Velocity Imaging Research Articles

The Inherited Crustal Structure and Lithospheric Thermal Field Beneath the Sea of Marmara (NW Türkiye): Observations From 3D Gravity Modeling and Seismic Tomography Analysis

AbstractThe North Anatolian Fault (NAF) extends for over 1,000 km across Türkiye and poses significant seismic hazard in the region. The Main Marmara Fault (MMF) segment of the NAF in the Sea of Marmara (NW Türkiye), exhibits along‐strike segmentation in its interseismic strain accumulation. Constraining the lithospheric configuration below the MMF is critical to understand its segmentation and assessing seismic hazard in the area. We present a new 3D lithospheric‐scale density of the Sea of Marmara, that combines gravity modeling and seismic tomography analysis. Using forward and inverse gravity modeling with free‐air gravity data and available constraints of geological units we derived the intra‐crustal density structure. Shear‐wave velocity tomography models provided insights into the temperature and density configuration of the uppermost mantle, and the geometry of the 1330°C isotherm. Our results highlight significant crustal density variations: lower‐density crust in the Sakarya Zone and Strandja Massif, and denser crust below the Istanbul Zone, which overlies a relatively hotter lithospheric mantle. This lithospheric configuration reflects both ongoing tectonic processes and inheritance from past geological events, including the drifting of the Istanbul Zone crustal block and the signature of past subduction events. The extent of the Istanbul Zone denser crust spatially correlates with the locked segment of the MMF. The bimaterial nature of the fault segment likely influences its interseismic and coseismic behavior. The denser, stiffer Istanbul Zone crust would promote interseismically locked conditions in contrast to the adjacent, more compliant crustal block and could result in asymmetric rupture with a preferred directivity.

A high-resolution photoelectron spectroscopic and computational study of TaX− (X = C, N, O)

We report on the high-resolution photoelectron spectroscopy of diatomic molecules TaX− (X = C, N, O) anions using a cryogenic ion trap combined with the slow electron velocity imaging (cryo-SEVI) method. We determined the electron affinities of TaC, TaN, and TaO to be 2.098(2), 1.576(2), and 1.069(2) eV, respectively. In addition, the electron affinities of TaX molecules were calculated using the CCSD(T) method with the complete basis sets. To interpret the complicated photoelectron spectra, we predicted the excited states of TaX molecules using the MRCI + Q method, accounting for the spin–orbit coupling effects. Several new excited states of these molecules were observed.

Global left ventricular relaxation index in predicting cardiac cellular rejection in paediatric heart transplant patients.

Endomyocardial biopsy remains the gold standard for cardiac cellular rejection surveillance after heart transplantation. We studied a novel non-invasive index of left ventricular relaxation to detect cardiac cellular rejection in paediatric heart transplant patients. This is a single-centre retrospective study of paediatric heart transplant patients who underwent endomyocardial biopsy from June 2014 to September 2021. Left ventricular relaxation index was calculated as the sum of diastolic tissue Doppler imaging velocities (E) of the left ventricular lateral, septal, and posterior walls divided by the percentage of the left ventricular posterior wall thinning by M-mode. Statistical analysis included t-tests and Mann-Whitney tests to compare means and medians between treatment and non-treatment groups. We used the cut-off with the maximum Youden index to compare the sensitivity and specificity of left ventricular relaxation index to detect rejection. The study included 65 patients who underwent 246 cardiac catheterizations and endomyocardial biopsies. Out of 246, 192 procedures were included and 54 were excluded due to recent transplants or lack of echocardiographic data. A total of 114 demonstrated Grade 0R, 68 Grade 1R, 8 Grade 2R, and 2 Grade 3R allograft rejection. The difference in mean left ventricular relaxation index between treatment versus non-treatment groups (2R, 3R vs. 0R, 1R) was not statistically significant (p = 0.917). A left ventricular relaxation index cut-off of 0.73 had the highest Youden index with good sensitivity (100%) and poor specificity (23%) for detecting rejections with grades 2R and 3R. Left ventricular relaxation index, a novel index of left ventricular relaxation, was not a sensitive or specific predictor of cardiac cellular rejection in paediatric heart transplants.

