Continuous monitoring of blood pressure, an essential measure of health status, typically requires complex, costly, and invasive techniques that can expose patients to risks of complications. ...Continuous, cuffless, and noninvasive blood pressure monitoring methods that correlate measured pulse wave velocity (PWV) to the blood pressure via the Moens–Korteweg (MK) and Hughes Equations, offer promising alternatives. The MK Equation, however, involves two assumptions that do not hold for human arteries, and the Hughes Equation is empirical, without any theoretical basis. The results presented here establish a relation between the blood pressure P and PWV that does not rely on the Hughes Equation nor on the assumptions used in the MK Equation. This relation degenerates to the MK Equation under extremely low blood pressures, and it accurately captures the results of in vitro experiments using artificial blood vessels at comparatively high pressures. For human arteries, which are well characterized by the Fung hyperelastic model, a simple formula between P and PWV is established within the range of human blood pressures. This formula is validated by literature data as well as by experiments on human subjects, with applicability in the determination of blood pressure from PWV in continuous, cuffless, and noninvasive blood pressure monitoring systems.
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%
Elastic properties of antigorite are important for interpretation of seismic mapping of serpentinization in the mantle wedge above subducting slabs. The compressional (VP) and shear (VS) wave ...velocities in pure antigorite aggregates were measured simultaneously up to 8.4 GPa by ultrasonic interferometry. We found that VP increases monotonically with pressure while VS increases with pressure up to about 3 GPa but undergoes a negative pressure dependence above 4 GPa. Compared to other mantle minerals, antigorite exhibits significantly lower P and S wave velocities as well as a higher VP/VS ratio at upper mantle pressures. We modeled velocity reductions manifesting through the formation of antigorite in mantle peridotite and provide compelling evidence that seismic anomalies with low‐velocity and high VP/VS ratios is caused by varying degrees of serpentinization in subduction zones.
Plain Language Summary
Seismic observations have revealed many anomalously low‐velocity regions in mantle wedges above subducting slabs. The inferred reduction in mantle velocity has been attributed to the formation of low‐velocity serpentine in the mantle wedge. We report the new results of high‐pressure ultrasonic measurements on a hot‐pressed polycrystalline sample to determine both compressional and shear wave velocities of pure antigorite up to 8.4 GPa at room temperature. We found that antigorite exhibits significantly lower P and S wave velocities and higher VP/VS ratio than major upper mantle minerals (e.g., garnet, clinopyroxene, orthopyroxene, and olivine) at upper mantle pressures. The experimental results were analyzed to interpret the seismic observations in slow regions and constrain the degree of serpentinization in the mantle wedge above subduction zones. We established precise serpentinization budgets from seismic observations and provided compelling evidence for the interpretation of seismic anomalies of low‐velocity and high‐velocity ratios by serpentinization in different subduction zones. These results will improve our ability to map the distribution of hydrous minerals in slabs through interpretation of low‐velocity anomalies in subduction zones.
Key Points
S wave velocity of antigorite exhibits anomalous pressure dependence above 4 GPa
Antigorite has higher VP/VS ratios than all major upper mantle minerals at high pressures
The degree of serpentinization is constrained by VP as function of pressure up to 8 GPa
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.
The interior structure of Saturn, the depth of its winds, and the mass and age of its rings constrain its formation and evolution. In the final phase of the Cassini mission, the spacecraft dived ...between the planet and its innermost ring, at altitudes of 2600 to 3900 kilometers above the cloud tops. During six of these crossings, a radio link with Earth was monitored to determine the gravitational field of the planet and the mass of its rings. We find that Saturn's gravity deviates from theoretical expectations and requires differential rotation of the atmosphere extending to a depth of at least 9000 kilometers. The total mass of the rings is (1.54 ± 0.49) × 10
kilograms (0.41 ± 0.13 times that of the moon Mimas), indicating that the rings may have formed 10
to 10
years ago.
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
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