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The authors prove the existence and the linear stability of small amplitude time quasi-periodic standing wave solutions (i.e. periodic and even in the space variable x) of a 2-dimensional ocean with infinite depth under the action of gravity and surface tension. Such an existence result is obtained for all the values of the surface tension belonging to a Borel set of asymptotically full Lebesgue measure.

The fluid-saturated porous layered (FSPL) media widely exist in the Earth’s subsurface and their overall mechanical properties, microscopic pore structure and wave propagation characteristics are highly relevant to the in-situ stress. However, the effect of in-situ stress on wave propagation in FSPL media cannot be well explained with the existing theories. To fill this gap, we propose the dynamic equations for FSPL media under the effect of in-situ stress based on the theories of poroacoustoelasticity and anisotropic elasticity. Biot loss mechanism is considered to account for the stress-dependent wave dispersion and attenuation induced by global wave-induced fluid flow. Thomsen’s elastic anisotropy parameters are used to represent the anisotropy of the skeleton. A plane-wave analysis is implemented on dynamic equations yields the analytic solutions for fast and slow P waves and two S waves. Modelling results show that the elastic anisotropy parameters significantly determine the stress dependence of wave velocities. Vertical tortuosity and permeability have remarkable effects on fast and slow P-wave velocity curves and the corresponding attenuation peaks but have little effect on S-wave velocity. The difference in velocities of two S waves occurs when the FSPL medium is subjected to horizontal uniaxial stress, and the S wave along the stress direction has a larger velocity, which implies that the additional anisotropy other than that induced by the beddings appears due to horizontal stress. Besides, the predicted velocity results have the reasonable agreement with laboratory measurements. Our equations and results are relevant to a better understanding of wave propagation in deep strata, which provide some new theoretical insights in the rock physics, hydrocarbon exploration and stress detection in deep-strata shale reservoirs.

The effect of stress on wave propagation in fluid-saturated porous thermoelastic media is poorly understood. To fill this gap, we propose the dynamical equations for stressed fluid-saturated porous thermoelastic media based on the poroacoustoelasticity model and porothermoelasticity model to describe the effect of stress on the wave dispersion and attenuation. A plane-wave analysis for dynamical equations formulates stress-dependent velocities of five wave propagation modes, including three longitudinal (P) waves, namely fast P wave, slow P wave and thermal (T) wave, and two shear (S) waves, namely fast S wave and slow S wave. Additional slow P wave and T wave arise due to the Biot and thermal loss mechanisms in porothermoelastic media. The stress-induced rock anisotropy accounts for the S wave splitting phenomenon. Modelling results show that energy dissipations of fast P wave and T wave are induced by the coupling between Biot and thermal loss mechanisms, while the fast and slow S waves, slow P wave are only affected by Biot loss mechanism. The rock permeability and fluid viscosity are mainly related to Biot mechanism, while the thermal conductivity and thermal expansion coefficient for solid phase are related to Biot and thermal mechanisms. In addition, the triaxial stress and confining stress have remarkable effects on the wave velocities as well as attenuation peaks. The predicted wave velocities in water-saturated sandstone and granite behave a reasonable agreement with the laboratory measurements. Our results help to provide better understanding of wave propagation in high-stress high-temperature fields.Article HighlightsWe propose the dynamical equations for fluid-saturated porous thermoelastic media with the effect of stress.Our model predicts five wave propagation modes, namely fast P wave, slow P wave, thermal wave, fast S wave and slow S wave.Biot and Thermal loss mechanisms are coupled to describe the stress-dependent dispersions and attenuations for these five wave modes.

The Eastern United States (EUS) has a complex geological history and hosts several seismic active regions. We investigate the subsurface structure beneath the broader EUS. To produce reliable images of the subsurface, we simultaneously invert smoothed P‐wave receiver functions, Rayleigh‐wave phase and group velocity measurements, and Bouguer gravity observations for the 3D shear‐wave speed. Using surface‐wave observations (3–250 s) and spatially smoothed receiver functions, our velocity models are robust, reliable, and rich in detail. The shear‐wave velocity models fit all three types of observations well. The resulting velocity model for the eastern U.S. shows thinner crust beneath New England, the east coast, and the Mississippi Embayment (ME). A relatively thicker crust was found beneath the stable North America craton. A relatively slower upper mantle was imaged beneath New England, the east coast, and western ME. A comparison of crust thickness derived from our model against four recent published models shows first‐order consistency. A relatively small upper mantle low‐speed region correlates with a published P‐wave analysis that has associated the anomaly with a 75 Ma kimberlite volcanic site in Kentucky. We also explored the relationship between the subsurface structure and seismicity in the eastern U.S. We found that earthquakes often locate near regions with seismic velocity variations, but not universally. Not all regions of significant subsurface wave speed changes are loci of seismicity. A weak correlation between upper mantle shear velocity and earthquake focal mechanism has been observed. Plain Language Summary The Eastern United States (EUS) experienced a complex series of geological activities. Earthquakes in the EUS have been recorded at several localized regions. A detailed subsurface structure can help us recover the geological history and studying earthquakes. We use multiple types of geophysical observations to reliably image the subsurface. Our images of the subsurface confirmed many findings from previous studies. The crust is thinner beneath New England, the east coast, and the southcentral United States. The interior of North America has a thicker crust. The upper mantle seismic speed is shower beneath New England, the east coast, and the western portion of the southcentral United States. A smaller region of slower upper mantle speed in Kentucky agrees with a published study, which linked the slower speed with a 75 Ma volcanic site. We compared images of subsurface against earthquake locations. Earthquakes often locate near regions with lateral subsurface structure changes. Lateral subsurface structure changes do not always collocate with earthquakes. The type (faulting) of earthquakes weakly correlates with the upper mantle seismic speed. Key Points Inverting smoothed receiver functions, surface‐wave dispersion, and gravity for a 3D shear‐wave velocity model for the eastern US Our velocity model is broadly consistent with published results for the region Earthquakes often but not universally locate near areas with seismic speed variation, but not all velocity changes are loci of seismicity