Research on Occurrence Law and the Prevention of Rockbursts in Main Roadways Affected by Mining Activities: Two Case Studies from Gaojiapu and Cuimu Coal Mines, Shaanxi, China

Rockburst, one of the leading types of disaster in mining and rock engineering causing serious injuries and the loss of property, frequently occurs, involving various features and complex evolutionary mechanisms. Compared to rockbursts occurring at mining faces, those occurring in main roadways cause more serious problems for mine production. This paper first analyzes the characteristics of rockbursts in main roadways using two case studies involving the Gaojiapu and Cuimu coal mines. The causes of rockbursts in main roadways were studied using microseismic monitoring, energy density cloud maps, and seismic velocity tomography. During the mining of the 22306 working face in the Cuimu coal mine, targeted measures, such as deep-hole blasting of the roof strata and deep-hole blasting of the coal seam, were implemented to prevent rockbursts in the main roadways. The effectiveness of these measures was verified through long-term analysis of tremor activities. The study found that the influence of mining at two working faces on both sides of main roadways was significantly greater than that from a single-sided working face. The intensity of the tremor activities occurring near the main roadways was correlated with the distance from the working face to the main roadways. The closer the working face was to the main roadways, the stronger the tremor activities were near the main roadways. According to the distribution range of the tremors, the influence area of working face mining exceeded 800 m, with tremors distributed linearly along the main roadways. Even five months after the completion of working face mining, there were still a large number of tremors near the main roadways, which gradually disappeared after another five months. Mining activities were the main reason for the occurrence of main roadway rockbursts and the stress concentration within the main roadways themselves was another reason for the occurrence of rockbursts. The influence of working face mining could be reduced by deep-hole blasting of roof strata and the stress concentration within main roadways themselves could be reduced by large-diameter drilling. Those joint preventive measures effectively prevented the occurrence of rockbursts in main roadways. This study is of important theoretical and practical significance for further studies of rockburst mechanisms and prevention in regard to main roadways in coal mines, and the findings are significant in terms of the enhancement of safety in coal mines.

Geophysical visualization of water content distribution in bentonite by joint seismic and radar tomography

SUMMARY Bentonite is often considered as buffer material for deep geological radioactive waste repositories. To support decision making and safety assessment of radioactive waste repositories, international agencies and research institutions proposed the implementation of monitoring programmes. While the overall concepts of such monitoring programmes have been largely developed, the selection of key observations parameters, such as temperature, pressure and water content, and the technical implementation are still under development. The direct measurement of such parameters requires the placement of sensors inside a repository, which can significantly affect its safety functions and only provides information at the typically sparse sensor locations. Geophysical tomography can help gaining valuable insights into the state of the repository non-invasively by providing images of the distribution of geophysical parameters from measurements that are purely taken from the outside. However, the extracted geophysical parameters are often difficult to interpret and the geophysical tomography problem is non-unique, meaning that there exist multiple models that explain the data equally well. Here, we demonstrate that this non-uniqueness can be significantly reduced by simultaneously employing multiple geophysical methods in a joint tomography scheme. We simultaneously invert seismic and ground penetrating radar (GPR) traveltimes and amplitudes by imposing structural similarity constraints on the tomographic velocity and attenuation images. The resulting, estimated geophysical parameter maps show a strongly improved correlation when compared to results obtained from individual inversions, which in turn facilitates the establishment of constitutive relationships between the geophysical parameters (seismic and GPR velocity and attenuation) with the water content, as key parameter for the evaluation of the state of a radioactive waste repository. Using data from the full-scale emplacement (FE) experiment, we employ a supervised machine-learning model that enables the translation of the tomographic velocity and attenuation images obtained in bentonite to an image of the distribution of the water content inside the repository, where the machine learning model is trained using direct point measurements of the water content at sparse locations inside the tomographic plane. Due to the lack of direct water content sensors in the FE experiment, we use neutron log data (which are directly linked to water content) to train the machine learning model. Ultimately, this enables us to extrapolate the sparse neutron log data to a spatially cohesive distribution inside the repository corresponding to a visualization of the spatial distribution of water content.

