharge prediction. The emergence of horizontal acoustic Doppler current profilers (HADCPs) has made it possible to continuously measure the flow velocity. However, the profiling range of HADCPs is limited, so that a single instrument can only partially cover a wide cross section. The total discharge still has to be determined with a model. While the limitations of rating curves are well understood, there is not yet a comprehensive theory to assess the accuracy of discharge predicted from velocity measurements. Such a theory is necessary to discriminate which factors influence the measurements, and to improve instrument deployment as well as discharge prediction. This paper presents a generic method to assess the uncertainty of discharge predicted from range‐limited velocity profiles. The theory shows that a major source of error is the variation of the ratio between the local and cross‐section‐averaged velocity. This variation is large near the banks, where HADCPs are usually deployed and can limit the advantage gained from the velocity measurement. We apply our theory at two gauging stations situated in the Kapuas River, Indonesia. We find that at one of the two stations the index velocity does not outperform a simple rating curve.
Key Points
Accuracy of discharge monitored with range‐limited velocity profilers theoretically explained
Correcting for the variation of the velocity profile over the hydrograph improves accuracy
Index velocity not necessarily superior to stage‐rating when measurements are restricted to the near‐bank region
This study examined changes in movement velocity and surface electromyographic (sEMG) activity of the pectoralis major (PM) and triceps brachii (TB) muscles during the bench press exercise to failure ...against different loads. Fourteen men performed a set to failure with maximum intended velocity, against low (40%‐1 repetition maximum‐RM), moderate (60%‐1RM), and heavy loads (80%‐1RM). Number of repetitions, volume load, mean and peak velocity, and total time increased with decreasing load (40% > 60% > 80%, p < 0.01). sEMG comparisons between different loads were performed by matching time under tension at the initial, middle, and last part of the set. sEMG was higher in the middle and last repetitions, compared with the initial, for all loads in both muscles (p < 0.001). sEMG activity of both muscles was higher in the 60% and 80%‐1RM conditions compared with the 40%1‐RM (p < 0.007). Also, sEMG of both muscles was similar for the 60%‐1RM and 80%‐1RM loads at the initial, middle, and last repetitions, with the exception of the last repetitions for the TB muscle. In contrast, sEMG integrated activity was higher for the 40% 1‐RM and 60% 1‐RM (p < 0.01) compared with the 80% 1‐RM load. Mean velocity loss at exhaustion and drop in sEMG median frequency were greater in the 40% and 60%‐1RM compared with the 80%‐1RM condition (p < 0.05). It was concluded that performing a set to exhaustion with maximum intended velocity using a load of 60% 1‐RM combines the characteristics of the high average sEMG activity of heavier loads, and the high total integrated sEMG observed at lighter loads.
Iron may critically influence the physical properties and thermochemical structures of Earth’s lower mantle. Its effects on thermal conductivity, with possible consequences on heat transfer and ...mantle dynamics, however, remain largely unknown. We measured the lattice thermal conductivity of lower-mantle ferropericlase to 120 GPa using the ultrafast optical pump-probe technique in a diamond anvil cell. The thermal conductivity of ferropericlase with 56% iron significantly drops by a factor of 1.8 across the spin transition around 53 GPa, while that with 8–10% iron increases monotonically with pressure, causing an enhanced iron substitution effect in the low-spin state. Combined with bridgmanite data, modeling of our results provides a self-consistent radial profile of lower-mantle thermal conductivity, which is dominated by pressure, temperature, and iron effects, and shows a twofold increase from top to bottom of the lower mantle. Such increase in thermal conductivity may delay the cooling of the core, while its decrease with iron content may enhance the dynamics of large low shear-wave velocity provinces. Our findings further show that, if hot and strongly enriched in iron, the seismic ultralow velocity zones have exceptionally low conductivity, thus delaying their cooling.
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