BackgroundTo investigate the changes of P wave indices in atrial fibrillation (AF) patients after catheter ablation and the association between P wave indices and AF recurrence.MethodsPubMed, Embase, and Cochrane Database were searched through September 15th 2021 for studies on the association between P wave indices and AF with catheter ablation. Heterogeneity was estimated using the I2 statistic, the random effects model was used to calculate the pooled results, and summary receiver operating characteristic curve (SROC) was used to evaluate the predictive value.ResultsAmong included fourteen studies with 1674 AF patients, we found significantly decreased P wave dispersion (Pdis) (mean difference [MD]: − 6.5 ms, 95% confidence interval [95% CI]: − 11.81 to − 1.18, P = 0.02) after cryoballoon ablation (CBA) or radiofrequency ablation (RFA), and maximum P wave (Pmax) (MD: − 8.57 ms, 95% CI: − 17.03 to − 0.10, P = 0.05) after RFA only, but increased minimum P wave (Pmin) (MD: 3.43 ms, 95% CI: 1.07 to 5.79, P < 0.01) after CBA only. Pdis measured before ablation was remarkably higher (MD: 5.79 ms, 95% CI: 2.23 to 9.36, P < 0.01) in patients with recurrence than without; meanwhile, Pmax was higher measured both before and after ablation (MD: 6.49 ms, 95% CI: 2.30 to 10.69, P < 0.01 and MD: 11.2 ms, 95% CI: 2.88 to 19.52, P < 0.01). Furthermore, SROC analysis showed acceptable predictive efficiencies of Pdis (AUC = 0.776) and Pmax (AUC = 0.759) for AF recurrence.ConclusionPdis was significantly decreased after AF catheter ablation. Higher Pdis and Pmax may have predictive values for AF recurrence.

The geotechnical industry has widely adopted the refraction microtremor shear-wave velocity measurement technique, which is accepted by building authorities for evaluation of seismic site class around the world. Clark County and the City of Henderson, Nevada, populated their Earthquake Parcel Map with over 10,000 site measurements for building code enforcement, made over a 3-year period. 2D refraction microtremor analysis now allows engineers to image lateral shear-wave velocity variations and do passive subsurface imaging. Along with experience at a basic level, the ability to identify the “no energy area” and the “minimum-velocity envelope” on the slowness-frequency (p-f) image helps practitioners to assess the quality of their ReMi data and analysis. Guides for grading (p-f) image quality, and for estimating depth sensitivity, velocity-depth tradeoffs, and depth and velocity resolution also assist practitioners in deciding whether their refraction microtremor data will meet their investigation objectives. Commercial refraction microtremor surveys use linear arrays, and a new criterion of 2.2% minimum microtremor energy in the array direction allows users to assess the likelihood of correct results. Unfortunately, any useful and popular measurement technique can be abused. Practitioners must follow correct data collection, analysis, interpretation, and measurement procedures, or the results cannot be labeled “refraction microtremor” or “ReMi” results. We present some of the common mistakes and provide solutions with the objective of establishing a “best practices” template for getting consistent, reliable models from refraction microtremor measurements.

The fault generated transient traveling waves are wide band signals which cover the whole frequency range. When the frequency characteristic of line parameters is considered, different frequency components of traveling wave will have different attenuation values and wave velocities, which is defined as the dispersion effect of traveling wave. Because of the dispersion effect, the rise or fall time of the wavefront becomes longer, which decreases the singularity of traveling wave and makes it difficult to determine the arrival time and velocity of traveling wave. Furthermore, the dispersion effect seriously affects the accuracy and reliability of fault location. In this paper, a novel double-ended fault location method has been proposed with compensating the dispersion effect of traveling wave in wavelet domain. From the propagation theory of traveling wave, a correction function is established within a certain limit band to compensate the dispersion effect of traveling wave. Based on the determined arrival time and velocity of traveling wave, the fault distance can be calculated precisely by utilizing the proposed method. The simulation experiments have been carried out in ATP/EMTP software, and simulation results demonstrate that, compared with the traditional traveling-wave fault location methods, the proposed method can significantly improve the accuracy of fault location. Moreover, the proposed method is insensitive to different fault conditions, and it is adaptive to both transposed and untransposed transmission lines well.