Experimental study on identifying anomaly azimuth based on acoustic vector array of borehole acoustic reflection imaging

Accurate anomaly azimuth identification is a major challenge in borehole acoustic reflection imaging. We develop an azimuth estimation method using an acoustic vector array to address this issue. This method is rigorously tested through a physical simulation experiment in a water-filled tank using a monopole acoustic source and an acoustic receiver station composed of eight azimuthal elements. Our method involves the synthesis of multiazimuth acoustic pressure waveforms recorded by the receiver into multicomponent particle velocity waveforms. These waveforms are paired and subjected to coordinate conversion, yielding multiple groups of orthogonal component particle velocity waveforms. Each group undergoes polarization analysis to obtain the direction of particle polarization on the horizontal plane and isolate the principal component particle velocity waveform. Using the particle polarization direction, the amplitude of the multiazimuth acoustic pressure waveform, and the type of echo mode, we accurately determine the azimuth of the anomaly, facilitating the creation of a spatial distribution image of the anomaly. Further validation of this method is conducted through a large-scale physical simulation experiment in a deepwater lake using a borehole acoustic reflection imaging instrument. The obtained experimental data are used to validate the effectiveness of this method. Finally, considering an actual logging environment, the feasibility of this method in a borehole environment is verified using numerical simulations and field data of acoustic detection of nearby wells. The present findings demonstrate that this novel method considerably enhances the accuracy and stability of the measurement of anomaly azimuth based on the particle polarization direction. In addition, this method effectively harnesses acoustic pressure and particle velocity in borehole acoustic reflection imaging, exhibiting superior noise robustness, mitigating noise, and improving the signal-to-noise ratio of the echoes.

CME Velocity Field Calculation Model Based on an Unsupervised Transformer Optical Flow Network

The optical flow algorithm (OF) is one the main methods for calculating image velocity field and has many applications in space weather. Most OF calculations are applied to the motion of labeled rigid objects and are not suitable for velocity detection of high-energy particles, such as in a coronal mass ejection (CME). Fluctuations in exposure time and the influence of space weather will lead to inconsistent brightness of the same feature point at different times. To address this problem, we propose an unsupervised multiscale optical flow network based on Vision Transformer, named UTFlowNet. The network comprises a multiscale feature extraction module and a coarse-to-fine global optical flow calculation module. The movement of high-energy particles emitted during a CME eruption follows certain physical rules. Therefore, we apply fluid motion–based loss functions to analyze the motion of high-energy particles more effectively, addressing the problem of CME motion field extraction. Our method can be applied to the real-time automatic extraction of a CME’s velocity field and performs well with inconsistent brightness, large-scale motion, and strong CME noise. Additionally, we can estimate subpixel level fine-grained velocity. Our model may be affected by overfitting during cross–data set inference, so we encourage performing a small amount of transfer learning on new data sets to mitigate this issue. In order to verify the accuracy of our method, we conducted experiments and verification on the Solar and Heliospheric Observatory LASCO C2 data and the High Altitude Observatory MLSO data. We constructed a large-scale displacement simulation data set based on LASCO C2 data and tested on it, achieving the best results.

Radon-domain acoustic and elastodynamic interferometric redatuming of VSP data

SUMMARY The virtual source method (VSM) is a useful tool for imaging and monitoring below complex and time-varying overburden. When it is applied to VSP geometries, the redatumed virtual source data often suffer from artifacts and aliasing due to the violation of theoretical acquisition conditions and partial focusing of virtual multiples, which further degrade seismic imaging quality. While the conventional Radon-domain VSM (R-VSM) mitigates these issues to some extent, it is still possible to improve upon the imaging. This study develops a simple and effective high-resolution Radon-domain VSM (HR-VSM) to effectively address these issues, offering superior noise and artifact suppression compared to traditional VSM and R-VSM. HR-VSM shows a strong performance across a wide range of VSP configurations and data types, especially in applications to multicomponent and passive seismic data, demonstrating its versatility and effectiveness in seismic exploration and showing potential for use in earthquake seismology. To extend subsurface illumination, we combined correlation-type and convolution-type HR-VSM for automatically redatuming virtual surface seismic profile shot gathers with a complete receiver array covering all surface source locations, without the additional pre-processing steps typically required by VSM. It was also tested on reverse VSP synthetic active data and passive seismic data, proving effective in constructing virtual shot gathers and showing potential for extending its use to earthquake data and ambient-noise seismology. Moreover, HR-VSM can perform elastodynamic interferometric redatuming, enabling the redatuming of pure P-P and pure P-SV waves from multicomponent VSP data. We applied HR-VSM to redatum virtual single well profile data containing fault-related P-P and P-SV reflections from VSP data, which were further used for fault imaging. Finally, HR-VSM was used to generate virtual crosswell data with receivers in both boreholes, eliminating the need for downhole sources. The obtained virtual crosswell containing direct waves, as well as P-P and P-SV reflections, enable constructing a velocity model and imaging the structure between wells.

Scalable Copper Sulfide Formulations for Super-Resolution Optoacoustic Brain Imaging in the Second Near-Infrared Window.

Optoacoustic imaging offers label-free multi-parametric characterization of cerebrovascular morphology and hemodynamics at depths and spatiotemporal resolution unattainable with optical microscopy. Effective imaging depth can greatly be enhanced by employing photons in the second near-infrared (NIR-II) window. However, diminished absorption by hemoglobin along with a lack of suitable contrast agents hinder an efficient application of the technique in this spectral range. Herein, copper sulfide (CuS) micro- and nano-formulations for multi-scale optoacoustic imaging in the NIR-II window are introduced. Dynamic contrast enhancement induced by intravenously administered CuS nanoparticles facilitated visualization of blood perfusion in murine cerebrovascular networks. The individual calcium carbonate microparticles carrying CuS are further shown to generate sufficient responses to enable super-resolution microvascular imaging and blood flow velocity mapping with localization optoacoustic tomography.

Crustal Structure of Southern California from Velocity and Attenuation Tomography

Recent studies of Southern California have employed velocity and attenuation tomography to elucidate two aspects of crustal structure. Low-frequency velocity tomography reveals large-scale heterogeneity that can be approximated by a discrete set (𝐾 ≤ 10) of tectonic regions, each characterized by an isostatically balanced lithospheric column reflecting the composition and tectonic history of the region. The boundaries between tectonic regions are typically localized structures expressed at the surface by major faults, topographic fronts, and geochemical transitions. The efficacy with which tomographic regionalization (TR) represents the subsurface geography of major tectonic units in Southern California indicates that the TR idealization works surprisingly well in this part of the Pacific‐North America plate boundary. High‐frequency attenuation tomography in Southern California supports the hypothesis that the decay of P and S waves propagating through the upper and middle crust is dominated by elastic scattering from small-scale heterogeneities of high fractal dimension, rather than by anelastic dissipation. The amplitude of the scattering varies systematically among the tectonic regions and correlates with the degree of recent faulting and deformation within a region. These results motivate speculation that small-scale crustal heterogeneities responsible for high-frequency attenuation are generated within the seismogenic zone through a dynamic interplay between distributed deformation and localized fracturing.