Objectives The aim of this study was to evaluate the diagnostic performance of shear wave elastography (SWE), shear wave dispersion (SWD), and attenuation imaging (ATI) in assessment of hepatic parenchyma in patients with liver tumors before resection. Methods Patients with liver tumors were prospectively enrolled in this study. All participants underwent SWE, SWD, and ATI examinations. Fibrosis stage, necroinflammatory activity and hepatic steatosis grade were determined histopathologically. We evaluated the stability of ATI, SWE and SWD examinations. Multivariable linear regression analyses were conducted to determine the determinant factors for SWE, SWD, attenuation coefficient (AC) values. A receiver operating characteristic (ROC) curve analysis was used to evaluate diagnostic performance of multiparametric US (ultrasond). Results A total of 280 participants were enrolled in this study. TG (triglyceride) and steatosis for AC value were significant determinant factors. PLT (platelet), PT (prothrombin time), GGT (glutamyl transpeptidase), and fibrosis stage for SWE value were significant determinant factors. PLT, fibrosis stage and inflammation activity for SWD value were significant determinant factors. AC value was correlated with hepatic steatosis. Both SWE and SWD values were correlated with fibrosis stage, inflammation activity, respectively. The area under the ROC (AUROC) curve of ATI for predicting hepatic steatosis grade were 0.910(≥ S1), 0.927(≥ S2), 0.962(= S3), respectively. The AUROC curve of SWE for predicting fibrosis stage were 0.923(≥ S1), 0.934(≥ S2), 0.930(≥ S3), 0.895(= S4), respectively. The AUROC curve of SWD for predicting fibrosis stage were 0.858(≥ S1), 0.886(≥ S2), 0.866(≥ S1) (≥ S3), 0.825(= S4). The AUROC curve of SWE for predicting inflammation activity were 0.846(≥ G1), 0.724(≥ G2), 0.787 (≥ G3), respectively. The AUROC curve of SWD for predicting inflammation activity were 0.777(≥ G1), 0.727(≥ G2), 0.803 (≥ G3), respectively. Conclusions For patients with liver tumors, ATI technology showed excellent feasibility and diagnostic performance for detecting and grading hepatic steatosis, SWE was more accurate in detecting fibrosis stage than SWD, SWD was not superior to SWE in detecting inflammation activity.

Background Atrial septal defect (ASD) can lead to volume overload and related changes in P‐wave parameters in surface electrocardiograms of these patients. In this study, we aimed to evaluate the effect of volume overload on P‐wave parameters in patients with ASD. Materials and Methods This study is a retrospective cohort analysis. A total of 142 patients with secundum ASD who underwent percutaneous closure were evaluated. P‐wave duration (Pmax) and P‐wave dispersion (PWD) were measured on the surface ECG before and 1 h after the closure procedure. We evaluated P‐wave parameters in terms of defect size, duration of the volume overload, and closure device sizes. Results Pmax and PWD were significantly decreased after the procedure compared with the values before the procedure (p < 0.001). Pmax values had a statistically significant correlation with ASD size (< 20 mm or ≥ 20 mm) both before and after the procedure. Pmax values were significantly higher in patients older than 30 years of age (119.6 ± 19.5 vs. 102.7 ± 17.1 ms, respectively; p = 0.039). A significantly positive correlation was found between pre‐ and post‐procedural Pmax and defect sizes (r = 0.474, p = 0.019 and r = 0.4233, p = 0.04, respectively). However, no positive correlation between PWD and defect age and size was present. Conclusion Percutaneous closure of ASD is associated with an immediate decrease in both Pd and Pmax that seems to be related to the acute volume overload cessation in cardiac chambers.

The so-called site effects caused by superficial geological layers may be responsible for strong ground motion amplification in certain configurations. We focus here on the industrialized Tricastin area, in the French Rhône valley, where a nuclear site is located. This area lies above an ancient Rhône Canyon whose lithology and geometry make it prone to site effects. This study presents preliminary measurements to investigate the local seismic amplification. We deployed three seismic stations in the area for several months: two stations were located above the canyon, the third one was located on a nearby reference rock site. The recorded seismicity was analysed using the Standard Spectral Ratio technique (SSR). The estimated amplification from weak motions reaches a value of 6 for some frequencies. These first results confirm the possibility of estimating seismic amplification using earthquakes recorded for less than one year, in this highly anthropogenic and industrialized environment, despite the local low-to-moderate level of seismicity. Noise-based SSR, that presents an obvious interest in such seismic context, shows also promising results in the area. To complement this empirical approach, we estimated the amplification using 1D wave propagation modelling. This numerical estimate is based on shear wave velocity profiles resulting from geophysical characterization campaigns. Comparison of the two approaches at low frequency, where numerical estimate is considered as the most representative, tends to suggest that edge-generated surface waves may have a strong influence in the local seismic response. This interpretation will be further investigated in the future.