Investigation of droplet splashing behavior during oblique jet impact onto a wall

For the issue of jet impingement on the wall in industrial cooling processes, an experimental setup based on high-speed photography for oblique jet impingement onto the wall was constructed. The experimental focus was on the study of liquid droplet splashing behavior after oblique jet impingement on the wall, discussing the liquid droplet splashing behavior under three jet impingement modes: Rayleigh regime, first wind-induced regime, and secondary wind-induced regime. By employing methods such as trajectory imaging and particle image velocity for liquid droplet parameter image measurement, obtaining the particle size, velocity, and distribution of splashed droplets after oblique jet impact on walls under different working conditions. The impact of jet impingement velocity and angle on droplet splashing parameters was analyzed. The results showed that when the impingement point is before the breakup length, with increasing flow velocity, the surface wave of the liquid column, and the spreading liquid film became more pronounced, but the loss of liquid-phase components due to splashing was relatively small. When the impingement point is after the breakup length, the secondary breakup resulting in a “crown”-shaped liquid film after droplet impingement leads to a significant loss of liquid-phase components through splashing. As the inlet velocity of the jet increases, there is a decreasing trend in droplet size and an increasing trend in droplet velocity. With an increase in jet angle, there is a decreasing trend in droplet size and velocity. Based on the concentration, size, and velocity distribution characteristics of splashing droplets, the area after oblique jet impingement on the wall can be divided into the impingement zone, low-concentration low-velocity zone, high-concentration high-velocity zone, and lateral splashing zone. This has significant implications for understanding the splashing mechanism after oblique jet impingement on the wall and optimizing operating conditions.

High-resolution anionic velocity map imaging apparatus for dissociative electron attachment dynamics study.

Dissociative electron attachment (DEA) of a molecular target XY, e- + XY → XY- → X + Y-, is an important process in plasma, atmosphere, interstellar space, and ionizing radiation. DEA dynamics, i.e., the formation and fragmentation of an electron-molecule resonant complex, can be unveiled by measuring the product Y- with the velocity map imaging (VMI) technique. However, it is still challenging to achieve a high-resolution VMI measurement. Recently, we developed a high-resolution DEA apparatus that combined the VMI technique with a trochoidal electron monochromator. The energy spread (around 500meV) of thermally emitted incident electrons can be reduced remarkably, but the monochromatized electrons become diffuse again in energy when being pulsed with an electric pulse applied on the grid electrode because the electron beam must be pulsed in the VMI measurement. Now this long-standing technical contradiction is settled by introducing a parallel resistance-capacitor circuit to the electrode of an electron gun. A delay-line detector is used for the VMI measurement, which allows the three-dimensional velocity or momentum images of multiple anionic yields to be recorded efficiently. Our high-resolution VMI apparatus works at a pulse frequency of 5kHz and an energy spread of about 120-150meV, and its credible performances are exhibited by the measurements of the DEA processes of CO(a3Π) and NO2.

A Radar-Based Concept for Simultaneous High-Resolution Imaging and Pixel-Wise Velocity Analysis for Tracking Human Motion

A Radar-Based Concept for Simultaneous High-Resolution Imaging and Pixel-Wise Velocity Analysis for Tracking Human Motion

Extraction of ADCIGs in viscoelastic media based on fractional viscoelastic equations

Angle domain common imaging gathers (ADCIGs) serve as not only an ideal approach for tomographic velocity modeling but also as a crucial means of mitigating low-frequency noise. Thus, they play a significant role in seismic data processing. Recently, the Poynting vector method, due to its lower computational requirements and higher resolution, has become a commonly used approach for obtaining ADCIGs. However, due to the viscoelastic properties of underground media, attenuation effects (phase dispersion and amplitude attenuation) have become a factor, which is important in seismic data processing. However, the primary applications of ADCIGs are currently confined to acoustic and elastic media. To assess the influence of attenuation and elastic effects on ADCIGs, we introduce an extraction method for ADCIGs based on fractional viscoelastic equations. This method enhances ADCIGs accuracy by simultaneously considering both the attenuation and elastic properties of underground media. Meanwhile, the S-wave quasi tensor is used to reduce the impact of P-wave energy on S-wave stress, thus further increasing the accuracy of PS-ADCIGs. In conclusion, our analysis examines the impact of the quality factor Q on ADCIGs and offers theoretical guidance for parameter inversion.

A comprehensive diagnostic approach to differentiate intrauterine arteriovenous malformation in cases of enhanced myometrial vascularity.

The differentiation between conditions such as uterine arteriovenous malformation, pseudoaneurysm, gestational trophoblastic disease, and retained trophoblastic tissue can be challenging. Ultrasound imaging and Doppler interrogation are the primary diagnostic tools to assess cases of enhanced myometrial vascularity and differentiate intrauterine vascular anomalies. However, some cases remain of difficult differentiation. This study aims to analyze suspected cases and describe their diagnostic management and outcomes. We reviewed post-abortion cases that underwent pelvic transvaginal U/S imaging and Doppler examinations due to suspected uterine vascular anomalies. CT scans were performed in cases in which ultrasound did not reach a diagnosis. Simple follow-up, medical or surgical therapy, or embolization of uterine arteries were performed according to the final diagnosis. From 2015 to 2022, we retrieved from electronic ultrasound records 22 cases of suspected vascular malformations. In eight cases, first-line U/S at admission excluded the suspected anomaly.In Five ofthe remaining 14 patients, uterine vascular anomalies were excluded upon a second-level U/S based on angio-Doppler imaging and Doppler peak velocity interrogation. Nine cases underwent CT scan, and a digital angiography and embolization were performed in eight of these cases, of whom only two had a documented uterine arteriovenous malformation. Our triage proved that only two out of 22 suspected cases had a uterine arteriovenous malformation. This diagnosis is frequently misused in clinical practice. Our data confirm that enhanced myometrial vascularity should be used to encompass the spectrum of possible differential diagnosis. A precise step-by-step diagnostic method is of paramount importance to prevent unnecessary interventions.

Is the mantle transition zone uniform beneath Precambrian shields?

In the present study, we examine the mantle transition zone (MTZ) structure below the prominent Precambrian shields on the Earth to understand its thermal and compositional properties and depth distribution of MTZ discontinuities. For this study, we used data from Canadian, Brazilian, Baltic, African and Australian Shields. We migrate the receiver functions to the depth domain using 3D tomographic models to examine the topography of MTZ discontinuities that define the upper and lower boundaries of the MTZ. The depth migration results were obtained using two different 3D tomographic velocity models, LLNL_G3D_JPS and GyPSuM. The analysis shows that both models yield similar results. The findings indicate a thinner than usual MTZ beneath all the Precambrian shields with an average thickness of ∼238 ± 8 km. Notably, the present study reveals the upper boundary of the MTZ (410 km discontinuity) displays distinctive topography; in contrast, the lower boundary of the MTZ (660 km discontinuity) is situated at shallower depths. Therefore, the main factor causing the variation in MTZ thickness is the shallowing of the 660 km discontinuity, indicating that the post-spinel transition occurred at higher temperatures with a negative Clapeyron slope, supporting the theory of whole-mantle convection. This suggests that mantle plumes have some appreciable impact on the MTZ beneath Precambrian shields, which are limited to the base of the MTZ. Alternatively, the global mantle warming explanation could be invoked, as it best explains the similar characteristics of the 660 km discontinuity beneath the Precambrian shields. However, this phenomenon needs to be tested through numerical modelling.

Exploring ice melting dynamics in beverageware

The ice-melting process inside water-filled beverageware is studied experimentally, theoretically, and numerically. An ice body is immersed in warm fresh water in different-shaped glass cups. The ice body eventually melts due to heat transfer from the warmer fluid to the ice. As the ice melts and cools the surrounding fluid, it promotes complex time-dependent laminar flows characterized by a vertical downward jet beneath the ice body and rotating convective cells in the fluid domain. Experimental results obtained through dye visualization, particle image velocity, and local temperature measurements show that the size and number of the rotating cells, jet velocity, and melting time of the ice depend significantly on the shape of the beverageware. A one-dimensional analytical solution reproduces qualitatively the hydrodynamical and thermal boundary layers close to the ice body. Further, a two-dimensional numerical model correctly captures the main features of the experimental observations.

How Fluid Pseudoplasticity and Elasticity Affect Propeller Flows in Biogas Fermenters

AbstractMixing in biogas fermenters is complex due to the non‐Newtonian rheology of biogenic substrates, which exhibit both pseudoplasticity and elasticity. It is yet unclear how these non‐Newtonian properties affect propeller flows and the mixing behavior in fermenters. Therefore, propeller flows in Newtonian as well as shear‐thinning inelastic and elastic fluids are compared numerically and validated against particle image velocity (PIV) data. Elastic normal stresses lead to an increase of pumping rates in the laminar regime and a suppression of the formation of a propeller jet in the transitional regime. Thus, flow rates are severely overestimated by the inelastic, shear‐thinning model in this regime. The results indicate that elasticity is critical for an accurate modeling of flows of biogenic substrates.

Estimated Pulse-Wave Velocity and Magnetic Resonance Imaging Markers of Cerebral Small-Vessel Disease in the NOMAS.

Pulse-wave velocity is a measure of arterial stiffness and a risk factor for cardiovascular disease. Recently, an estimated pulse-wave velocity (ePWV) was introduced that was predictive of increased risk of cardiovascular disease. Our objective was to determine whether ePWV was associated with cerebral small-vessel disease on magnetic resonance imaging. We included 1257 participants from the NOMAS (Northern Manhattan Study). The ePWV values were calculated using a nonlinear function of age and mean arterial blood pressure. The association between ePWV and white matter hyperintensity volume was assessed. Modification by race and ethnicity was evaluated. Associations between ePWV and other cerebral small-vessel disease markers, covert brain infarcts, cerebral microbleeds, and enlarged perivascular spaces, were explored as secondary outcomes. Mean±SD age of the cohort was 64±8 years; 61% were women; 18% self-identified as non-Hispanic Black, 67% as Hispanic, and 15% as non-Hispanic White individuals. Mean±SD ePWV was 11±2 m/s in the total NOMAS population and was similar across race and ethnic groups. The ePWV was significantly associated with white matter hyperintensity volume (β=0.23 [95% CI, 0.20-0.26]) after adjustment. Race and ethnicity modified the association between ePWV and white matter hyperintensity volume, with stronger associations in Hispanic and non-Hispanic Black individuals. Significant associations were found between ePWV and covert brain infarcts, cerebral microbleeds, and perivascular spaces after adjustment. The ePWV function may provide a vascular mechanism for deleterious cerebrovascular outcomes in individuals with cerebral small-vessel disease and is particularly apparent in the racial and ethnic minorities represented in the NOMAS cohort.

Spatial Distribution of Tremor Episodes From Long‐Term Monitoring in the Northern Cascadia Subduction Zone

AbstractLarge bursts of non‐volcanic tremor (“major” tremor episodes) correlated with geodetic deformation recur regularly in the Cascadia subduction zone and are often called episodic tremor and slip (ETS). Minor episodes of tremor between ETS are ubiquitous but have been understudied. This paper assesses time‐invariant characteristics of tremor episodes of all sizes within northern Cascadia. We derive a catalog of tremor episodes ranging in size from 10 to >13,000 tremor events using the results of 17 years of tremor monitoring. Minor episodes represent ∼96% of all 896 tremor episodes and their occurrence varies on 10‐km scales. Using estimates for the depth of the forearc Moho and subducting slab, we observe an association between the location of the forearc mantle corner (FMC) and tremor occurrence that leads to along‐dip modality. Bimodality, present in southern Washington and Vancouver Island, represents the segmentation of major and minor episodes up‐dip and down‐dip of the FMC, respectively. Unimodality, present in Puget Sound, results when the FMC is located near the down‐dip edge of the ETS zone and no segmentation occurs. We also use our extensive tremor episode catalog alongside three‐dimensional regional tomographic velocity models to reassess the relationship between tremor activity and low Vp/Vs signatures in the forearc. We do not find a correlation between tremor episode recurrence intervals and Vp/Vs, contrary to some previous work, suggesting that controls on silica precipitation in the forearc crust are not dominant controls of tremor episode recurrence, or that the association is not widely observable.